Building the Minimag

[madjackghengis]

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?   Just curious, mad jack

[Bogstandard]

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

[arnoldb]

Thank you for posting in such detail John.  It is, as always, much appreciated.

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

[sbwhart]

Lovely Job John 

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

Stew

[Bogstandard]

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.




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.




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.




The spacer was parted off and brought to exact length.




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.




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.




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.




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




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.




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.




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.




A bit more lathe work to follow.


Bogs

[Dean W]

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.  ; )

[Bogstandard]

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

[HS93]

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

[Bogstandard]

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

[Bogstandard]

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

[madjackghengis]

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.    cheers, mad jack

[Bogstandard]

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.




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




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.




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.




This is it pulled apart.




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.




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.




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.




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.




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


Bogs

[John Stevenson]

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 

John S.

[Bogstandard]

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

[Bogstandard]

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.




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.




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.




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.




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.




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.




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.




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.




The back view, minus the cover plate.




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

[John Stevenson]

Now open to questions and comments.


John

'Ave you had a belt off it yet ? 

John S.

[Bogstandard]

Not yet John, but I will have my brown trousers and wellies on when I come to set up the magnetic timing.


John

[Divided he ad]

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     Top build... looks bloody good 


Good luck with the setting up   




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





Ralph.

[madjackghengis]

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.    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.  mad jack

[Bogstandard]

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

[sbwhart]

Now open to questions and comments.


John

'Ave you had a belt off it yet ? 

John S.

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


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

[Bogstandard]

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

[Divided he ad]

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? 



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.

[Rob.Wilson]

Hi John 


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


Rob

[ozzie46]

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

   Ron