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Old 17th Jan 2010, 11:38 am   #14
Aerodyne
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Join Date: Jun 2004
Location: Hampton Vale, Peterborough, UK.
Posts: 1,698
Default Re: Copying a control knob by moulding

Ben, some shrinkage is unavoidable and of course, it shows more the smaller the original knob is. The shrinkage occurs most during the casting process but adding fillers to the resin does, apparently, reduce the effect.
Much depends upon the final spacing of the knobs as, well apart, slight differences are not as apparent as wehen the knobs are close together.

I should also point out that Alginate isn't recommended for use with resins but when only one or two castings are required, I find it works well. It does tend to 'sweat' water and GENTLE application of warmth to the mould immediately before pouring the resin is one way to minimise water ingress.

The best way is of course to use hot-melt materials when copying heat-resistant items such as Bakelite knobs, or alternatively Latex, but these are much more involved and time-consuming and also rather more expensive.
-Tony
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