Chris Collins

Tools · casting

Resin casting calculator

Resin for parts cast in a mould — volume from a shape, an STL, water displacement or a fill test, minus inserts; polyurethane, epoxy, UV and polyester classes with A and B by weight and volume; cold casting with metal or stone powder by weight and by volume; fillers and pigment; per part, per batch, kits and cost per part; how many moulds one mix fills before it gels; cure time against temperature; exotherm and shrinkage checks; slush and rotational shells; and a printable plan.

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How to use it

This is for filling a mould with resin, many times over: how much to mix for each part and for a run of parts, what that costs, and whether it will get too hot. For epoxy river tables and big single pours use the epoxy pour planner or the resin pour calculator; for the mould, mould making and the mould maker. Jesmonite, plaster and concrete are in concrete casting; metal in the foundry calculator.

How to use it

  1. The part: a shape, an STL / OBJ / 3MF (its volume and surface area are read in the browser), the rise in a measuring jug when you sink the master (water displacement), or a fill test: fill the finished mould with water and measure it (1 g of water is 1 ml); rice works for moulds that must stay dry but reads 5–10 % low. Inserts and embedded objects are subtracted.

  2. The resin: classes with typical values — fast and 10-minute polyurethane, water-clear urethane, epoxy casting resin, deep-pour epoxy, UV resin and polyester with MEKP. Each has its mix ratio (by weight or volume — the other basis is worked out from the parts' densities), pot life, demould and full-cure times, the thickest section it will take in one pour, linear shrinkage and how much pigment it tolerates. Add your own resins; they stay in this browser.

  3. How it is cast:

    • Solid — with an optional filler (whiting, talc, microballoons, fumed silica) as a percentage of the resin weight; the filler takes up some of the volume, so the resin is reduced to match.

    • Cold cast — metal or stone powder stirred into the resin, usually 1:1 to 3:1 powder to resin by weight for metals. The tool gives the weights, the ratio by true volume (from the solid density) and the ratio measured loose in a cup (from the poured density), for the whole part or for a skin coat of a given thickness backfilled with plain resin.

    • Slush / rotational — a hollow part: surface area × shell thickness, in a number of coats.

  4. Batch and pours: parts wanted, moulds on hand and how long one takes to fill. It uses three quarters of the pot life to say how many moulds one mix can fill, and how big each mix should be.

  5. Temperature: pot life and cure times are scaled with the rule of thumb that reaction rate doubles every 10 °C. It is a rule of thumb, not a datasheet: below about 15 °C many resins never cure properly.

  6. Checks: the thickest section against the class’s limit (exotherm — heat that cracks, warps or yellows a part), shrinkage from a mould dimension to the part (and the mould size for a wanted part), and a pressure-pot note: about 40–60 psi (2.8–4 bar), and a mould poured under pressure must cure under pressure.

Print plan prints only the plan card; Copy as text copies it. Resin values are typical for the class, never a particular product — the product’s technical data sheet wins. Polyester and its MEKP catalyst need ventilation, a respirator and goggles.

Works in any current browser. Metric or imperial is shared with the other casting tools.

Sharing

Share link copies a URL that opens the tool as you have it set up (an STL travels only as its volume, area and size). Your own resins and saved recipes are never in a link.

Privacy

Nothing leaves your browser. Models are read locally; settings, saved recipes and your own resins are kept in this browser’s local storage.

Runs entirely in your browser; nothing you type leaves this page.