Article · Mold & Die
Choosing the Right Cutting Tool for the Mold Making Industry
Mold work splits into three jobs — pre-hard, annealed, and graphite — each with a right tool and a right tool path. A field guide to picking the cutter that pays dividends in finish and tool life.
Originally published in by Mike MacArthur, RobbJack
Choosing the right tool pays huge dividends in the quality, repeatability, and overall success of a mold job. Mold work breaks down into three distinct material situations — pre-hardened steel, softer annealed material, and graphite electrodes — and each rewards a different tool and tool path. Get the match right and the cut finishes clean, holds size, and lasts.
Pre-hardened steel (30–65 HRc): four tools, four jobs
- Ball end cutters — the primary choice for 3D cavity and core work. Run a constant-Z-level roughing routine, climb milling, 25–40% radial step-over. Take 10% of diameter per pass at 30–40 HRc, 5% at 40–50 HRc, and 4% above 50 HRc.
- Toroidal (corner-radius) tools — best for helical bores and ribs. Side step-overs of 5% (30–50 HRc) or 2% (above 50 HRc), with axial depth up to 1× the diameter per pass.
- Multi-fluted bull-nose — for wide-open areas with flat floors. Use trochoidal paths for slots, with the tool at about 50% of the slot width.
- Square end — reserve for finishing small radii only; it chips easily in pre-hardened material.
Softer material and graphite
In annealed material, modern CAD/CAM hybrid tool paths keep the angle of engagement constant through corners, which protects the edge and the finish. For graphite electrodes, diamond-coated tools are the standard — tool life runs 10 to 30 times longer than uncoated carbide, with diamond coatings available from 2 to 20 microns to suit the detail and abrasiveness of the job.
There's no universal mold tool — there's a right tool for pre-hard, for annealed, and for graphite. Matching the cutter and the path to the material is the whole game.
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