Author Topic: Minnie on the cheap!  (Read 846 times)

Offline NormanV

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Global Moderator
  • Hero Member
  • *****
  • Posts: 5493
  • Country: gb
  • East Sussex, UK
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.

  • Hero Member
  • *****
  • Posts: 739
  • Country: gb
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.

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

Offline NormanV

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 451
  • Country: gb
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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.

  • Hero Member
  • *****
  • Posts: 739
  • Country: gb
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.

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

Offline NormanV

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Hero Member
  • *****
  • Posts: 1934
  • Country: gb
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.

  • Hero Member
  • *****
  • Posts: 739
  • Country: gb
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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

  • Sr. Member
  • ****
  • Posts: 492
  • Country: gb
  • United Kingdom
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 »