Machining Ally (LM25)

I have been working on a beam engine that I had cast from patterns I made last year. The original castings used Cast Iron and I produced a working engine and was happy. Unfortunately it was so heavy two men couldn't lift it. So I had the parts recast in Ally and started again, no problems with the 23 inch long beam, good casting and just a few holes to drill, likewise most of the other bits, "A" frames etc. However the cylinder block has me demented. I was going to machine it and fit a liner, but the machining has been a disaster. It looks like a ploughed field. Not joking, ruts up to 20 or 30 thou deep with lots od chatter. I tried different tools/tips/angles/speeds/fluid, all to no avail. However a foundry man told me that that was normal for this grade of metal castings and it needed heat treated . "Bung it in your gas oven" he said. Is this true and has anyone a more technical version of his comments. like temp / times / method of cooling. I would be greatfull if you have. Cheers John

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Google 'solution treatment' nothing to do with dipping in liquid, but all to do with modifying the grain structure of the alloy.


Reply to
Andrew Mawson

Ummm, not much of a surprise if it hadn't been heat treated. You can't machine raw aluminium castings. I'm kind of surprised you got as far as selecting an alloy grade and a foundry to cast it and never realised this. Raw cast alloy is like toffee.

You could do with a copy of "The Properties and Characteristics of Aluminium Casting Alloys" by Alcan Enfield Alloys if it's still available anywhere. Try Alcan I guess.

Anyhoo, looking in my copy. For fully heat treated condition LM25-TF heat the casting for 4-12 hours at 525C to 545C, quench in hot water followed by

8-12 hours at 155C to 175C and cool in air. It will then cut as clean as a whistle. Or just give it to a heat treatment company and let them slap it in with another batch.

No harm is done by exceeding the stated times so aim for the upper limits above for a big casting like yours.

Reply to
Dave Baker

You can get a copy of the old AlFed book here:

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Not quite as specific as the one Dave mentioned, but useful info on your subject from P64.

-- Richard

Reply to
Richard Shute

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