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Materials · Other materialsintermediate~2 min read

Foam, epoxy and solid surface

Short answer

Foam cuts almost effortlessly and the only real problems are holding it down and the mess. Epoxy machines like a hard plastic and produces dust you do not want to breathe. Solid surface machines beautifully and is abrasive on tooling.

Foam

Rigid insulation foam, EVA, and purpose made tooling board. They cut so easily that cutting forces stop being a constraint at all, which changes what matters:

  • Holding it down is the whole problem. Foam is light, so vacuum barely grips it, tape peels it, and clamps crush it. Double sided tape on a flat backer, or pins in waste areas, are the usual answers.
  • The mess is remarkable. Foam dust is light, static charged, and gets everywhere. Extraction is not optional if you like your shop.
  • Melting. Some foams melt from friction. Single flute bits, fast feeds, moderate RPM.
  • Surface finish. Open cell foam never cuts crisply. Closed cell tooling board can hold surprisingly fine detail.
  • Speed. You can usually feed as fast as the machine will physically move.

Foam is excellent for prototyping a 3D carve before committing expensive wood, for moulds and plugs, and for props and signage.

Epoxy and cast resin

Machining cured epoxy, including the resin sections of a river table, behaves like cutting a hard, brittle plastic.

  • It chips at edges rather than tearing. Sharp tools, light finishing passes.
  • Heat softens it, and softened epoxy gums the bit. Keep the chips moving.
  • The dust is fine and worth avoiding. Cured epoxy dust can be a sensitiser. Extraction and a respirator.
  • Wood and resin cut differently in the same pass, which is the specific challenge of flattening a river table. The bit alternates between two materials with very different hardness, and any deflection shows up as a step at the boundary. Light passes and a sharp surfacing cutter.
  • Polishing. A machined epoxy surface sands and polishes to clarity through progressive grits. That is the finishing process, not a machining one.

Solid surface (Corian and similar)

An acrylic or polyester resin filled with mineral powder. It was designed to be machined, and it shows.

Machines
Very predictably. No grain, no tearout.
Detail
Holds fine detail and V-carving extremely well
Tooling
The mineral filler is abrasive. Bits dull faster.
Dust
Fine mineral dust. Extraction and a respirator.
Cracking
Sharp inside corners concentrate stress. Add radii.

Offcuts from countertop fabricators are often free or cheap and make excellent material for signage, inlay and awards. It sands and polishes to any sheen you like, and it can be seam-glued invisibly with the manufacturer's adhesive.

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