A jig grinder grinds holes, pockets and contours in hardened parts at very exact positions. A small, very fast grinding spindle orbits inside the hole while the table moves to each position. Toolrooms use it to finish press tool dies, punch plates, moulds and gauges after hardening, when hole sizes and positions must hold within a few microns.
Quick facts
- Main use
- Holes and contours in hardened steel and carbide
- Position accuracy
- About 1–3 µm on good machines
- Hole size accuracy
- About 1–2 µm
- Spindle speed
- Up to about 40,000–175,000 rpm (air or electric)
- Motion
- Spindle orbits (planetary) plus up and down stroke
- Control
- Manual co-ordinate or CNC contouring
Main parts
- Very rigid column and co-ordinate table
- High-speed grinding spindle in a planetary head
- Vertical stroking (chopping) for long holes and contours
- Precision scales and temperature-controlled setup
- Small grinding wheels and mounted points, diamond or CBN for carbide
- Optional C-axis for angled contours
Jig grinding or wire-cut EDM?
| Jig grinding | Wire-cut EDM | |
|---|---|---|
| Surface finish | Better, ground | Good, needs skim cuts |
| Hole roundness | Best | Good |
| Sharp inside corners | Limited by wheel size | Small corner radius |
| Typical role | Finishing precise holes after hardening | Cutting profiles in hardened plate |
Good to know
- Room temperature must be steady for micron accuracy
- Parts are usually hardened and stress free before jig grinding
- Many toolrooms wire cut first, then jig grind critical holes
- Inspection on a CMM confirms positions
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Questions
- What is a jig grinder used for?
- Finishing precise holes and contours in hardened parts: die and punch plate holes, guide bushes, gauge holes and mould parts.
- How accurate is a jig grinder?
- Good machines position holes within about 1–3 µm and size them within about 1–2 µm, in a temperature-controlled room.
- Why not finish the holes before hardening?
- Hardening moves and distorts parts. Grinding after hardening puts the holes exactly where they need to be on the finished hard part.
The figures on this page are typical values for guidance, written by Diemeco from standard engineering practice. They are not a specification: confirm grades and properties with the relevant standard or the supplier's mill test certificate, and tolerances with your workshop. Last checked 22 October 2026.