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Gallery, Projects and General => Project Logs => Topic started by: Bogstandard on January 30, 2011, 06:01:21 PM

Title: Building the Minimag
Post by: Bogstandard on January 30, 2011, 06:01:21 PM
At last, I have started to be able to move on this little project.

For anyone who doesn't know what this is about, I suggest you have a look at this

http://madmodder.net/index.php?topic=4168.0

I received the kit about ten days ago, but building it has been held up by a couple of jobs in the shop and a few personal things.

I am not building yet, I am going to introduce you to the kit first.

I have got to say, this is a VERY complete kit, absolutely everything you need to make the unit except for a bit of superglue, a dab of loctite, and of course a bit of machining.
It is made up from a couple of different standards of fixings, all metric with just one bit of ME threads. But I suppose this is to take advantage of the cost of parts involved as it might be both cheaper and easier to source something like metric bearings and fasteners rather than imperial ones. The plans are also marked up in both standards, where needed. Things like that don't bother me at all, just take a bit more care as you do things, one good part at a time.
There is even a little bar of tufnol (or something similar), spring steel flat and a couple of tungsten rivet contacts supplied for making the points setup, as I said, everything is included.

The lighter in the shot gives some sort of scale.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD01.jpg)


I was at one time going to make one of these from scratch, from the book by the late Bob Shores, but the things that always put me off was winding the coil and making the punches for all the laminations (both coil and magneto). For a one off, a great deal of work.

No trouble on that score with this stuff. The coil is a work of art, fully potted, moulded to shape and sealed, not like a lot of model coils I have bought and used before, with their outer casings made from rolled cardboard, then all potted up with a soft wax like substance. This one really is the bees knees.

The strong magnet rotor is the same quality, fully potted and machined to size.

The laminations, are again, very well made, crisp cut, and on my kit, supplied as two sets, one left hand, one right hand.

The final main bits are the two roller bearings for the rotor shaft to run in.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD02.jpg)


The main part of the machining is making up the support block from the lump of ali supplied.
If care is taken, and the instructions followed, this should hold no terrors for anyone. It looks difficult, but if broken down into stages, it will emerge from the block like magic.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD03.jpg)


I will be following, as close as possible, the pre production build sequence and plans that Julian has provided me with. He has requested that I show no dimensions on this pre production build, just in case things change a little before it is released to the public. I fully agree with what he has asked me to do.

I will also be taking it a little deeper, giving a few hints and tips as I go along, so it should make healthy reading even for the novice, even if they are not needing one of these units.

I will be doing this in the same regime as I am building the flame licker. Most days, with a little luck, four hours work, if not, then two. I expect it to take around four to five days to complete, as I am a fairly slow but meticulous builder.

I do hope you follow along and enjoy it.


Bogs
Title: Re: Building the Minimag
Post by: ozzie46 on January 30, 2011, 06:41:47 PM
Got my seat picked out and patiently waiting.   :coffee: :coffee:

  Ron
Title: Re: Building the Minimag
Post by: Dean W on January 30, 2011, 06:59:26 PM
I think I'll watch!  I don't have a need for one (now), but they are kind of like a black magic box.  Everyone
wants to know the trick to the magic.  : )
John, I think he has an error line in the drawing you show.  The line that goes between the two uprights, on
top of the partially angled/partially bored piece that sticks out the front.  Maybe that line shouldn't be there.
That is, if the top surface it lies on is flat.  He may want to know, (or I'm mistaken).

Dean
Title: Re: Building the Minimag
Post by: madjackghengis on January 30, 2011, 08:37:08 PM
Hi John, glad to see the beginning of this  :whip: I was looking at what Bob Shores has put out as well, I believe I would like to be able to end up with one for the radial engine in the end, I think it can be done with a distributer attachment and some gearing.  I want to see how small this one you're building works out, and make a guess at whether I can use the basic principles.  I hope you can give some idea of relative size when it is all together. cheers, mad jack
Title: Re: Building the Minimag
Post by: jim on January 31, 2011, 01:32:25 AM
i'll be following this with interest.
Title: Re: Building the Minimag
Post by: NickG on January 31, 2011, 07:07:31 AM
I'll be watching too.  :thumbup:
Title: Re: Building the Minimag
Post by: Bogstandard on January 31, 2011, 08:05:45 PM
Now the basic kit intro is out of the way, could I please ask the members, unless it is directly related to this build, not to post things like, 'I built one thirty years ago' etc etc, could you please leave that to the very end, after the build is completed, and we can then discuss it.
If there is a question about techniques or procedures then please ask, but again, as this is a testing build for a commercial product, and I am following a set of build instructions, please, again, no 'I would have done it this way' type posts. But if you are relatively inexperienced, and don't understand what I have done, then please ask, I don't mind explaining the why's and wherefor's. Plus I don't want to put anyone off from commenting, that is what posts are all about, but please try to keep them fairly short.

I expect this post to be linked to, and maybe become a 'running commentary' to the paper build instructions supplied with the kit. Hence I don't need it to be a long drawn out post. Except for my bits. :)

For the more experienced amongst you, I will be going thru the build showing how I do a few basic machining techniques, purely for people with lesser experience, so please excuse me if I show what you already know.

BTW, if you can build an engine that one of these are required on, I see no problems at all in you building one of these.

 :ddb: :ddb: :ddb: :ddb: :ddb: :ddb: :ddb: :ddb: :ddb: :ddb:


So let's get on with it.


The very first thing is to assemble the supplied laminations. 32 pieces in each stack, one LH, one RH. After I put them together, I tightened up the screws and stuck a mic across them, just to make sure my count wasn't out, I came up with the same figure for both.
The nuts were then slackened off slightly, and a small bead of superglue run across the flat back side of the lams, in two places on each stack, between the screws. The glue wicked easily in between the parts, so things were quickly tightened up, wiped off the excess, and put them to one side. They will be used later in the build.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD04.jpg)


Whenever I come to do a new project on my machines, the first thing I do every time is get the machine ready to do a good job. If the machine isn't prepared, then expect crappy results.
The first job was to have a good clean up of the machine followed by a lube of all points. I am lucky in that I have one shot lube on my mill, but it is an important factor in getting precision. Oil forms a layer barrier between the metal working parts, it is that, if it is not there or 'topped up' can easily give you error of a couple of thou, so at the start of each working day, lube up.

The next part is getting you machine to cut straight, flat and square.
I go thru this routine religiously, even though not required.
With a DTI in my chuck, and a thick parallel in the vice, I sweep across the fixed jaw side from one side of the jaw to the other. If you don't have a parallel like this, and your vice fixed jaw face is in good condition, you could swipe along that.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD05.jpg)


It should read the same all the way across, if not, adjust the vice position until it is. Mine was still spot on, mainly because I have a bar on the bottom of my vice that locates into the table slot, and keeps it that way all the time. I just did this to show you what is required.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD06.jpg)


Next comes one of the most important bits, tramming the head. You might not think this is necessary, but without getting it spot on, what you think is a nice flycut flat surface just isn't, it will have a concave dippy down in the middle.

I made my own tramming tool, so it was laid on the table and the two gauges set to zero. You will have to find a way of doing your own tramming exercise if you haven't made one of these yet.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD07.jpg)


Tool now mounted into the spindle collet and brought down until at least one gauge reads zero. As you can see, my tram is out, not by far, but it needs putting right.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD08.jpg)


Swivelling the head a tiny amount soon had it spot on again.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD09.jpg)


Only last week, I was having a discussion with Stew about how a lot of people can achieve a nice flat face on the job, but just can't get it square to a face ajoining it. This is how I get faces square to each other when starting off with raw materials. I get everything square first, then bring them down to size.

Mark each end of the rough cut bar as shown. If bringing round to square, you machine the first flat and call it number 1, then carry on the same routine as this.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD10.jpg)


Put #1 side up, and if possible the bar sitting on parallels. No need to tap it down, just resting on them and tighten up the vice

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD11.jpg)


Then using you sharpest cutter, just clean up the face until all rounded corners are gone.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD12.jpg)


Before going any further with cutting, the bar is removed and deburred straight away and the vice given a good clean down.

The now cleaned up #1 face is now put against the fixed jaw and #2 face sitting at the top, and again only gently resting on paras. Between the moveable jaws and the job, you put in a piece of soft round bar to take up any irregularities. The bar in this shot could have been a little lower, say half way between the para top and the top of the jaw, that will give a more even pressure onto the #1 face against the fixed jaw.

The #2 face is then smoothed off, ensuring you end up with a nice sharp corner with #1 face.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD13.jpg)


After the cleanup and deburr, #1 goes against the fixed jaw, #2 goes down onto the paras and the soft bar is put into position and the vice tightened. Now you can tap the job down onto the paras. NOT belting it down, but a very gentle tap with a soft hammer. I use a lead hammer, but hold it by the head rather than the handle, that way I am not continually bouncing the job off the paras by hitting it too hard. If you are lucky, and have the first two faces square to each other, both paras should be gently trapped under the job.
This puts #3 at the top, and again that is flatted off.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD14.jpg)


For the last side, the soft bar is no longer needed. Because #'s 2 & 3 are parallel to each other and both square to #1, then #1 is tapped down onto the paras.
#4 is now skimmed down to give the correct dimension on the job.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD15.jpg)


If extreme care is taken, and at the end only tiny cuts, you can get rather close to perfect dimension, this is about 2/10ths of a thou out. Close enough for me.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD16.jpg)


Then it is just a matter of bringing the other pair down to dimension, in this case, spot on.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD17.jpg)


Now comes the little matter of getting the ends square to the other four faces. If you have an end mill that will cover the whole depth then you can just set the bar onto paras, with the end sticking out of the jaws and then just face it off.
In this case, I stood the bar on end with it overhanging the vice jaws. By shining a light onto the background, you can see how far out of square it is.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD18.jpg)


By gently tapping the correct way, you can get it sitting perfectly upright.
It looks like it isn't quite there at the bottom, but it is, what you are seeing is stray light shining on the corner of the block.
Make sure the vice is tightened up fairly well, but not enough to do damage to the part.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD19.jpg)


Then a very gentle skim over the top until all the rough sawcut marks are gone.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD20.jpg)


Nice and square.

All that is done now is the face just cut is sat down onto paras and the opposite end is brought down to final length.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD21.jpg)


Again, almost spot on.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD22.jpg)


This block took me nearly 1.5 hours to get cleaned up and down to size, but we are not in a production environment where time is money, so I don't worry about how much time it takes.

All I am interested in, is that when I come to machine this block up, because it is well finished, I won't have any troubles getting everything else to be in their correct positions.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD23.jpg)


So the next thing will be, hacking this lump down to about half it's weight.


Bogs
Title: Re: Building the Minimag
Post by: madjackghengis on February 01, 2011, 11:31:55 AM
Hi John, very nice and thorough entry into the project, hitting all the important parts for an accurate build.  A very good start.  :beer: cheers, mad jack
Title: Re: Building the Minimag
Post by: Bogstandard on February 01, 2011, 01:18:19 PM
Many thanks Jack,

I had an hour on it this morning, and because I had taken the time to get it as best I could, I had no troubles setting it up and getting some cutting done.

The way it has been designed, now I am getting into it, I reckon if you can get somewhere close, and get the other bits to fit, then the final truing up will put things right.

It doesn't need to be made as accurately as I have done, but as I am working to drawings with no tolerances shown, I am doing my best to keep to those sizes.


John
Title: Re: Building the Minimag
Post by: Bogstandard on February 01, 2011, 06:36:34 PM
A little bit more done today. It is time to start to cut bits out of the big ali lump.

Before I go into detail. Whenever I am cutting using a normal cutter, I very rarely attempt to do climb milling, sticking with conventional milling instead. My machine isn't geared up with the correct leadscrews to ensure it can be done safely, so I stay well clear of it normally.
There are plenty of descriptions about the difference between the two on the web, so if you are unsure about what I mean, then I would suggest you read and inwardly digest, to a point of where you think about it in your sleep. It could save your life one day.

On the build instructions, it says use the left hand top corner of the fixed jaw to set your basic 0,0 datum to. Unfortunately, I don't want to do that, purely because my vice doesn't support on the bottom of the job all the way to the outside of the jaw, on the KURT type, no problems on that score. So I will be moving my datum in towards the vice centre, and use my very rigid vice end stop as a substitute for the end of the jaw instead.

BTW, a few of the items I am showing have build posts for them on this site, vice back stop, tramming tool etc.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD24.jpg)


This is my setup, and it was an easy job with my edge finder to set up my datum corner.
I will just point out that the instructions do point to using a DRO for coordinate machining, but in my view, this magneto could easily be built plenty well enough by good layout and cutting to split the line.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD25.jpg)


In fact, even though I do have a DRO system, I still do a basic layout on a job such as this, purely as a double check as I am cutting.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD26.jpg)


Job mounted, pushed up to the backstop and gently tapped down onto paras, and the first cut on it's way.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD27.jpg)


On wide slots, or on any slot at all that needs to be accurate, I never use the correct width cutter to begin with. You will find that the cutter is usually flexed by the cutting forces involved, and will cut an oversized slot.

So in this case, a 16mm cutter run straight down the middle of where the slot is to be. It was taken down in stages until it was shy of full depth by 0.005". This is to allow a cleanup cut to be done at the very end.
Then I just gently crept sidewards to each marked line in turn.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD28.jpg)


As you get very close to the line, there are plenty of ways to measure to ensure you end up in the right place. On the finishing cut to the line, the tool was dropped to it's final depth and the cut was taken. The tool was then retracted up by 5 thou and the second line approached in the same manner.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD29.jpg)


Big slot in the right position, and to good size.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD30.jpg)


You then have to chew away at the two sides with the recommended 5/16" end mill. No problems in doing this, and it is at the same depth as the previous slot.
Except in my case, the marking fluid I used was washed away by the WD40 I use for cutting lube, and because my scribe lines were so feint, I overcut the length of the first slot by about 10 thou. But no problems, it isn't in a critical area and I just made the second one the same length, just to match it up.
None of us are perfect.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD31.jpg)


This is what you should end up with, minus ten thou on the rounded end.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD32.jpg)


The next bit is to lay a lamination against the slots just cut, and mark the 45 deg angled face onto the block. This is only a guide line, you fine tune as you cut it.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD33.jpg)


This bit had me perplexed for about thirty seconds.
The instructions suggest swivelling your vice by 45 degs either way to be able to machine to the lines. But as most people do, my swivelling base is languishing in the back of my shop somewhere, never to be seen again.

So I came up with this, a pair of V blocks, with both the blocks and the job being supported by the parallels. The cutter was already at the right depth, so it was just a matter of cutting the first one in the Y axis, and the second using the X axis.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD34.jpg)


Just like this, sneaking up on the angle so that the lam sits perfectly against all faces.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD35.jpg)


This is where the lamstacks will eventually be located. That is a job for next time.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD36.jpg)


A very boring day to follow. You will see.


Bogs
Title: Re: Building the Minimag
Post by: Ray on February 01, 2011, 08:07:00 PM
Bogs, this is a great build so far.  I appreciate you sharing your preparation with us. :thumbup:    Watching with a learning interest.  ironman (Ray)
Title: Re: Building the Minimag
Post by: Dean W on February 01, 2011, 09:35:06 PM
Good idea using the V-blocks, John.  Sometimes these solutions are sitting right in front of me, and I don't see it.
Again, good pics and descriptions.
Title: Re: Building the Minimag
Post by: raynerd on February 02, 2011, 04:01:49 AM
John, amazing first photos of squaring up the block. I learnt a hell of a lot!!

Chris
Title: Re: Building the Minimag
Post by: Bogstandard on February 02, 2011, 04:29:34 AM
Thanks you gents, and I am glad I am showing a few things that help people along their way.

I think I have found the right recipe of showing people how things are done. One or a couple of close up pics of the operation being done, plus a few words of text to explain it a little more. Well I hope I'm right, otherwise there will be a lot of confused people about the place.

I've just been having a think about the tooling that has been used so far, and I think most home shops have most of them. Three cutters, one pair of paras, a pair of V blocks and an assortment of cheapo Chinese micrometers, of which, after using them for a couple of years, I have come to trust as much as my very expensive counterparts, in fact in some situations, they are more accurate, as they have a vernier that reads to tenths. They could almost be classed as disposable precision tools for the amount I paid for them.

Just going out to the shop now, to see if I can get a little more done.


Bogs
Title: Re: Building the Minimag
Post by: NickG on February 02, 2011, 11:04:21 AM
Yeah thanks John, reading posts like this over the last few years are gradually teaching me how to do things properly in the workshop. I feel like I am either improving, or at least learning a new skill on every project I undertake now.

Nick
Title: Re: Building the Minimag
Post by: madjackghengis on February 02, 2011, 11:35:36 AM
Hi John, that was very nicely laid out, and well explained, beginning to end.  I really appreciated the innovative idea of the V-blocks, they were exactly what was needed, and far more accurate with no time lost, than trying to rotate the vise.  I'm keeping that idea for my next pass at a similar situation.  :beer: cheers, mad jack
Title: Re: Building the Minimag
Post by: Bogstandard on February 02, 2011, 05:47:19 PM
I'm doing well today, no unexpected visitors calling to stop me getting to my machinery.

Today is mainly about holes, both little and large. I just hope it doesn't end up being a boring post :D

As I have been tapping and tinkering around the mill vice for a few days, on start up, I double checked that my 0,0 datum hadn't moved. No worries, it was still exactly where I left it.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD37.jpg)


On the very detailed build instructions, it says that you can either spot thru the lamstacks to mark their mounting positions, or use co-ordinated drilling. It is difficult for me to hold and hit at the same time and still keep it accurate, so I have opted for the electronic DRO route. I did a bit of measuring of one of the lams and got my first datum point, then I could just use all the drawing dimensions. This is my working out.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD38.jpg)


Using my figures, I spot drilled all the points, plus one in the middle, I will tell you about that in a couple of minutes.
You might notice that I said spot drill rather than centre drill. Ever since these drills have dropped in price dramatically, I haven't used centre drills since, they are just too inaccurate and very prone to breakage. For those in the UK, this is where I get them from. About the cheapest you will find anywhere.

http://www.engineeringsupplies.co.uk/drilling-c-160.html?9=172&10=&11=192&12=&13=

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD39.jpg)


After spotting, I followed them up with a 2.5mm drill to a depth of 8mm, all except the odd one out.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD40.jpg)


Time for a bit of an assembly job.
You will find throughout this block machining exercise, you will add a bit more to allow you to machine a bit more.

So the holes were hand tapped out to 3mm and the bits were got ready to fit.
I would make a suggestion to do what I did, that is to clean down the lamstack holes, very gently, with a 3mm drill. Some of the glue had wicked it's way down to the hole area, and when I came to screw the screws back in, they were so tight, the lamstack started to split apart. So I stuck them up again, let 'em dry a bit, did the drill thingy and screwed them onto the block.

I had to add an extra lam to each side so that the brass lam sat flush with the surface. Spare lams are supplied for doing this very thing.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD41.jpg)


It looks like my drilling was OK.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD42.jpg)


At this stage the instructions suggest you mount the block into a 4 jaw on the lathe to do the boring. Unfortunately, that is very difficult for me to set up, and I find it much easier doing it on my mill. So you will have to imagine that what I am doing is on the lathe.

The spot drill point was refound by following the coordinates in the 'structions, and using a series of drills, I opened the hole up to the recommended 3/4". If you don't have drills of this sort of size, I would suggest you use the biggest you have, and bore the extra out.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD43.jpg)


Using my imperial boring head, the block was opened out to two distinct sizes, all very precise info is given in the build book, one all the way through, then the other to form a recess.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD44.jpg)


This is what it looks like.

The one all the way thru is to take the pair of bearings, and the recessed one for the rotor. You will notice that the boring operation has cleaned up the inside faces of the lamstacks.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD45.jpg)


So yet again, the block was put back to it's datum place.

This next stage takes you part way to fitting another bit, and also, why I wasn't worried when I overan the stack slot on the initial machining.

I am using a 5mm el cheapo Chinese end mill here, if it will do the job, why pay megabucks when you can get them for pennies.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD46.jpg)


Using the same technique as I used on the first large slot, a beginning slot was cut down to just shy of full depth, somewhere near the middle of where the slot needs to be.
I will be creeping towards the top area of the lams, and when I get there, put the cut to full depth and take a skimming cut across the top of the lams, just to clean them up.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD47.jpg)


Like this.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD48.jpg)


Now I needed to concentrate on getting the slot to a very snug fit around the lams in the coil. Measuring both sides up, they were the same size, but very slightly tapered back to front, larger at the front, perfect.

Get close, then using 1 thou cuts, gently open up the slot.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD49.jpg)


This is what I ended up with, the coil lams pushed fairly easily into the slot for the first 3/4 of the depth. When the holes are drilled and tapped, the screws will pull it in and form a perfect friction joint between coil and the two side lamstacks.

If they are too tight, a quickie swipe with a file will put it right, but that will be a bit later.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD50.jpg)

The coil bit has to be left now, while the cutouts in the block for the coil to fit into are done.

That is the next job.


Bogs
Title: Re: Building the Minimag
Post by: Dean W on February 02, 2011, 07:08:32 PM
Quite an interesting thread, John.  It takes shape fairly quick after a certain point.
Title: Re: Building the Minimag
Post by: ozzie46 on February 02, 2011, 07:49:46 PM


   Nice. Very well documented as usual John.

   Ron
Title: Re: Building the Minimag
Post by: Bogstandard on February 03, 2011, 01:26:15 AM
Thanks Dean & Ron.

On first post of this topic I showed a line drawing of the part I am now making, which to a novice looked rather daunting. But as I have progressed, it is showing that with a few basic machining techniques, the complicated looking part is starting to emerge, one bit at a time, and that is how you should view all overwhealming looking parts. Just a series of easy machining bits put together, to make the whole.


John
Title: Re: Building the Minimag
Post by: Bogstandard on February 03, 2011, 06:19:48 PM
And now the final part about hacking this block into shape. Great cheers from the audience  :nrocks: :nrocks:

This block seems to have taken an age to get to this stage, but what you must remember, I am now a very slow machinist and builder, so most reasonably experienced people could do this whole block easily in a full working day, if you have things organised.

This stage is now to get the block into the correct shape to accept the coil, which is sitting on top. If you look very closely, you can just see the layout lines for the required cutout.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD51.jpg)


The usual thing, straight down the middle with a big cutter, not quite to the bottom of the required slot, then go to each side in turn.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD52.jpg)


Just reaching the second side.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD53.jpg)


And this is what it turned out like.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD54.jpg)


This next bit is the final shaping of the block. The level bit is done first, then the angle.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD55.jpg)


Because the lamstacks were not quite flush or below the side faces, I used an extra set of paras, one either side, but not as far forwards as the lams, So allowing the block to be held rigidly. The horizontal cut was then taken to depth and the correct distance in.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD56.jpg)


Again, because I don't have a swivel base on my vice, I can't do the cuts as shown in the instructions.
Because this angle isn't super critical to the build, I continued to hold the block as before, with 4 paras, but eyeballed the angle and made sure that the bottom corner of the block was resting on both lower parallels.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD57.jpg)


Using a 10mm ball nosed cutter I cut up to the line by about 2/3rds down from the top. Then once the line was reached, I continued cutting straight down until it was almost at the horizontal face. Once it was taken out of the vice, I blended the radius in to the horizontal face with a round file and a bit of emery cloth.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD58.jpg)


That is all the cutting that is needed.
As can be seen from this side shot, the coil can now fit where it should.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD59.jpg)


And another shot from the front.

The holes in the coil were then spotted thru so that the holding screw holes can be drilled and tapped.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD60.jpg)


Even though the block is to shape, lots of holes need to be drilled. Their positions are all shown on the plans.

These holes thru the 'ears' are for a couple of grub screws, that if you haven't got quite a tight fit of the coil lams to the side lams, the coil lams can be forced down so good contact between the two is made.

Because I am a belt and braces person, even though I have good contact between them, I am going to use these as well.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD61.jpg)


The next job was to pick up the two spotted marks and drill the holding bolt holes to depth.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD62.jpg)


These four 2mm tapped holes are for a cover plate to fit over the rotor. This is optional, but I think it is a necessity, purely to stop bits sticking to the magnets in the rotor.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD63.jpg)


Then finally, the four magneto mounting screw holes.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD64.jpg)


All the holes were tapped to their correct sizes, and the coil checked for fit.
This block isn't quite finished with yet. It needs some bits making on the lathe and fitting, then the few remaing holes can be drilled. But other than that, this is that very complicated looking bit finished, just by carrying out some relatively simple machining exercises.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD65.jpg)


Onto the lathe next time.



Bogs
Title: Re: Building the Minimag
Post by: Ray on February 03, 2011, 08:45:07 PM
Bravo Bogs  :thumbup:  :clap:
Ray
Title: Re: Building the Minimag
Post by: madjackghengis on February 03, 2011, 10:52:46 PM
Hi John, very nicely done I must say.  I would take you for a former/present teacher from the way you lay this out.  You've provided some very needed info on the lams for a special project mag I have in mind.  Your set ups are very simple solutions to challenges which could easily leave some misalignment, and things not quite fitting exactly. :nrocks: very nice, mad jack
Title: Re: Building the Minimag
Post by: NickG on February 04, 2011, 04:56:11 AM
John, nicely done. This block was very similar to making the poppin frame - when I first looked at it I was thinking of different ways to do it as I couldn't imagine me making it. But when I started and followed mostly the sequence described, the block emerged (as you said) as if by magic and I can now see the virtues of doing it that way.

I used most of the techniques you have but when I make my next frame I will use this post to make sure I do exactly as you did and make a better component.

Thanks.

Nick
Title: Re: Building the Minimag
Post by: Bogstandard on February 04, 2011, 06:53:54 AM
Thanks gents, the comments are much appreciated.

One thing you must remember though, the way I do things are my way, just to make things easier for myself, like boring, I have great difficulty setting up my four jaw on the lathe, so prefer to use my mill.

Nothing is written in stone, and there are usually many ways to obtain the same end results.

As the less knowledgeable amongst you gain experience, you will find your own little ways and shortcuts to get to where you want to end up. Whether they end up the same way as I do it, you will have to wait and see.

I was on my lathe this morning, and for me it is a lot more stressful than using the mill, so I had to give up early, so it may not be much of a post later.


John
Title: Re: Building the Minimag
Post by: madjackghengis on February 04, 2011, 09:07:21 AM
Hi John, I truly understand the issues you have, with my own with the M.S., but you've done a good job figuring out what you can and can't do, and rearranging your work so you can accomplish what you want, in the time available, with what equipment you have, and I admire your commitment to continuing to work, and I fully understand that it is far more desireable than sitting out life in a closed room, waiting for life to close in on a person.  I wanted to say, the mag, as it sits now, very closely resembles a Fairbanks Morse or the like, except being open rather than all in a sealable machined box.  The way the laminations fit right in, and the means of machining around them, and through them has given me confidence I can at least have a decent chance at getting a mag to work with the radial engine, and I really don't much like the two options the project gives for ignition, one being points and the other a hall effect distributer, both with big coils, batteries, and the like.
    The way the machining cleared the way for the lams was very clean, and is the main source of my encouragement, as that was the issue I have been most concerned with, relative to getting a mag smaller than the engine, yet still with enough magnetic coupling to be an effective and responsive ignition system.  Are you going to have an engine to run a test sequence of the minimag on when it's finished? :beer: :ddb:  Just curious, mad jack
Title: Re: Building the Minimag
Post by: Bogstandard on February 04, 2011, 12:38:41 PM
Jack,

The engine hasn't been built yet, but I have already got a little design for a test stand, to check that everything works OK. I will also be doing a couple of cable strain relief parts as well, but they won't be just yet. I still need to get to the end of the build program, just to prove it.

Back into the shop again soon.

John
Title: Re: Building the Minimag
Post by: arnoldb on February 04, 2011, 02:02:13 PM
Thank you for posting in such detail John.  It is, as always, much appreciated.

Quote
As the less knowledgeable amongst you gain experience, you will find your own little ways and shortcuts to get to where you want to end up. Whether they end up the same way as I do it, you will have to wait and see.
There's a world of truth in that quote John - and I'll happily vouch for it as a novice with just a tiny bit of experience :-)

Kind regards, Arnold
Title: Re: Building the Minimag
Post by: sbwhart on February 04, 2011, 02:11:23 PM
Lovely Job John  :clap: :clap: :clap:

It came together very well, can't wait to see it on that engine.

Stew

Title: Re: Building the Minimag
Post by: Bogstandard on February 04, 2011, 05:25:31 PM
Just a little bit this time, but still progress.

I will just make a point about a couple of things.

The materials that have been supplied in the kit have been spot on for the job they have to do, and up to now they have machined beautifully, especially the aluminium, no tears, rips or picking up. It has been a joy to use.

The second concerns accuracy. For some of the parts made in the lathe, good accuracy IS required between certain ones, otherwise things will lock up or not, depending on what is required. This is especially critical on lengths of parts. So allow extra time just to make sure that things are really spot on.


I am now starting to do the lathe work, which concerns mainly the spindle, points operating cam and bearing fitment. The first piece called for is a spacer to go between the two spindle support bearings.


The instructions called for opening up the centre hole to a certain size with a drill and that is the job done.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD66.jpg)


Unfortunately, I can't be like that, so I opened it up to one size smaller and finished it off to shown size with a boring bar. It only takes a few minutes longer, and the surface finish is much better.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD67.jpg)


The outside size was turned down until it fitted into the thru hole with a nice sliding fit, not too tight as Loctite will be used, and that requires a bit of space to work in.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD68.jpg)


The spacer was parted off and brought to exact length.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD69.jpg)


The spacer needs to be fitted from the front face exactly the width of the bearing. So what I did, was to put the block face down with the bearing pushed all the way to the bottom of the thru hole and the back end of where the bearing sat was marked up with a felt tip.
The front bearing remains free to be taken out, so I had to ensure that no Loctite could get to it. By putting the drops of Loctite further in from this mark and assembling from this front side, the bearing will be safe.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD70.jpg)


The spacer was put in first, followed by the bearing, but not fully inserted. By pushing from the back of the mag block until the front hit the 321 block ensured that the bearing and spacer were in their correct positions, with the bearing flush with the front face. Another 321 was pushed up to the back face to keep things steady until the Loctite had done it's work, in this case, 5 minutes.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD71.jpg)


Next came the cam, very easy to make, but this is one component that does need to be made the correct length for it to adjust correctly.

The centre was first drilled then opened up with a 12mm reamer.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD72.jpg)


The outside was brought to size, then parted off and brought to length.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD73.jpg)


The cam blank was then tranferred to the mill using a square 5C collet block, and the flat face put onto the outside. There are lots of simple other ways that this could be done, so no worry on that score.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD74.jpg)


The block was then rotated 90 degs and the hole for the retaining grub screw drilled in the correct position.

It was then transferred back to the lathe to have the outside polished a bit and the flat blended a little into the side curves.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD75.jpg)


Once the grub screw hole was tapped out, the cam was finished. The instructions suggest that if you wanted to, you could case harden it. I will make that decision when I have made all the parts.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD76.jpg)


A bit more lathe work to follow.


Bogs




Title: Re: Building the Minimag
Post by: Dean W on February 04, 2011, 09:16:35 PM
It's all looking good, John.
I have to ask;  If you make more than one flat on the cam, will the mag be able to run more than one cylinder? 
I don't know about mags, so, just curious.  I'm sure someone else was dying to ask, so I'll play the silly one.  ; )
Title: Re: Building the Minimag
Post by: Bogstandard on February 04, 2011, 09:33:20 PM
Dean,

Instead of modifying the magneto, rather than driving it at half crankshaft speed (for a single 4 stroke), I suppose you could up the gearing to give you more beats to each crank revolution and use a distributor to feed the extra cylinders.


John
Title: Re: Building the Minimag
Post by: HS93 on February 04, 2011, 09:37:01 PM
could you not drill through from the outside and use a grub screw to hold the spaser with maybee a dimple to keep it in the correct place, not a fan of Locktite etc.

peter
Title: Re: Building the Minimag
Post by: Bogstandard on February 04, 2011, 09:45:46 PM
Peter,

Actually I am just following instructions, and if you had left your question to a little later, you will actually find that there are holes to be drilled thru the sleeve and main outer body and bits stuck down the holes that will in effect act like a grub screw to hold it in position.

The loctite, at this time, is only used to hold the spacer in the correct position until those holes are drilled.


John
Title: Re: Building the Minimag
Post by: Bogstandard on February 04, 2011, 09:48:24 PM
Gents, if you don't mind, at this time, could you please leave questions for another couple of days, until the build is completed, then we can then discuss it forever if needs be.

Many thanks


John
Title: Re: Building the Minimag
Post by: madjackghengis on February 05, 2011, 10:58:47 AM
Hi John, I'm really enjoying this mag build, I am a longtime use of magnetos, but the building of one of model size has not been something I've contemplated before, so this is affirming my notions of what is important, and how to do it most easily and get the best effect.  For those who wish information on magnetos in general, I am well versed with such of most types, and would gladly provide general magneto information, so as not to fill this log up with them.  All in all, I am quite pleased with how this build is going, and the quality of the components, the engineering which has been done, and of course, the excellent quality of the machinist who is doing the build.  I'm glad to see the great care exercized in getting everything right, and simple.   :beer: cheers, mad jack
Title: Re: Building the Minimag
Post by: Bogstandard on February 05, 2011, 02:30:38 PM
Thanks Jack.

Basically, todays offering is finishing off the main lathe work that is required. A few of the finishes look rough as old boots, but in fact they are very fine indeed. I think it is something to do with the lighting.

Carrying on from the last post, the spacer that sits inside the cam needs to made.

The first job was to drill and ream it out to 8mm.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD77.jpg)


The OD was then turned until the cam sleeve just fitted onto it with a nice sliding fit.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD78.jpg)


I actually deviated from the plans with this bit.

I lined up the cam sleeve with the end of the spacer and spotted thru the grub screw hole. This gave me a mark so that I could put in a small recess into the spacer.
The reason. When a grub screw is tightened, unless it has a soft end, it will throw up a burr. In this situation, where the cam sleeve has to rotate around the spacer, that burr will jam everything up and most probably cause problems when taking the whole shaft system apart. This groove will allow the burr to be below the running surfaces and so it won't cause a problem.

After this groove was done, the spacer was parted off and brought down to EXACTLY the same length as the larger bearing spacer made previously.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD79.jpg)


This is what it will look like when fitted inside the main block. The outer races of the bearings will be sitting against the larger spacer that is already stuck inside. So both the inner and outer races have the same length spacers between them.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD80.jpg)


This is it pulled apart.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD81.jpg)


The next job was to make up a 5/16" x 32 TPI ME thread half nut (sitting on top of the bearing) from the hex material supplied.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD82.jpg)


The final job of the day was to make the main 8mm diameter spindle from the ground stock that came in the kit.

First it was skimmed down to plan length, followed by tapping a 5mm thread into one end.

The other end was taken down to size for the projected sprocket or gear shaft and a matching thread for the nut put on, all to plan dimensions.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD83.jpg)


What the finished article looks like.

Actually there is nothing that was done today that should hold fears for anyone, except maybe having to single point threads if you don't have the correct taps and dies.

Also a little extra care is required to make sure you get dimensions spot on, rather than near enough.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD84.jpg)


To start to bring this build to a conclusion, the main block has to go back onto my mill and have a few holes drilled, the items shown in this picture made up into the contact breaker setup and be fitted into the block. Then just a dust cover for the rotor making, and it should then be ready for final assembly.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD85.jpg)


I will have to see how I feel tomorrow to see if it will get done this weekend.


Bogs
Title: Re: Building the Minimag
Post by: John Stevenson on February 05, 2011, 02:50:10 PM
John,
When you do these post you need to start two.

In this case one called "Building the Minimag"
and one called "Questions about building the Minimag"

This way if everyone behaves the main post is more of a blog with posts running sequentially and the other post stops the detractions.

In which case this post is in the wrong one  :doh:

John S.
Title: Re: Building the Minimag
Post by: Bogstandard on February 05, 2011, 03:51:40 PM
Many thanks for that idea John.

I doubt if ever I will get to build something like this again, with it's unique conditions, unless some other enterprising person wants me to try out their pre production build instructions, and of course, one of their kits.

As it is, I think the members have understood what the restrictions have been, and have really done their best to keep it fairly 'clean', I have no complaints at all.
On other sites, I reckon this post would be up to about 20 pages by now, despite the pleas, as I have done here.

They are a great bunch of chaps on here, with good willpower.

Hopefully in a couple of days, if they still want to, they can let the cat out of the bag.


John
Title: Re: Building the Minimag
Post by: Bogstandard on February 06, 2011, 06:02:32 PM
I am now into the finishing off stages.
Just a few holes to drill in the main block and make the points system. The holes are coordinate drilled from the dimensions shown on the plans and the points system is built up from the precise instructions as well, so I won't go into super detail unless someone asks about it.

Three holes are drilled in the top face, but I am showing this one especially.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD86.jpg)


The hole requires two operations, I went down first with a 2.5mm drill to give a recess in the bottom, it can be a fair amount deeper as it is only to give clearance, and then followed it down with a 6mm end mill to the specified depth. This forms the flat bottom hole that is required for correct fixing. See C-o-C below.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD87.jpg)


I hope this explains what I am on about. A very similar operation to fitting a bursting disc, or core plug as some people call them.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD94.jpg)


The fourth hole is drilled thru the side to allow access to the cam grub screw, to allow it to be adjusted.
Be very careful to drill the correct side. I nearly did the wrong one, but luckily caught it before making the mistake. It makes adjusting rather difficult if drilled in the other side.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD88.jpg)


At this stage, the screw for the main shaft was fitted and the rotor Loctited onto the shaft as far as it could go down.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD89.jpg)


A piece of supplied exact to size ferrule is cut to length and fitted into the centre hole. This hole is in fact reamed, and the ferrule should have been an interferance fit, but it wasn't, just a tight push. So uncle Loctite came to the rescue and fixed it.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD90.jpg)


At this stage three things had been completed. The first was to fit the ferrule in the centre hole flush with the top. The second was to tap the far hole out to 3mm. In fact, again belt and braces, I fitted a helicoil in there, to me it makes the tightening of the screw a lot more rigid. For the third bit, I had fitted the fixed point as shown in the above sketch.

You will also notice a brown stick thing poking up out of the ferrule. That is in fact a piece of Tufnol type rod, that when cut to the correct length will follow the cam and push up on the contact spring to make the points break, and so fire the stored energy in the coil.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD91.jpg)


The points system was then made up to instructions from a bit of spring steel strip with two holes drilled thru it (no problems with that, just good tapping lube and a slow speed), and a couple of insulators, plus of course a screw and solder tag.
I will just mention, in my supplied kit, if you are careful with the cutting, there was enough materials supplied to make up a replacement points part, just in case you buggered something up. But no spare tungsten points, so be careful with those.

The operating pin isn't finished just yet, as I still have a couple of jobs to do that requires the minimag to be stripped down. The first is the optional back cover, but the other is one of my own.
If you notice the upstands, I have carried on with the coil mounting screw holes and brought them out to the back.
I have a fetish about cables vibrating and swinging about, maybe fracturing. So I am going to use those two holes to hold some home made cable clamps, in keeping with the overall look.

So other than those, the Minimag is finished. It just needs to be timed to get the maximum spark out of it. That will be done later.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD92.jpg)


The back view, minus the cover plate.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD93.jpg)


So in the next few days, I will be making these extra bits, plus an operating stand to put it thru it's paces.

Overall I have really enjoyed making this little out of the ordinary piece of equipment. The materials supplied to me were excellent, the build instructions and plans have been modded in places, and that info has been passed onto Julian in the hope that he will take notice of them and modify accordingly.

So would I recommend this to a total beginner, no. But on the other hand, if you have made an engine for this to fit onto, then I see no problems at all. Just keep things as tight as you can.

Now open to questions and comments.


John
Title: Re: Building the Minimag
Post by: John Stevenson on February 06, 2011, 06:59:51 PM


Now open to questions and comments.


John

'Ave you had a belt off it yet ?  :lol:

John S.
Title: Re: Building the Minimag
Post by: Bogstandard on February 06, 2011, 07:04:28 PM
Not yet John, but I will have my brown trousers and wellies on when I come to set up the magnetic timing.


John
Title: Re: Building the Minimag
Post by: Divided he ad on February 06, 2011, 08:45:22 PM
Just read the whole post John... Well, read the first part, fell asleep (literature induced narcolepsy!) then woke up and just finished reading the rest   :palm:  :) Top build... looks bloody good  :thumbup:


Good luck with the setting up  :zap: 




It'll look great on the engine once it's built. Better than all the bulky electronic doodads and a chunky battery (IMHO).





Ralph.
Title: Re: Building the Minimag
Post by: madjackghengis on February 06, 2011, 10:35:35 PM
Well since the floor is open, I'll just say it out in my hardly every humble opinion, a nice maggie is always better than a lunking old battery and custom wirings with multi-colored splicings and terminals, on just about everything except maybe flamesuckers.  :lol:  Great build, and a great looking and set up magneto for an engine, far better, if it sparks reliably, than any battery based set up that is difficult to maintain between usages.  I see great potential for this magneto and look forward to using some of what I've learned here.  :bow: mad jack
Title: Re: Building the Minimag
Post by: Bogstandard on February 07, 2011, 01:44:09 AM
I have that effect on people Ralph, my continual gumbeating tends to send people to sleep. It is a shame it doesn't work on me, as I can't.


Jack, because of the bulkiness I would have to have (big box under the engine) was the main reason I went for it. If it all works, it will just sit on the camshaft end on the engine and will only require a fairly thin baseplate.


I noticed some pictures over on HMEM where a chappie had incorporated a couple of old Jim Shelley versions into their big upright aero engines.

Last two pictures on the first post

http://www.homemodelenginemachinist.com/index.php?topic=6432.0

Very neat installations.


John
Title: Re: Building the Minimag
Post by: sbwhart on February 07, 2011, 03:27:58 AM


Now open to questions and comments.


John

'Ave you had a belt off it yet ?  :lol:

John S.

It's a home made defibrillator to get you going in the morning  :zap:
 
:lol: :lol: :lol:

A great thread John really well shown.

Would it be posible if to encapsulate the little tungsten contact you belted in place with epoxy a sort of belt and epoxy fix or would that be going over the top and make it difficult to replace, if required.

Stew

Title: Re: Building the Minimag
Post by: Bogstandard on February 07, 2011, 03:46:24 AM
Actually Stew, it calls for a minute amount of Loctite to help hold it in position. Any more and it wouldnt be able to make electrical contact with the main frame, so I just gave it the persuassion treatment, and it is in there rock solid.
I honestly don't think anything else is required, but you never know once it gets up and running.

The points a very small BTW, even though I used self gripping tweezers, I still managed to drop one onto the floor, it was so close to being lost forever, as Mal hasn't cleaned up the floor since I hacked out the block and it is covered in ali swarf.

I am going to try to get in the shop this morning, in an attempt to finish the last few bits off, then after a couple of days rest, I should be able to get back onto the flamelicker build.


John
Title: Re: Building the Minimag
Post by: Divided he ad on February 07, 2011, 06:15:12 AM
It's not a slant on you John.... I fall asleep reading most of the posts on here!? I think it's a residual brian thing left from school?  :loco:



Those two aero engines look the business. a huge help in weight reduction for a plane if they ever get that far?

I'm not too sure about the croc' clip to connect to the spark plug? I'd be looking for something a little neater. Just my opinion.






Ralph.
Title: Re: Building the Minimag
Post by: Rob.Wilson on February 07, 2011, 11:44:15 AM
Hi John  :clap: :clap: :clap: :clap:


Cracking post as usual  :thumbup:  and a fine job you have made of machining it  :dremel:  ,,,,,,,,,,,,  were on the engine will you be fitting ?


Rob


Title: Re: Building the Minimag
Post by: ozzie46 on February 07, 2011, 11:51:46 AM



   As has been said before, well done John, well done.

   Ron
Title: Re: Building the Minimag
Post by: Bogstandard on February 07, 2011, 02:07:39 PM
Many thanks for all the good comments lads, I hope at least a couple of you have picked up a few tips.


Rob,

There a few way to fit it, and when the engine is built, the final decision will be made.

First off I could drive it from the main crank with say a 1/4" chain and sprocket, and reduce it down to half engine speed, that could be done from either side, and direction doesn't matter as it all depends on how it is magnetically timed, it can be driven either way.
But the favourite at this time is to take a 1 to 1 drive off the main engine valve cam, either directly mounted to, or what I am favouring at the moment, a drive gear or chain drive putting it to one side, and utilising the original points adjusting plate somehow, to allow me to easily adjust the ignition timing.

Basically putting it somewhere near where the original contact breaker points were to be. It all depends if I can squeeze it into the space.


John
Title: Re: Building the Minimag
Post by: John Stevenson on February 07, 2011, 02:14:23 PM
John, You need a gear drive like this to get it to give a right flick.

(http://www.stevenson-engineers.co.uk/files/eccentric%20gears.jpg)

Here's it in action  :D

http://www.youtube.com/watch?v=zOmSrePm_UM



John S.
Title: Re: Building the Minimag
Post by: Bogstandard on February 07, 2011, 02:23:59 PM
 :lol: :lol: :lol:

But I thought I could get away with a one tooth gear on each part  :bang:
Title: Re: Building the Minimag
Post by: Dean W on February 07, 2011, 09:22:21 PM
That gear setup would drive people loony, and they'd never notice the engine or mag it was running.  ; )

Bogs, it all turned out great!  It's a good looking little unit, and as always your work is very instructive.
Title: Re: Building the Minimag
Post by: madjackghengis on February 09, 2011, 12:09:09 PM
Well John, that is a very clean magneto, truly inspiring, and very neatly and solidly done.  I particularly like the points set up, out of the way, but easy to adjust, my question is regarding a condensor, is there one in circuit somewhere?  I have found a small magneto coil which looks about the same size or similar, on a weed eater engine, and I believe I can push the core, which is odd shaped, out, and push in a straight set of laminations, and try out building one using your demonstrated techniques on one which could fire nine cylinders, so I can use it on the radial build.  I looked at those two you put the link to, and they look to fit very well where they're at, and should be substantially better than batteries and such.  The aligator clip reminds me of the standard wire set up on all old cars, motorcycles and the like, with the end of the high tension lead having just a two pronged clip for connection to the plugs.  This has been a great build log, and if my mag experiment doesn't prove out, I will be ordering a minimag kit I expect.  Very nicely done, all around. :nrocks: :beer:cheers, mad jack
Title: Re: Building the Minimag
Post by: Bogstandard on February 09, 2011, 12:33:38 PM
I am just in the process of finishing it off Jack, but my body has told me otherwise, as usual.

No condensor required, just take the red lead to the plug and if the main body is earthed to the engine, you will have spark.

Stew took me out to the scrappies this morning, and one of the first things I picked up was some sort of garden machine engine, a tiny little thing, and that had a magneto sitting on the front of it. No bigger than the one I have made here.


John
Title: Re: Building the Minimag
Post by: cfellows on February 09, 2011, 02:52:33 PM
Very nice project, John.  Nicely documented.  Thank you for the time and effort to share.

Chuck
Title: Re: Building the Minimag
Post by: Stilldrillin on February 09, 2011, 03:22:27 PM
Nicely done..... Nicely shown, John.  :thumbup:

Yer said, don't say anything..... I didn't!   :wave:

Enjoyed the show. But, still got no meaningful comment.....  :scratch:

Thanks!

David D


Title: Re: Building the Minimag
Post by: Bogstandard on February 09, 2011, 03:31:22 PM
David, as long as you enjoyed reading it, that's all that matters and no comments needed. It is when no-one reads it is when the problems start.

Chuck,

I have sent you a PM.


John
Title: Re: Building the Minimag
Post by: John Stevenson on February 09, 2011, 04:15:11 PM


Stew took me out to the scrappies this morning, and one of the first things I picked up was some sort of garden machine engine, a tiny little thing, and that had a magneto sitting on the front of it. No bigger than the one I have made here.


John

Gloats are no good without pictures.
Title: Re: Building the Minimag
Post by: Bogstandard on February 09, 2011, 04:23:46 PM
No gloat John, I chucked it back in the skip as I've already got one now. :lol: :lol:

Now I can gloat


John
Title: Re: Building the Minimag
Post by: NickG on February 10, 2011, 05:29:03 AM
Haha, didn't realise you meant literally you just "picked it up" !

Was that the sort of thing I talked about in the other thread John? Chainsaw or strimmer type engine. I'm going to get one and do some experiments with that when I start my i.c. build.

Nick
Title: Re: Building the Minimag
Post by: Bogstandard on February 10, 2011, 06:41:12 AM
That's right Nick.

The magnets were actually embedded in the cooling fan on the front of the engine.

It looked a little complicated to get things how they would need to be, as rather than mechanical points, it had some sort of electromumbo gizzmo firing the spark, so I think I will stick with what I've got.


John
Title: Re: Building the Minimag
Post by: madjackghengis on February 10, 2011, 08:59:24 AM
Hi John, that thing you chucked back sounds like exactly what I have in hand myself.  I assume you've glanced at my build of the radial engine, and in truth, I've been off it for some time, waiting on parts, but in part, waiting for inspiration, as I don't want a big wooden box full of electrical mess as you described, and yet it must be reliable.  I've planned on attempting a magneto from the start, but until your build log, wasn't sure I was going to be satisfied in the end.  I still have to put together a rotor, and test my theory, but I think I can build a mag that is smaller than the engine, using ideas gained from your build, and if a mag can fit on it without interfering with any rotating parts, I'd be satisfied with it.  With my background in radar and electronics, I expect to make use of the built in trigger mechanism, and if I can't, I will end up using at the least, a coil from the minimag, as it is the right size, regardless of anything else.  A points or electronic ignition is easily built, but only a maggie is stand alone, and I feel an engine ought to be complete in and of its self, and hate to see electrics which are twice the size of the engine they run.  I appreciate the fact you've picked up a mag like I'm talking about, and have given me a comparative size review, as that supports my idea of getting one working for my purposes.  Your build was altogether a fine learning experience, and well done. :beer: cheers, mad jack
Title: Re: Building the Minimag
Post by: HS93 on February 10, 2011, 09:48:50 AM
Hi John, that thing you chucked back sounds like exactly what I have in hand myself.  I assume you've glanced at my build of the radial engine, and in truth, I've been off it for some time, waiting on parts, but in part, waiting for inspiration, as I don't want a big wooden box full of electrical mess as you described, and yet it must be reliable.  I've planned on attempting a magneto from the start, but until your build log, wasn't sure I was going to be satisfied in the end.  I still have to put together a rotor, and test my theory, but I think I can build a mag that is smaller than the engine, using ideas gained from your build, and if a mag can fit on it without interfering with any rotating parts, I'd be satisfied with it.  With my background in radar and electronics, I expect to make use of the built in trigger mechanism, and if I can't, I will end up using at the least, a coil from the minimag, as it is the right size, regardless of anything else.  A points or electronic ignition is easily built, but only a maggie is stand alone, and I feel an engine ought to be complete in and of its self, and hate to see electrics which are twice the size of the engine they run.  I appreciate the fact you've picked up a mag like I'm talking about, and have given me a comparative size review, as that supports my idea of getting one working for my purposes.  Your build was altogether a fine learning experience, and well done. :beer: cheers, mad jack

How about one of these, cheap simple and I think they do them for more cylinders as well.
peter
http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=10996

http://www.hobbyking.com/hobbyking/store/uh_viewItem.asp?idProduct=9906
Title: Re: Building the Minimag
Post by: NickG on February 10, 2011, 09:57:48 AM
Yeah you're right John, I don't think it'd be a simple task to modify it. It'd have to be hidden away under a box I think too, don't think it'd look pretty.

Peter, the point of this is, it is self sufficient i.e. doesn't need anything else to make it run other than fuel and authentic!
Title: Re: Building the Minimag
Post by: HS93 on February 10, 2011, 10:02:33 AM
It was realy just to see if it would help madjackghengis from the post above mine. I prefer the mag as well for older engines, but some members also build more modern engines as well.

Peter
Title: Re: Building the Minimag
Post by: kvom on February 10, 2011, 11:17:10 AM
As someone who failed his electricity classes, can someone confirm my understanding of this?

The shaft of the minimag is connected to the shaft(?) of the IC engine and acts as a generator to provide energy to the engine's spark plugs.

I haven't attempted an IC engine yet, and won't likely do so for a while, but I enjoyed following along with the build.
Title: Re: Building the Minimag
Post by: Bogstandard on February 10, 2011, 01:07:11 PM
Kvom,

You are quite correct.

The shaft thru the Minimag should be driven at half engine speed for a 4 stroke, either thru gears or chain from the engine crank or direct from the camshaft, which runs at half engine speed. But having said that, you could run it at crankshaft speed and use the 'wasted spark' method of ignition. For a two stroke engine, you run it direct from the crankshaft.

As the magnetic rotor turns inside the soft iron laminations, it produces energy which is stored in the coil. As the mechanical points on the magneto open, the charge inside the coil is released to the positive lead (red), which, if connected to a spark plug with the outside of it earthed to the magneto, a spark will be fired across the gap in the plug.

But if you hold onto the bare wired red lead with your fingers, and turn the rotor with your other hand, you end up with a curly haircut and brown trousers, as up to 10,000 volts is produced, and your body reacts to this high voltage with the previously mentioned symptoms.

Basically, it is a stand alone unit, driven by the engine, and produces it's own power to fire the spark plug, with nothing else required at all. Turn the engine, spark plug fires, engine continues running until it runs out of fuel, or the line to the spark plug is broken.

John

Title: Re: Building the Minimag
Post by: madjackghengis on February 11, 2011, 10:06:49 AM
John, Nick, Kvom, Peter and all, I've built Harleys for a living my whole life, as a side job most of it, with two decades in the Marines on active duty, and the single factor which most often causes breakdowns is batteries and electrical problems.  I've run magnetos on every bike I've had, as well as every kind of ignition available, and having the ignition in its own, dedicated package, is as close to getting a gas engine self-sufficient as a diesel is, as is practicable.  I can very easily make the points distributor or the electronic ignition distributor with hall effect parts, that are both in the engine's plans, but as John says, that leaves a battery in a box, and electronics in the box, and I want the reliability and stand alone capacity of a weedeater.  While a magneto on a full sized radial engine is perhaps shoe box sized for each of two, on an engine six or seven feet in diameter, and I'll be lucky if I can get the mag under half the size of the engine its self, simply being self standing is important to me, because it more closely matches reality.  In truth, I could use glow plugs and just eliminate the sparks, but then it would not be a timed, well running engine.  The engine which I use for my icon, is a 103 cu in Harley engine, with both an electronic distributor, and a centrifugally advanced magneto, and it has dual plugs, one set fired by electronics, the other pair fired by the distributor.  The electronics is a high tech bought piece of equipment, while the magneto set up is custom built into the engine, designed and built by myself, to match the specs of the electronics for timing and advance.  I don't know at this point, if I will be successful in my endeavor to build a nine cylinder magneto, but John's build has given me high hopes for the first time since I started the radial engine three or so years ago.  I have perhaps fifteen or twenty different kinds of magnetos on my shelves, dating from turn of the last century to brand new on engines, all working, and except for the very new ones, all doing it exactly the same way, with the new ones using a hall effect pickup built in to eliminate the points.  John's build shows me it's possible, so I will pursue it until it fires my engine, or I give up in failure, and put a distributor on the engine.  The magneto was among the greatest advances in i/c engine design, to this day, IMNHO, and it remains almost unchanged and equally effective more than a hundred years after it made its debut.  I like them, they fit my ideals:  "KISS, or keep it simple, stupid" and it looks possible.  What more could a model engineer ask for? :nrocks: :headbang: :beer: cheers, mad jack
Title: Re: Building the Minimag
Post by: Bogstandard on February 13, 2011, 07:18:41 AM
Sorry this final post has taken so long, I had done a little bit too much , so I just took a nice steady rest.


The plate that covers the rotor was made to drawings, and as you can see, it had to have a big hole in it to give the rotor somewhere to stick out into.  I still thought it wasn't really swarf proof, so I turned up a disc with a very shallow spigot on it to fit into the hole and duly soft soldered it in.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD95.jpg)


Unfortunately, I had to a bit of bling as well. So my trademark of concentric circles and a bit of playing about with my latest digital toy, my rotary table, I came up with this.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD96.jpg)


The cable strain reliefs were made and fitted, just to stop the cable from flopping about all over the place due to vibration, and maybe later on causing a breakdown due to fracturing of the inner strands.

The test rig was then made up and the Minimag given a turning over. I tried to get a vid of it showing the sparks on the plug, but underneath the lights you couldn't see them hardly at all, and in the pitch black my camera wouldn't work, so my word will have to do.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD97.jpg)


So the unit has been built and tested, I will just have to wait until my big engine is built to see if it works OK on that.

I'm sorry I can't go into more detail, but this post has over run by over a week, so I must now get back to the flamelicker project, otherwise that will end up in a box somewhere.

I hope you have enjoyed the journey.


Bogs

Title: Re: Building the Minimag
Post by: John Stevenson on February 13, 2011, 08:28:36 AM
Grab hold of the plug lead, give it a whirl and get Mo to get a video of you dancing about.

Unless you do this we won't believe you  :poke:

John S.
Title: Re: Building the Minimag
Post by: NickG on February 13, 2011, 10:35:34 AM
 :lol:  You should have put a disclaimer on there John S in case bogs tries it and it all goes wrong!  :palm:
Title: Re: Building the Minimag
Post by: HS93 on February 13, 2011, 11:02:37 AM
Tie a chew stick to the handle and bandit will turn it for you, that way you can hold the plug and camera :lol: :lol:

 :worthless:

    :ddb: :ddb: peter  :ddb: :ddb:
Title: Re: Building the Minimag
Post by: madjackghengis on February 13, 2011, 11:35:27 AM
Great close to a fine build log, your bit of "bling" looks good, and I'm willing to take your word on the spark, at the same time, I will echo John S.'s comments, and Nick's as well.  Is it possible for you to extrapolate some on how you found the "sweet spot" to set the points break at, and comment on the apparent lack of a condensor?  I have long assumed the condensor for these modern maggies with electronic control, are embedded in that part of the magneto, but that has been an assumption, because I didn't want to tear apart a working magneto and find out.  All the other magnetos I've worked on have had a condensor, and a bad one will definitely disable a working magneto.  I would also say your test rig for the magneto is very good and something I will have to emulate, not having at least three hands myself.  Thanks much for this very clear presentation.  :nrocks: :beer: cheers, mad jack
Title: Re: Building the Minimag
Post by: Bogstandard on February 13, 2011, 12:29:08 PM
I just knew you lot would have me dancing about with curly hair (what I have left of it) and the a**e of my pants on fire.

Just to answer Jack's question.

The 'sweet spot', depending on your required direction of rotation is just as the rotor 'goes over the top', you can feel it being forced away forwards. The spot is that the points should just be starting to open somewhere between then and about ten degrees after, you need to tweak to find the point of best spark. It took me no more than 10 minutes playing about to find the optimum position.

During my dark session, I was driving it with a portable drill, and noticed that the contact points did flash occasionally, about once every five or six seconds, suggesting that a condensor might be needed to suppress that, but I can attest that none is required for normal running, there were plenty of sparks flying about on the plug tip with a 0.040" (1mm) gap on the plug and 0.010" (0.25mm) gap on the points.

I hope that answers most of your questions.

I hope to start back on the flame licker tomorrow.


John
Title: Re: Building the Minimag
Post by: madjackghengis on February 13, 2011, 01:37:56 PM
Hi John, thanks much for clarifying all of that, glad to hear it sparks across forty thousandths, that should fire well under compression.  I'm looking forward to your flame sucker getting back on schedule.  This has been a very enlightening build log, thanks much.  :nrocks: jack
Title: Re: Building the Minimag
Post by: Dean W on February 13, 2011, 04:02:25 PM
Was an informative build thread, John.  The finished item looks the part, too.  Very nice.
Thanks!
Title: Re: Building the Minimag
Post by: John Stevenson on February 13, 2011, 05:21:51 PM
I like the nice touch of the strain relief.

John S.
Title: Re: Building the Minimag
Post by: krv3000 on February 13, 2011, 06:27:41 PM
WELL dun brill work  :) :)
Title: Re: Building the Minimag
Post by: lordedmond on February 14, 2011, 03:38:17 AM
Sorry this final post has taken so long, I had done a little bit too much , so I just took a nice steady rest.


The plate that covers the rotor was made to drawings, and as you can see, it had to have a big hole in it to give the rotor somewhere to stick out into.  I still thought it wasn't really swarf proof, so I turned up a disc with a very shallow spigot on it to fit into the hole and duly soft soldered it in.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD95.jpg)


Unfortunately, I had to a bit of bling as well. So my trademark of concentric circles and a bit of playing about with my latest digital toy, my rotary table, I came up with this.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD96.jpg)


The cable strain reliefs were made and fitted, just to stop the cable from flopping about all over the place due to vibration, and maybe later on causing a breakdown due to fracturing of the inner strands.

The test rig was then made up and the Minimag given a turning over. I tried to get a vid of it showing the sparks on the plug, but underneath the lights you couldn't see them hardly at all, and in the pitch black my camera wouldn't work, so my word will have to do.

(http://i202.photobucket.com/albums/aa102/bogstandard_photos/From%20June2010/MAGBUILD97.jpg)


So the unit has been built and tested, I will just have to wait until my big engine is built to see if it works OK on that.

I'm sorry I can't go into more detail, but this post has over run by over a week, so I must now get back to the flamelicker project, otherwise that will end up in a box somewhere.

I hope you have enjoyed the journey.


Bogs




John
As you comment on a low output have you tried it without the new cover ?

as I am an Electrical Eng ( when I when to work 14 years ago ) consider that the brass cover plate could be presenting  a single shorted turn to the magnet

maybe try without the cover , if this works then make the cover out of a none conductor

Stuart
Title: Re: Building the Minimag
Post by: Bogstandard on February 14, 2011, 04:49:33 AM
Stuart,

I never commented about low output, just that under bright lights the camera couldn't pick up the spark too well. In darkness there was enough sparks for everyone and his dog.

The back plate is in fact part of the original build sequence, and there is no difference to the sparks whether it is there or not.


John
Title: Re: Building the Minimag
Post by: lordedmond on February 14, 2011, 05:08:12 AM
John

Sorry I misunderstood your comment

It was just a comment as I have come across similar problems in the past with brass plates and magnetic devices


In one case some cables had been installed with brass bushes round each core , result brass got so hot it melted the insulation on the cables


Stuart
Title: Re: Building the Minimag
Post by: Bogstandard on February 21, 2011, 06:20:00 PM
I have a few apoligies to do on this post.

All those that queried why this unit didn't have a condensor and I replied that none was supplied and as far as I knew it didn't require one.

Anyhow, talking thru things with Julian, he did mention that even though there is no external condensor with the Minimag, the coil actually has one built into it and is all contained within the potting shell.

Anyway that bit is now explained, and for all you doubting Thomases, and especially of interest to the Webster builders.

Because I don't have an engine to try my Minimag out on, Julian very kindly cobbled together a mounting and has done a video of his Webster running with my Minimag doing it's own thing.

http://www.youtube.com/watch?v=XiJphgWRZLg

The extra 'clicking' towards the end is radio interferance.

Bogs
Title: Re: Building the Minimag
Post by: sbwhart on February 22, 2011, 02:55:57 AM
Love that crazey beat  :headbang: :headbang: :headbang: :headbang: :headbang:

Very nice

Stew
Title: Re: Building the Minimag
Post by: Stilldrillin on February 22, 2011, 03:34:29 AM
Poetry!  :thumbup:

David D
Title: Re: Building the Minimag
Post by: NickG on February 22, 2011, 04:10:23 PM
Brilliant!  :thumbup:
Title: Re: Building the Minimag
Post by: Bogstandard on May 03, 2011, 03:38:23 PM
I thought that this post was done and dusted, but it seems not quite.

Julian, the supplier called me today, just for a general chat to tell me that sales of the Minimag are now climbing, and that he is returning my unit, and with it, he will be sending a new neo magnet that he is going to be trying out, to see if it will give even bigger sparks at much lower revs. I will give an update when I can get around to it.

We also discussed a little about the chain drive, and he stated that he is using an 8mm wide one, plus also, because of the slight slackness in the chain drive, it somehow gives a spark boost as it comes up to the generation stage, the chain sort of lags a little as the pressure from the magnet is felt, then gives a forwards kick when the chain takes up the slack. A very interesting phenomenon, and I suppose could also be realised with a geared drive, if the mesh was left a little on the slack side.

I have already decided I will be going with a smaller chain drive system, these people do a 6mm wide series for very reasonable prices.

http://www.technobotsonline.com/index.php?dispatch=categories.view&category_id=193


Bogs
Title: Re: Building the Minimag
Post by: John Stevenson on May 03, 2011, 03:46:15 PM
Sounds a bit like the impulse magneto's where the drive pauses, winds a spring up and then lets go.

John S.
Title: Re: Building the Minimag
Post by: madjackghengis on May 04, 2011, 11:40:07 AM
Hi John, I just had to go through this build log again, what with a new posting, and was reminded of the rare earth magnets you were going to be putting in to test for low speed operation, I'm hoping you will be posting a similar video of the outcome of that, the Webster with your maggie is a very impressive display, in a large part because it is merely idling, which where mags are weakest, and show their faults, and yours runs perfectly at that speed.  I'm looking forward to what comes out of the neo magnet replacement, and hope to see some testing.  I've got a spark tester for cars, essentially a point with a clamp on it, with a plastic holder holding a screw with a point, and a clear cover, so you can adjust the distance the spark has to jump, and it's a good "seat of the pants" test of how much energy the spark actually carries, better than just a "fat" spark at the plug, or a "weak and skinny" one.  Just cleaning a working magneto, getting the brass contacts for the high voltage clean, and ensuring clean points and good gap can easily double the spark output and it is a repeatable test with this little cheap and easy bit of tool.  In any case, it was good to refresh my mind on your magggie build and the success you show is available for such engines. :beer:  Cheers, Jack
Title: Re: Building the Minimag
Post by: Bogstandard on May 04, 2011, 12:29:49 PM
You might be quite correct on that John, but if it does allow a larger or stronger spark to be produced, then advantage has to be taken of it. So a bit of a slack drive it is.


Jack,

I received my unit back today, and as promised, he has sent me a specially made sintered neo magnet, that looks to be either chrome or nickel plated to make it a little stronger, as they are renowned for being a little susceptible to shock loads. But because of the the size it has been made to means that a slight mod to the main frame and a couple of new parts will need to be made before it can be tested again, so that might take a bit of time before I can get around to it.


John
Title: Re: Building the Minimag
Post by: narrowgauger on May 04, 2011, 08:29:26 PM
Hi Bogs

noted that you were using some small roller chain.  Looking at the dimensions of the chain you are using it seems to me that this is still rather oversized and out of scale with the model.

as an alternative roller chain may I suggest the following miniature stainless steel chain from Precision Scale Model Engineering ( psme@psmescale.com ):

Title: Re: Building the Minimag
Post by: Bogstandard on May 05, 2011, 12:27:01 AM
Bernard,

Many thanks for taking the trouble to reply and attempting to assist me.

But in reality, 6mm chain and sprockets will be perfect for the job to come. The engine it will be fitted onto actually has two rather large 9" flywheels, unlike the very small engine that was shown in the video.

Thanks again


Bogs