Author Topic: Minnie on the cheap!  (Read 2087 times)

Offline NormanV

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Minnie on the cheap!
« on: August 17, 2017, 01:31:13 PM »
A few months ago I went to an Autojumble and found a model boiler for sale for £5! I snapped it up and took it home with glee. After some investigation I found that it was the boiler for the Minnie traction engine, but, a big but, it was made in steel. I thought about it and realised that if I made this engine I would probably only steam it once or twice and mostly run it on compressed air. So a steel boiler would be fine.
I am short on cash so have to make it as cheaply as possible. The commercially available castings are quite expensive for a pauper!
For example, the aluminium castings for the rear wheel rims are £70, I made them for the cost of the gas for my furnace. These will appear later.
My current problem is the castings for the bearings, the commercially available ones are bronze. What type of bronze? Can I cast them myself? It would be nice to make accurate castings. I have made the patterns in aluminium and have made the moulds in plaster of paris.
Bronze, there is bronze that is an alloy of copper and tin or an alloy of copper and aluminium. Lead free solder (99c) is almost pure tin, I could use that. There are so many variables. Whatever I use will not be perfect but will probably be good enough for what I want to do. Will my mild steel crucible be enough for the job? Time will tell.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #1 on: August 17, 2017, 01:34:37 PM »
Here are my moulds for the bearings.
The second picture is the moulds in the oven to dry them out.
I don't have a wife to answer to!

Offline NormanV

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Re: Minnie on the cheap!
« Reply #2 on: August 17, 2017, 01:36:55 PM »
The location bumps were cut freehand with a ballend mill.

Offline awemawson

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Re: Minnie on the cheap!
« Reply #3 on: August 17, 2017, 02:20:50 PM »
Babbitt bearings have a good lineage in that they take large loads and are relatively simple to cast around the shaft that needs support.

https://en.wikipedia.org/wiki/Babbitt_(alloy)
Andrew Mawson
East Sussex

Offline Pete W.

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Re: Minnie on the cheap!
« Reply #4 on: August 17, 2017, 04:08:24 PM »
Hi there, Norman,

The Copper Development Association published a comprehensive book entitled 'Aluminium Bronze'.  I understand that all their publications, including that one, are now available on-line.

One bit I remember from the chapter about casting Aluminium Bronze is that if there are multiple paths around the mould cavity, e.g. around the core or a branched feeder, the two streams of molten metal won't merge properly when they meet.  I guess it's because the stream of molten metal has an oxide skin.  I also seem to remember a comparison with pouring beer into a glass!

Apart from that, aluminium bronze works well immersed in water and is fairly easy to machine.  All that from memory, I suggest that you seek the .pdf. 
Best regards,

Pete W.

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Offline NormanV

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Re: Minnie on the cheap!
« Reply #5 on: August 17, 2017, 06:12:14 PM »
The way I was proposing to cast it would not involve two streams of metal meeting. I will let you know how it works when I can find the copper.

Offline Jasonb

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Re: Minnie on the cheap!
« Reply #6 on: August 18, 2017, 03:00:20 AM »
I'd just cast the bearings in aluminium and then bore them out slightly oversize and sleeve then with an offcut of bronze or brass.

I had a bad casting on one of mine and just cut the flange from a bit of 1/8" steel and soldered on the teardrop shaped part.

Another alternative as you can obviously machine them from solid is to do then in cast iron cut from an old square sash weight, shafts will run OK in the iron.

If you do want to cast in bronze then old stop cock and gate valve bodies are often DZR bronze and would do the job as the bearings won't be seeing much use if you are just going to run on air.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #7 on: August 18, 2017, 05:20:37 AM »
I have cast the wheel hubs in aluminium and sleeved them but I just wanted an excuse to try casting bronze. It is also quite interesting to try using a plaster mould taken from machined metal patterns that are more accurate than what I could produce using wood.

Offline Pete W.

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Re: Minnie on the cheap!
« Reply #8 on: August 18, 2017, 08:40:22 AM »
I think you'll have fewer problems with the copper + tin variety than with aluminium bronze. 
Best regards,

Pete W.

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Offline NormanV

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Re: Minnie on the cheap!
« Reply #9 on: August 19, 2017, 03:38:18 PM »
Pete, what sort of problems am I likely to have? I would have to buy the tin, I've got aluminium.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #10 on: August 19, 2017, 03:45:01 PM »
Some more parts, the wheel rims. I can't understand why the castings for the rear rims are so expensive (£70)! They cost me next to nothing to cast them myself.
The strakes on the hind wheels were a bit tedious to make but riveting them was fun.
Also the wheel hubs and associated bits. The slots for the spokes are a bit rough, I made my own milling cutter, it didn't keep its edge, but it won't matter as the hub covers will hide it all.

Offline krv3000

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Re: Minnie on the cheap!
« Reply #11 on: August 19, 2017, 04:36:40 PM »
hi brill work nothing rong with things dun with watt you have at hand 

Offline Pete W.

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Re: Minnie on the cheap!
« Reply #12 on: August 19, 2017, 05:30:28 PM »
Pete, what sort of problems am I likely to have? I would have to buy the tin, I've got aluminium.
 

Have a look here:  https://www.copper.org/resources/properties/microstructure/al_bronzes.html 

Oops, sorry, that's the wrong publication.  Still, if you Google 'Copper Development Association', there are several publications on Aluminium Bronze.  It's a bit near bed-time right now - I'll have a look for my hard copy tomorrow and post here again with the CDA publication number. 
Best regards,

Pete W.

If you can keep your head when all about you are losing theirs, you haven't seen the latest change-note!

Offline NormanV

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Re: Minnie on the cheap!
« Reply #13 on: September 11, 2017, 02:20:59 PM »
I gave up on the idea of making bronze castings for the bearings as I could not source any copper. Instead I thought that I would cast them in aluminium and sleeve them in a more hard wearing metal. The castings in my expensive plaster moulds were a failure. I believe that as the plaster was cold it caused the metal to shrink away from them. My precise sharp cornered patterns were translated into rounded cornered castings!
What a waste of money, £12 for the plaster.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #14 on: September 11, 2017, 02:24:28 PM »
So instead, I fabricated to bearings in steel. I do not have any silver solder so I araldited the parts together. They look ok, remember, this is intended to be a display model rather than a fully functioning one.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #15 on: September 11, 2017, 02:31:55 PM »
The plan calls for ground steel for the shafts, I decided to turn them from oversize metals. The longest shaft is 12mm dia x 200mm long. I turned it between centres and initially it turned out oversize at the tailstock end but a bash with a hammer on the tailstock ended up with it being parallel over the whole length. I am quite pleased with that. After that the other shafts, only 100mm long, were a doddle.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #16 on: September 11, 2017, 02:34:33 PM »
The crankshaft was my next attempt. I made it in three pieces and loctited it together. I will pin it when I have the material for the pins.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #17 on: September 20, 2017, 01:05:26 PM »
Making the spokes was tedious. I tried a couple of different approaches but it just needed patience and I got there in the end.
I started on the front wheels as they seemed easier.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #18 on: September 20, 2017, 01:07:11 PM »
And here are both front wheels completed and mounted on the axle.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #19 on: September 20, 2017, 01:08:42 PM »
Today I started on the rear wheels.
Wheel building is fun, and progress is quite rapid.
« Last Edit: September 20, 2017, 02:39:13 PM by NormanV »

Offline NormanV

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Re: Minnie on the cheap!
« Reply #20 on: October 03, 2017, 02:53:53 PM »
I notice that I am not getting much response to this thread, I suppose it is because there are many Minnies that have been built and nobody is interested any more.
I have a question. I want to cut the gears myself, I have never done it before. It appears that there are two approaches, I could hob the gears which seems to only need one cutter or I could use a set of cutters to cut individual teeth. A ready made hob costs approximately £45 the material to make it costs £25. It hardly seems worth the risk of cocking it up so I would prefer to buy a ready made one. The individual cutters are £25 each, I would need 4 totalling £100. Buying ready made gears is starting to sound attractive!
Here is my question, would my milling machine with its 1/2 Horsepower motor have sufficient power to use a hob?

Offline eskoilola

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Re: Minnie on the cheap!
« Reply #21 on: October 03, 2017, 03:31:57 PM »
Actually.

You might consider making the gear cutter Yourself. It is not that hard after all.

The process described in the link below seems to be quite understandable even for me  :coffee:

http://www.helicron.net/workshop/gearcutting/gear_cutter/

Offline tom osselton

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Re: Minnie on the cheap!
« Reply #22 on: October 03, 2017, 03:40:04 PM »
I'm still watching from the wings!

Offline awemawson

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Re: Minnie on the cheap!
« Reply #23 on: October 03, 2017, 05:37:00 PM »
Always watching Norman, just not a lot to add  :med:
Andrew Mawson
East Sussex

Offline Pete W.

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Re: Minnie on the cheap!
« Reply #24 on: October 04, 2017, 07:54:25 AM »
Always watching Norman, just not a lot to add  :med:
 

Me too! 
Best regards,

Pete W.

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Offline chipenter

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Re: Minnie on the cheap!
« Reply #25 on: October 04, 2017, 11:59:11 AM »
I make my own gear cutters as horological cutters are £80 plus each , Doc did a video on making single point cutters slower but gentle on the machine .
Jeff

Offline NormanV

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Re: Minnie on the cheap!
« Reply #26 on: October 04, 2017, 12:04:24 PM »
It's reassuring to know that people are watching.
Now, to go back to my question. If I use single tooth cutters I will need to buy several to cover the range of sizes. If I use a hob, one size will cut all of the range of gears required. But, the hob is cutting more than one tooth at a time. Will the half HP motor on my mill have enough power to drive a hob?
Yes, I have considered making the cutter, in fact I would prefer to, but the cost of the materials makes it hardly worthwhile. One mistake, and I do make them, would make it cheaper to buy the ready made cutter in the first place.

Offline chipenter

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Re: Minnie on the cheap!
« Reply #27 on: October 04, 2017, 12:07:45 PM »
One point cutters are made from silver steel and hardened , cheep as chips just run slower .
Jeff

Offline NormanV

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Re: Minnie on the cheap!
« Reply #28 on: October 04, 2017, 12:30:21 PM »
25mm silver steel is £18 for 300mm, I don't think that is cheap. Plus I would have to buy silver steel and other steel to make the cutters to make the cutters.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #29 on: October 04, 2017, 12:32:55 PM »
I have made the blanks for all of the gears except the largest, I don't have any material for that. I have made them in brass as that is what I have.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #30 on: October 04, 2017, 12:37:32 PM »
I have also completed the smokebox and the perch bracket.
I bent the tube for the smokebox from 1.5mm sheet and welded the joint. That was a test for my welding, I initially burnt a hole in it but with a bit of practice I was able to weld a patch in it. It doesn't look too bad and anyway the perch bracket will cover it.

Offline awemawson

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Re: Minnie on the cheap!
« Reply #31 on: October 04, 2017, 12:49:08 PM »
Norman, do you know the DP and tooth counts - I'd assume that you probably do ?

Let me know and I'll sort through my collection - if I have what you need you can borrow them for the postage both ways.

(I have both conventional cutters and hobs)

Andrew Mawson
East Sussex

Offline eskoilola

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Re: Minnie on the cheap!
« Reply #32 on: October 04, 2017, 01:33:03 PM »
There is a downside in being on an assignment in Germany. Far away from home.
The upside is the weekly flea market. There is a guy who sells machining stuff with prises next to nothing.
I bought 4 kilograms of HSS blanks with 40 euros. They have some dirt on them but that is just cosmetics.

I will go there now on saturday and buy some more, wrap those into post packet and make You happy.
This assuming that the seller is on Lindleystraße. He is always on Schaumainkai but not always on Lindleystraße.
The flea market is alternating between those two locations.

They also sell decent sausages as my grandson demonstrates.



I'll put the pictures of the blanks here now on saturday if the seller was there.
http://www.hfm-frankfurt.de/flohm%C3%A4rkte.html

Offline NormanV

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Re: Minnie on the cheap!
« Reply #33 on: October 04, 2017, 02:40:03 PM »
Wow, there are generous people on this site! :mmr:
What I need is 20DP to cut 15,20,25,30,50 & 80 tooth gears. I think that single point cutters would be best with my milling machine.

Offline chipenter

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Re: Minnie on the cheap!
« Reply #34 on: October 04, 2017, 02:50:07 PM »
Make 20 dp single point cutters out of 1/4" silver steel , very much like a fly cutter only flat .
Jeff

Offline awemawson

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Re: Minnie on the cheap!
« Reply #35 on: October 04, 2017, 03:00:03 PM »
Norman, I have all sorts of B&S cutter sets but not 20 DP  :bang:

HOWEVER I do have  20 DP hob as per pictures. 3/4 bore weighs 400 grams
Andrew Mawson
East Sussex

Offline awemawson

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Re: Minnie on the cheap!
« Reply #36 on: October 04, 2017, 03:12:19 PM »
OK a bit more trawling through the hob drawers !

Turns out that I have two of the above hobs AND:

A nice little 10 mm bore one that I used to use with my Mikron gear hobber (which is for sale at £1000 if anyone wants it - needs a clean up as been in storage for 10 years)

This little one weighs in a 75 grams  :thumbup:
Andrew Mawson
East Sussex

Offline eskoilola

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Re: Minnie on the cheap!
« Reply #37 on: October 04, 2017, 03:32:48 PM »
How is that sort of gear tool used ?
Does it not need the gear rotation to be synchronized with the tool rotation ?
Is it self synchronizing - so as You start it it will automagically (somehow) catch the startpoint on correct phase?

I have seen many videos on people using thread cutter to make gear but nobody shows the very first round around - and nobody certainly shows how it goes all wrong.

And Yes - I know a lot more about datawarehousing than machining. That is the reason I am here - it is fachinating  :med:


Offline awemawson

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Re: Minnie on the cheap!
« Reply #38 on: October 04, 2017, 03:35:06 PM »
Andrew Mawson
East Sussex

Offline eskoilola

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Re: Minnie on the cheap!
« Reply #39 on: October 04, 2017, 03:48:58 PM »
Essentially yes:

https://en.wikipedia.org/wiki/Hobbing

In this case one thousand words had more information than one hour of tiresome hobbing videos.

Thanks !

Offline NormanV

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Re: Minnie on the cheap!
« Reply #40 on: October 04, 2017, 03:50:07 PM »
Am I missing something here? I read an article on making a hob to cut gears and it showed the teeth on the hob being cut straight. It was then used in steps to cut each tooth individually, but also cut a little of the following tooth and preceding tooth. In doing this it shaped the teeth correctly irrespective of the number of teeth on the gear.

Offline eskoilola

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Re: Minnie on the cheap!
« Reply #41 on: October 04, 2017, 03:52:10 PM »
I think that helix thing does exactly the same and in fact is more precise. However it needs a special machine to do the hobbing as it does not work in steps but continuously ... i think  :scratch:

The tool is most certainly NOT placed on 90/180 degree angle to get straight tooth.

Edit: Ärgh... In fact ... if I look the tool from side it actually looks like a lot of triangels. So it might actually BE placed on straight angle to get straight teeth....

Offline awemawson

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Re: Minnie on the cheap!
« Reply #42 on: October 04, 2017, 04:20:32 PM »
The hob rotates in synchronism with the blank at a ratio suitable to cut the right number of teeth. The hob is then transversed across the blank at a fixed cutting depth. Depending on materials it may take several passes at increasing depths before the full tooth form emerges
Andrew Mawson
East Sussex

Offline chipenter

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Re: Minnie on the cheap!
« Reply #43 on: October 04, 2017, 06:10:12 PM »
The hob is also at an angle to match the hobs pitch , you also can't start at the edge of the gear if trying to cut a gear being driven by the hob , I have tried this and bent the mandrill for my hob and totaled the gear .
Jeff

Offline NormanV

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Re: Minnie on the cheap!
« Reply #44 on: October 05, 2017, 11:41:17 AM »
I have been reading a copy of Model Engineer magazine from 1955 and I came across an article on gear cutting by Martin Cleeve. He said that in his early days he just bought a No 3 cutter and used it to cut gears from 25 to a rack with acceptable results. I might be able to get away with two cutters no3 and no 6. That's not so expensive!

Offline awemawson

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Re: Minnie on the cheap!
« Reply #45 on: October 05, 2017, 12:09:12 PM »
Norman,

I seem to recall that you said that this was a display model rather than a working one, in which case it doesn't matter a lot  :med:

Andrew Mawson
East Sussex

Offline NormanV

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Re: Minnie on the cheap!
« Reply #46 on: October 05, 2017, 12:46:16 PM »
Well I would like to run it on compressed air.

Offline eskoilola

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Re: Minnie on the cheap!
« Reply #47 on: October 07, 2017, 11:44:24 AM »
The dude who sells HSS steel blanks was not in the flea market today as I suspected. He will be in the other loaction next saturday.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #48 on: October 10, 2017, 03:35:24 PM »
I was busy over the weekend, I made the chimney. I cast a piece of aluminium using the lost foam method, what a lot of nasty fumes that produces! It was a terrible casting, barely big enough and full of bubbles. What the heck, it's going to be painted so I can use filler to hide the defects.
The chimney cap was fun, I made it from two pieces of 1/4" brass silver soldered together. I've finally worked out how to use my gas torch, outside of the furnace, without it blowing out. It was an interesting diversion from machining to work out the angles to rough out the two curves, my trigonometry tables from my school days came in handy for that.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #49 on: October 10, 2017, 03:41:19 PM »
I fabricated the chimney base rather than buying or making a casting, I was able to do it more quickly than it would have taken to make the pattern. I had to cut a large radius in the base of it and was rather pleased with my setup. I mounted it on a piece of angle on the faceplate, which needed counter balance weights to prevent vibration. I used my 1" square boring bar to hold the cutter, there were no problems with chatter. 

Offline eskoilola

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Re: Minnie on the cheap!
« Reply #50 on: October 14, 2017, 07:47:10 AM »
Nice setup for machining that curved surface.

I have now visited the flea market and the dude who sells all sorts of metal tooling stuff was indeed there.



I now could send You these HSS blanks as long as the weight is under 1 kilogram because then the posting fee is much lower. Weighting by hand ... maybe 4 pieces.

The HSS blanks are 200 x 15 x 15 millimeters in size.

If You want these just PM me  :borg:

Offline NormanV

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Re: Minnie on the cheap!
« Reply #51 on: October 18, 2017, 11:41:20 AM »
Here is progress so far, it is not fully assembled just propped up in the right places.

Offline NormanV

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Re: Minnie on the cheap!
« Reply #52 on: October 18, 2017, 11:46:57 AM »
Today I made a start on the brake and winding drums. The plans call for cast iron, I decided to cast aluminium blanks to make them.
I cast them in open top moulds. My sand is rather damp and when I poured the metal one of them boiled like a witches cauldron. Obviously that was a very damp bit of sand. You can see the difference in the appearance in the two photos. When I roughed them out I was expecting huge voids, but no, it's fine for the job.

Offline tom osselton

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Re: Minnie on the cheap!
« Reply #53 on: October 18, 2017, 07:22:50 PM »
It's coming along nicely!

Offline NormanV

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Re: Minnie on the cheap!
« Reply #54 on: October 22, 2017, 09:57:59 AM »
Thanks Tom.
I've machined the cable drum and the brake drum. I made the ratchet and pawl by careful marking out and filing, it wasn't worth setting up the milling machine and I get pleasure from making stuff by hand.
(the red spots are blood, I caught my finger on a burr, it was only a scratch but it wouldn't stop bleeding)

Offline NormanV

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Re: Minnie on the cheap!
« Reply #55 on: October 22, 2017, 10:08:02 AM »
I've also done the final drive gear with its centre. I was lucky to find a lathe change wheel of the correct DP and it was a simple job to machine it down to the correct thickness and bore it to size.
The keyways were a bit of a faff. I did them by putting a parting tool sideways in the lathe toolpost and racking it backwards and forwards taking a light cut each time. I tried it first on a piece of scrap, it was a hell of a struggle taking a lot of effort to pass the tool through the hole plus it kept digging in. I gave up and tried to make a broach, I tried to do it rough and ready and it was unsuccessful so I went back to the parting tool. After I had adjusted the gib strips it was better so I attacked the first keyway. It was still hard work but I got there. The second keyway was a doddle, I reduced the feed to one thou. for each cut and it sailed through, no dig ins. Well next mine I have to cut a keyway I'll know how to do it!
 

Offline awemawson

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Re: Minnie on the cheap!
« Reply #56 on: October 22, 2017, 10:47:00 AM »
When broaching keyways in the lathe I first turn up a peg that fits in the centre hole flush both sides. I then drill a hole that is slightly smaller diameter than the intended keyway at the intersection of the peg and the gear leaving a D shape in both.

Then removing the peg I broach away. This way there is much less material to remove and the hole tends to guide slender tools.
Andrew Mawson
East Sussex

Offline NormanV

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Re: Minnie on the cheap!
« Reply #57 on: October 22, 2017, 10:50:41 AM »
That's a good idea, I will file it away in my memory for the next time, thanks.

Offline tom osselton

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Re: Minnie on the cheap!
« Reply #58 on: October 22, 2017, 07:18:39 PM »
When I get a cut like that I put a piece of cigarette paper on it the blood holds the paper and drys like a second skin.
We learned to make keyways like that years ago in shop making a jackstand for a car it was external though down the side of the threaded rod. Its best to have a through hole though unless you have grooved the inside to clear the tail chip.