Centreless grinding finishes round parts without holding them between centres. The part rests on a work blade between a fast grinding wheel and a slower regulating wheel that turns and feeds it. It is fast and very accurate for pins, rollers, rods and bushes made in large numbers.
Quick facts
- Diameter tolerance
- About ±0.002–0.01 mm (±0.0001–0.0004 inch)
- Roundness
- A few microns on good machines
- Surface finish
- About Ra 0.2–0.8 µm
- Through-feed
- Plain cylinders pass straight through, very fast
- Infeed (plunge)
- Parts with steps, heads or tapers
- Usually priced
- Per piece, depending on stock removal and quantity
Through-feed or infeed?
| Through-feed | Infeed (plunge) | |
|---|---|---|
| Part shape | Plain cylinders: pins, rods, rollers | Shoulders, heads, tapers, forms |
| Speed | Very fast, continuous | One part at a time |
| Wheel | Straight | Dressed to the part's profile |
Good to know
- No centre holes needed, so short pins and long bars are both easy
- Leaves about 0.1–0.3 mm (0.0039–0.0118 inch) on diameter for grinding
- Hardened parts are ground after heat treatment
- Roundness depends on setup height; lobing can occur if set badly
- Bars up to several metres can be ground through-feed
What to tell the grinder
- Material and hardness
- Finished diameter and tolerance, roundness and Ra
- Stock left on diameter
- Length and any shoulders or tapers
- Quantity per batch
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Questions
- Centreless or cylindrical grinding?
- Centreless is faster and cheaper for plain round parts in quantity. Cylindrical grinding between centres is better when diameters must be concentric to centre holes or when there are many shoulders and faces.
- What tolerance can centreless grinding hold?
- Diameter within a few microns and roundness of about 1–3 µm on a well-set machine, with surface finish around Ra 0.2–0.4 µm.
- Can centreless grinding remove a lot of material?
- It is meant for finishing. Leave about 0.1–0.3 mm (0.0039–0.0118 inch) on diameter; more stock needs several passes and costs more.
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 16 October 2026.