Silicone and urethane mould making
How much rubber a mould takes — one- and two-part block moulds, cut moulds, brush-on glove moulds and poured blanket moulds, from the part's size, a shape or an STL — with A and B by weight and volume, pot life and demould times, an inhibition checker, release agents for each pair of materials, degassing and pressure notes, mother mould materials, and a printable step list.
Added
Works with
- Mold maker CNC and 3D printingprints the mould box — or the master itself, with no original — for the rubber worked out here
How to use it
I wrote this for the bit before casting: how big to make the mould box, how much rubber to buy and mix, and what is going to stop it curing. Pick the part, the kind of mould and the rubber, and it works out the rest. For the printable mould itself — parting lines, keys, sprues and a box you can 3-D print — use the mould maker. For what goes into the finished mould, see resin casting, concrete, plaster and Jesmonite and candles and soap; metal goes to the foundry calculator.
How to use it
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The part: a simple shape (box, cylinder, sphere, dome, cone), an STL / OBJ / 3MF file (read in the browser for its volume, surface area and size — the STL viewer shows more), or measured by hand: its size, its volume by water displacement and, if you know it, its surface area.
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The mould:
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One-part block — part glued to the base board, rubber over it. Box inside = part + 2 × wall, height = part + the rubber over the top. Rubber = box − part.
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Two-part block with keys and cut mould — rubber on every side, so the box also has rubber under the part. The tool suggests a number and size of registration keys for the parting line.
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Brush-on (glove) — rubber = surface × thickness. One thin unthickened print coat, then thickened coats of about 1.5 mm each until you reach the thickness; it reports the coats and the thickener.
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Poured blanket — a clay layer the thickness of the rubber, a mother mould over it, then the clay out and the rubber poured into the gap; the clay you need equals the rubber.
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Brush-on and blanket moulds need a mother mould: plaster bandage (area × layers × overlap, in rolls), a Plasti-Paste type thickened resin, fibreglass mat and resin, or a plaster shell.
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The rubber: the list has generic categories with typical values — platinum silicone at Shore 10A to 40A, tin silicone, urethane rubber 30A and 60A, alginate, latex and Oogoo. Mixed weight = volume × the mixed specific gravity; A and B are given by weight and by volume whichever way the product is specified. Add your own products (ratio, specific gravities, pot life, demould time) and they stay in this browser.
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Inhibition and sticking: tick everything the rubber will touch. Platinum silicone is stopped by sulphur clays, latex gloves, tin silicone, uncured 3-D printing resin and some paints and adhesives; urethane rubber bonds to porous surfaces and to itself and hates moisture. The release table covers each mould material against each cast material — silicone on silicone always needs a release.
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Print plan prints the plan card on its own; Copy as text puts it on the clipboard. Save keeps a recipe in this browser.
The numbers for each rubber are typical values for that kind of product, not any one brand. Your product’s technical data sheet wins — especially the mix ratio and whether it is by weight or by volume.
Degassing: rubber rises four to five times in a vacuum before it collapses, so the container must be four to five times the mix. Pressure: a pot at 40–60 psi (2.8–4 bar) crushes bubbles instead of removing them, so anything poured under pressure must cure under pressure. Use a pressure pot rated for the job.
Works in any current browser. Units (metric or imperial) are shared with the other casting tools.
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