Precision Grinding: Surface, Cylindrical and Centerless

Which grinding does your part need?

Surface grinding makes a face flat and smooth with a rotating abrasive wheel (source 1): a fixture plate, a punch face, a parallel, a die shoe, anything that has to sit flat against another part.

Cylindrical grinding finishes an outside diameter with the part held between centers (source 2), and a shaft ground that way can hold its diameters concentric to one another (source 3). That makes it the route for a shaft with bearing journals, a stepped pin, or a print that ties the runout of one diameter to another.

ID grinding sizes a bore with a smaller wheel run inside it (source 2): the bore of a bushing that runs on a hardened shaft, a die button, a sleeve with a slip or press fit.

Jig grinding is for a hole or shape that needs both its size and its position: tool and die makers use it for jigs and for the mating holes and pegs on dies, and the handwheels index its axes to about 0.0001 in (source 4).

You do not have to name the process. The callouts on the print decide which grinding each feature gets.

When is centerless grinding the right process?

Centerless grinding holds the part on its own outside diameter: it rides on a work rest blade between the grinding wheel and a smaller, slower regulating wheel, with no centers, center holes or chuck, and it can improve the roundness of an out-of-round blank (source 5).

Through-feed, where the part passes straight between the wheels, suits straight cylindrical parts with no shoulders or other features in the way. In-feed, where the part stays put along its axis and is fed into the wheel, handles steps and more complex profiles, and end-feed is used for tapered parts (sources 5, 6). Centerless is the usual choice when many parts have to be ground in a short time (source 6), such as a lot of pins or rollers to one diameter.

For reference only, not a quoted figure: a Today’s Machining World profile of a centerless bar-grinding company reports holding 0.0002 in on bar diameter and 0.00005 in on roundness as routine (source 7). A centerless-ground diameter here is quoted to its callout on your print, like any other ground feature.

What tolerance can grinding hold?

For reference only, not a quoted figure: cylindrical grinding is normally held to ±0.0005 in on diameter, and precision work reaches ±0.00005 in (source 8). The bands for milled and turned features, before any grinding, are set out in CNC machining tolerances. ASME B46.1 defines roughness, waviness and lay and the parameters used to specify them (source 9), so the finish callout on your print uses those definitions.

The design review points out the callouts that drive the cost, so a tolerance tighter than the part needs can be opened up before you order.

Can hardened parts be ground?

Yes. Grinding is the established way to finish a part that is already in hardened steel: hard turning is often considered a replacement for it, but grinding holds roundness and cylindricity more accurately (source 10). That is why a punch in hardened tool steel gets its body and point ground. Hardness verification can be arranged and quoted when the print requires it; it is not routine.

What does grinding do for a pin?

It finishes the working diameter. On a dowel, locating or ejector pin, grinding brings that diameter to the size and tolerance, or the fit, on your print. A custom size, length or end is quoted from the print; pin types, fits and materials are covered on shafts and pins.

Gage pins and plug gauges are quoted to the class on your print. The classes, and when a pin is plus or minus, are explained on custom gauges.

What should I send for a grinding quote?

Send a drawing with a callout on every ground feature: the size and its tolerance, or the fit and the part it mates with; roundness or cylindricity; flatness and parallelism; runout to a named datum; and the finish. Add the material and hardness and any finish. Ask for more than one quantity, such as 1, 25 and 100, and the quote shows each.

Rush 1-2 weeks applies to machined parts with no secondary operations. Heat treat, grinding, EDM and finishing add time, and the quote gives the real date. Lead time starts at order approval. Put your need date in the part description and the quote answers it.

A pin or bushing with no drawing can start a one-off quote from a new sample part; turning it into a drawing is reverse engineering, quoted as its own line. The sample ships back with the parts.

Sources

All accessed 27 September 2026. Where a figure here differs from your print, the print governs.

1. Wikipedia, "Surface grinding": en.wikipedia.org/wiki/Surface_grinding (an abrasive wheel makes a face flat; magnetic chuck, or vacuum and mechanical holding; aluminum, stainless, brass and some plastics).

2. Wikipedia, "Cylindrical grinder": en.wikipedia.org/wiki/Cylindrical_grinder (work held between centers; ID grinding with a smaller wheel).

3. MMS Editorial Team, "Grinder Offers Precise, Single-Setup Production", Modern Machine Shop, 11 April 2012: mmsonline.com/articles/grinder-offers-precise-single-setup-production (a shaft held between centers with nine ground diameters held concentric diameter to diameter).

4. Wikipedia, "Jig grinder": en.wikipedia.org/wiki/Jig_grinder (jigs and the mating holes and pegs on dies; handwheels index the axes to about 0.0001 in).

5. Chris Koepfer, "Centerless Grinding: Not Magic!", Modern Machine Shop, 15 December 2000: mmsonline.com (work rest blade and regulating wheel; no centers or center holes; thrufeed and infeed; improves roundness).

6. Wikipedia, "Centerless grinding": en.wikipedia.org/wiki/Centerless_grinding (in-feed and end-feed; many parts in a short time).

7. Today’s Machining World, "How It Works: Centerless Grinding", February 2006, updated 23 May 2022: todaysmachiningworld.com (a centerless bar-grinding company’s routine 0.0002 in on bar diameter and 0.00005 in on roundness).

8. Wikipedia, "Grinding (abrasive cutting)": en.wikipedia.org/wiki/Grinding_(abrasive_cutting) (cylindrical grinding diameter figures).

9. ASME B46.1-2019 (R2026), "Surface Texture (Surface Roughness, Waviness, and Lay)": asme.org (roughness, waviness, lay and their parameters).

10. Chris Koepfer, "Hard Turning as an Alternative to Grinding", Production Machining, 22 January 2010: productionmachining.com (hard turning is often considered a replacement for grinding; grinding holds roundness and cylindricity more accurately).