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Machinable Wax??

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rklopp:
Watch the shrinkage. I tried to use commercial machinable wax to support machining a thin-wall brass part sort of like a 4” canoe. The wax shrank like mad, so that idea was a flop. I ended up using Wood’s metal.


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awemawson:
When I cast the 170 mm diameter blank for my chuck adaptor prototype I was getting about 10 mm shrinkage, ie shrank to 160 diam.

AdeV:
Most of my wax was made with a 4:1 ratio (4 pats wax, 1 part plastic) by weight. It shrinks like a bugger so make your mould oversized.

Once it's set, assuming you're machining the final thing to dimension, you'll be OK (dimensional stability is good with temperature, as far as I know)

Yes - definitely try 1 pour at a time, it doesn't like to stick to itself (because of the shrinkage, I think) if you pour it in multiple goes.

My first wax was made with melted candles + freezer bags from the local supermarket. Later wax blocks were made from scrap candle wax & raw virgin LDPE pellets. Any LDPE source will do. I made a very small test sample using HDPE too, which didn't seem to be any different to the LDPE version - so I guess you can use whatever is cheapest.

Most instructions say to add the LDPE slowly to the molten candle wax. I found it made no difference if you added it slowly, or in one go. Stirring can be harder if you add the plastic in one go...

The key thing is temperature: Don't let it get above about 200C (IIRC), because it'll start burning around that temp. Candle wax will catch at much lower temperatures, so as Andrew said, it's better to bring the temperature up slowly after about 90C. That said, I did mine in a tar boiler (the thing roofers use when doing felt roofs); not much temperature control there, and I only had one fire (easily put out by turning off the heat & putting the lid on to exclude oxygen).

Once the batch is ready, pour *immediately*. If it solidifies in the pot, it's an absolute bear to re-melt, as it's an amazing thermal insulator. I once tried to re-melt a ~1 cubic foot block, and never managed it (there was still a solid lump left after 8 hours in the pot). To re-use solidified wax, you really need to grate it into swarf first.

You will never get the pot clean again, so buying a dedicated pot is definitely a wise move. Remember you need a volume at LEAST 10% bigger (I'd got for 20%) than the final volume of your pour, to account for expansion in the molten phase; and also because you need to stir it quite hard. Definitely use a drill mounted paint stirrer to make your life easier!

HTH, sorry about the brevity, I'm running late & have to go home now! Good luck!

efrench:
Would polymorph plastic work? https://www.amazon.com/Polymorph-Plastic/s?k=Polymorph+Plastic

Brass_Machine:
Thanks Ade!

I appreciate the information.

Eric

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