Re: casting wax

From: Bruce E. LeMaster (
Date: Fri Jun 11 1999 - 21:25:09 EEST

Glyn and all,

We did take into account the shrinkage of the wax and the casting when
building our SL patterns. The final castings came back well within
expected tolerances for cast parts. We did leave machine stock on the
parts so that we could finish machine the critical areas. Although we
didn't do a "scientific study" on accuracy, we found that the wax
patterns we produced were consistently within 0.005" on the dimensions
that we were interested in.

The big problem we had early on dealt with contricity of the parts. If
you look at the pictures you can see that we had a "rod" sticking off
the top of the domed piece to allow for gripping in the final machining
operations. During the demold of the first several parts (while the wax
was still warm) we were inadvertently warping the "rod." It was a very
little amount but it was enough to cause wobble when the castings were
chucked up to turn the machine stock off. We made some changes to our
process to ensure that the wax was firm before demolding. The final
parts did not have the same problem.


Bruce E. LeMaster

Glyn Churchman wrote:

> To add to Bruce's previous posting:
> As noted, the process works fine but your problem will be that the
> parts you cast in this silicone mold
> will be too small unless tolerances don't matter. Wax shrinks quite a
> bit.
> Many waxes will work but to get consistent dimensional results you
> must have good repeatability
> of the injecting pressure, temperature of the wax and temperature of
> the mold-- just as in
> injection molding of plastics. Depending on your part configuration
> some waxes may be too
> brittle or too soft.
> Glyn@Prototech, Inc.

Applied Rapid Technologies Corporation
265 Cambridge Street, Suite 100
Fredericksburg, Virginia 22405
(540) 371-1100 / (540) 371-4100 fax

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