Cast white metal bearing advice needed.

This is the magneto drive shaft bearing off my Anzani engine.

The broken off bit is left hand thread. Needless to say when I removed the brass collar that was screwed on I didn't know it was left hand hence the break.😞

It is about 35 mm long and the diameter of the parallel bit is 20 mm approx and it carries a shaft 15mm diameter.

I need to make a replacement and I want to make it in a similar manner to the original. I know for a one off it probably makes sense to machine from solid or to machine one from a lump of bronze but I really want to make a casting and machine it.

I tried to make a silicone mould but it wasn't succesful for a variety of reasons the principal one beind difficulty of de-aerating the resin before it went off.

My proposed method is to make a two part mould out of a couple of chunks of ally that I have in stock.

I propose to spigot the two pieces of ally bar with a shallow spigot then bore one piece to make the parallel bit including a slight angle to permit separation from the mold, this will be through bored to allow molten metal to be poured into the mold.

The other half I intend to machine a triangular pocket to produce the flange and bore a recess to produce the tapered bit. I will add a short bit onto the taper for a chucking allowance.

The mould cavity will be carbon blacked to ensure release ( or would Zebrite work).

The two halves of the mould will be clamped together, preheated and the metal poured.

Simples.

Or is it? Any advice or suggestions will be great fully received.

Edited By ANDY CAWLEY on 26/10/2014 06:56:36

Oh, I forgot to say that I started this thread off 'cos I couldn't find any tool geometry, feeds and speeds data for machining white metal!

Is the original some form of white metal? hard to tell from the photo cast iron colour or is it bronze . should be possible to cast but would need the right alloy as some of the white metals are quite soft and that thread would be a weak point.

If bronze then I would machine off the parallel section, bore the tapered section and then silver solder in a new piece of bronze that could then be trued up, bored & threaded. If CI then does not look too hard to make from a bit of CI bar.

Try sealing the resin/rubber mixing container and leave a small hole to connect to a vacuum cleaner, this may be enough to degass the liquid. Also don't go mad whan mixing it which can induce air. Again when poured around the part see if you can arrange to use the vacuum to degass and pour it in gently like pouring a pint so you don't get a head on it.

Edited By JasonB on 26/10/2014 07:30:11

The original item is cast white metal and has lasted very well for 89 years. It's just me who is a clumsy b*st*rd that broke it.

As I said in my OP, of course, it would make sense to machine from solid but that is not what I want to do, I want to stick to original specification.

On the moulding rubber question I had a long conversation with some one who uses the very hard grade professionally and he told me that because of the very high viscosity of the un cured resin a very high vacuum is need to properly degass the mix. He also said it is impossible to avoid air entrapment and get a good mix.

So casting white metal it is then!!!!

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Recent thread

Andy, some of these apparent white metal castings are in fact high Zinc content, Turning them is a bit of a task as the metal turns black and sticks like chewing gum.

I would advise that you consider an alternative as White metal bearing materiel will be soft, also Mazak. A metal approaching they physical properties would be yellow brass if you can find some of the size you need. Otherwise cut from normal brass bar which would be better to machine. In fact I think you will find the original is a pressure die casting and almost impossible to duplicate easily.

Clive

Is it a 'cost no object' repair?

If so, google 'micro TIG welding' which appears to be able to repair almost any broken metal item because the weld pool can be reduce to a, literally, tiny spot.

Someone really good with access to a tiny oxy set may also be able to do it in multiple stages.

Neil