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Minnie on the cheap!

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NormanV:
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.

NormanV:
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!

NormanV:
The location bumps were cut freehand with a ballend mill.

awemawson:
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)

Pete W.:
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. 

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