Quantitatively describing a small concavity

Don Y · 2017-04-20T00:02:35+00:00

I have a small (a few cubic inches) concave surface in (inflexible) plastic that I'd like to model, accurately (a few thousandths). What can I use to coat the (plastic) surface (think mold release) that won't damage/mar the plastic but will allow a flowable material to be introduced to that concavity, allowed to "set", then removed? What would be a good candidate for that "flowable material"? I'd like to be able to "machine" (some unspecified technology) the resulting "positive" extracted from the concavity.

Apr 20, 2017 23 Replies

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glen walpert 9 years ago

If it doesn't shrink (setting polymers, cooling wax) it will probably expand, such as various plasters and cements. In both cases, some have lower shrinkage (heavily reinforced fiberglass) or expansion, such as:

Gypsum Cements Hydrostone, Hydrocal and Ultracal 30 ceramicartsdaily.org/wp-content/uploads/2015/06/KnowYourPlaster.pdf

or "non-shrink" grouts, some of which are quite good.

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whit3rd 9 years ago

One possibility not yet mentioned, is electroplating; just brush with graphite, and electroplate up some copper. A trip to the freezer and the plastic will shrink and the copper will pop right off.

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