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Old 17th Jan 2010, 7:02 pm   #17
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

In theory, I suppose it might be - but you'd run up against loss of detail and the problems of heat damage to the 'coating' if moulding with meltable compounds and the difficulty of removal of the extra layer from the original afterwards.
The amount of shrinkage isn't that great, usually. Many moulding and casting processes have a built-in degree of enlargement to compensate for shrinkage. In the case of radio knobs, provided the shrinkage is even over a batch of mouldings, it won't be important.

Plastics will sometimes continue to shrink slightly for years; the American Catalin castings can be found to have quite a large amount of shrinkage, which may be the result of poor storage, UV light etc. Bakelite doesn't seem to suffer from the same problem, though it can gradually - almost imperceptibly - distort over the years.
-Tony
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