A centreless grinder grinds round parts without holding them between centres. The part rests on a work blade between a grinding wheel and a slower regulating wheel, which turns it and feeds it through. It is very fast for large batches of pins, rods and bushes.
Quick facts
- Holding
- Work blade between grinding and regulating wheels; no centres
- Typical diameter range
- About 3–80 mm (0.118–3.15 inch) on common machines
- Diameter tolerance
- About ±0.002–0.005 mm (±0.0001–0.0002 inch)
- Methods
- Through-feed (straight parts) and in-feed (shouldered or profiled parts)
- Best for
- Large quantities of round parts
- Not for
- Parts with flats, cross holes near the ends, or very short length-to-diameter
Through-feed or in-feed?
- Through-feed: straight parts pass continuously between the wheels; very high output for pins, rods and tubes
- In-feed (plunge): the part is placed in position and the wheels close in; used for parts with heads, shoulders or tapers
Typical parts
- Dowel pins, piston pins and rollers
- Bright bars and shafts
- Bushes and sleeves (outside diameter)
- Valve stems and plungers
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Questions
- Why is it called centreless grinding?
- Because the part is not held between centres. It is supported by a blade and turned by a regulating wheel, so no centre holes are needed.
- When is centreless grinding cheaper?
- For large quantities of plain round parts: parts feed straight through, often thousands per shift.
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 9 October 2026.