Grinding, Sanding and Polishing
Grinding, sanding and polishing remove a thin layer of material with bonded or coated abrasive to correct form or improve surface finish.
- Part
- Finishing
- Variants
- 4
- Revised
- 2026-08-11
At a glance
- Family
- Subtractive
- Typical tolerances
- Surface and cylindrical grinding ±0.0001–0.0005 in (±0.0025–0.013 mm); honing corrects bore geometry within a few tenths; lapping holds flatness to a few millionths of an inch
- Surface finish
- Grinding 8–63 µin (0.2–1.6 µm) Ra; honing 4–32 µin (0.1–0.8 µm); lapping 1–16 µin (0.025–0.4 µm); superfinishing and polishing 1–8 µin (0.025–0.2 µm)
- Typical volumes
- 1 to millions of parts; centerless and production grinding lines run continuously
- Lead time
- 1–10 business days at a job shop depending on setup complexity; production grinding runs in seconds to minutes per part
- Materials
- Metal, Plastic, Wood, Glass, Ceramic, Composite
What it is
Grinding, sanding and polishing remove material with bonded or coated abrasive to correct form, hold tight size, and reach surface finishes that cutting tools cannot. The family spans a wide range of removal rates and results: surface and cylindrical grinding hold ±0.0001–0.0005 in (±0.0025–0.013 mm) and produce 8–63 µin (0.2–1.6 µm) Ra; honing corrects bore geometry at 4–32 µin (0.1–0.8 µm); lapping reaches 1–16 µin (0.025–0.4 µm) with flatness measurable in light bands; polishing and superfinishing go below 8 µin but correct no geometry at all.
Grinding is also the only practical way to machine material above roughly 60 HRC, which is why hardened parts are ground after heat treatment rather than cut. The distinguishing constraint for a designer is that abrasive processes need access, relief and stock: a wheel has to reach the surface, run out somewhere, and have 0.005–0.020 in (0.13–0.5 mm) of material to remove.
How it works
- Leave grind stock. Parts are machined oversize before heat treatment. Typical allowance is 0.010–0.020 in (0.25–0.5 mm) per surface where distortion and scale must be cleaned up, and 0.005 in (0.13 mm) or less where only a finish pass is needed. Too little stock leaves black spots; too much wastes cycle time and risks thermal damage.
- Select the abrasive. Aluminum oxide for steels, silicon carbide for cast iron and non-ferrous metals, CBN for hardened steels and superalloys, diamond for carbide, ceramics and glass. Wheel specification also covers grit size (roughly 36–600), grade (bond hardness) and structure.
- Grind. Conventional vitrified wheels run at roughly 5,500–6,500 sfpm (28–33 m/s); superabrasive wheels run considerably faster. Depth of cut is typically 0.001–0.003 in (0.025–0.075 mm) for roughing and 0.0002–0.0005 in (0.005–0.013 mm) for finishing, followed by spark-out passes at zero infeed to let the machine settle to size.
- Manage heat. Grinding puts nearly all its energy into the workpiece as heat. Excessive rates cause grinding burn — local retempering, softening, tensile residual stress and in severe cases surface cracks. Flood coolant, correct wheel dressing and conservative infeed are the controls; nital etch and Barkhausen noise inspection are how burn is detected.
- Dress the wheel. A loaded or glazed wheel cuts by rubbing, which generates heat instead of chips. Regular dressing with a diamond restores sharp cutting points and the wheel's form.
The specialized operations
Honing uses expanding abrasive stones in a reciprocating, rotating tool to correct bore roundness, straightness and taper — removing 0.0005–0.010 in (0.013–0.25 mm) — and leaves the cross-hatch pattern that retains oil in cylinder bores. Lapping rubs the part against a soft plate charged with loose abrasive, removing 0.0001–0.0005 in (0.0025–0.013 mm) and producing exceptional flatness on seal faces and gage surfaces. Belt sanding and polishing conform to contours and produce appearance finishes, but they follow the existing form rather than correcting it — a polished part is a smoother version of whatever shape it already was.
Design guidelines
Provide wheel relief at every shoulder
A grinding wheel cannot cut into a sharp internal corner; its own edge breaks down and the corner ends up radiused and out of tolerance. Design an undercut or relief groove at the shoulder — typically 0.030–0.060 in (0.75–1.5 mm) wide and at least as deep as the grind stock — wherever a ground diameter runs into a face.
Prefer through features to blind ones
Through-grinding a bore or a slot is straightforward; blind bores require the wheel to reverse inside the feature, which limits the achievable finish and size control near the bottom. The same applies to honing.
Specify the loosest finish that works
Each step down the finish scale costs disproportionately. Finishes tighter than about 63 µin (1.6 µm) Ra usually require a dedicated grinding operation, and below about 32 µin (0.8 µm) a secondary lapping or polishing operation. Use the surface finish chart to match the callout to what the process actually delivers rather than defaulting to a tight number.
Do not ask polishing to fix geometry
Polishing, buffing and belt sanding remove the peaks of the existing surface. They cannot correct flatness, roundness, parallelism or a dimension, and on a machined part they will round edges and blur detail. Where both form and finish are required, grind for form and then polish for appearance.
Specify Rz as well as Ra on critical surfaces
Ra averages the whole profile and is insensitive to isolated deep scratches; Rz is peak-to-valley and is not. A ground sealing face can pass an Ra spec and still leak because of one deep scratch. For seal lands, fatigue-critical surfaces and bearing journals, specify both.
Allow for distortion and support
Thin, long or unsupported parts deflect under wheel pressure and spring back out of tolerance. Provide clamping surfaces, center holes, or steady-rest locations, and expect that a thin part may need multiple spring passes.
| Feature | Recommended | Limit | Why |
|---|---|---|---|
| Grind stock allowance | 0.010–0.020 in (0.25–0.5 mm) per surface | 0.005 in (0.13 mm) finish only | Too little leaves unground low spots |
| Shoulder relief groove | 0.030–0.060 in (0.75–1.5 mm) wide | Required at every ground shoulder | Wheels cannot cut a sharp internal corner |
| Grinding tolerance | ±0.0005 in (±0.013 mm) | ±0.0001 in (±0.0025 mm) | Tighter needs temperature control and slow finishing |
| Ra by operation | Grinding 8–63 µin; honing 4–32 µin; lapping 1–16 µin | Polishing < 8 µin, no form correction | Each stage trades removal rate for finish |
| Finishing depth of cut | 0.0002–0.0005 in (0.005–0.013 mm) | — | Heavier cuts risk grinding burn |
| Critical surfaces | Specify Ra and Rz | — | Ra alone hides isolated deep scratches |
Cost drivers
Abrasive finishing is priced by machine time, and machine time is driven by how much material has to come off and how tight the result must be.
- Stock to remove. Grinding removes material slowly compared to milling or turning. Every extra thousandth of allowance is cycle time, so leave what the process needs and no more.
- Finish requirement. Cycle time rises sharply below about 63 µin (1.6 µm) Ra, and a callout below 32 µin (0.8 µm) usually adds an entire secondary operation.
- Setup and fixturing. Grinding setups are precise and slow to establish. Cost per part falls dramatically with lot size; one-off grinding is dominated by setup.
- Wheel and dressing consumption. Superabrasive CBN and diamond wheels are expensive but last far longer and hold form, so they win on volume and lose on short runs.
- Inspection. Tight tolerances require temperature-stabilized inspection, and burn-sensitive parts require nital etch or Barkhausen testing per lot.
Cost-reduction tactics:
- Grind only the surfaces that need it. A drawing that calls out a ground finish on every face doubles or triples cost for no function.
- Specify Ra to the function, not to the shop's best capability.
- Design relief grooves and through features so the operation is a single straightforward pass.
- Consider hard turning instead of cylindrical grinding on hardened parts where ±0.0005 in and 32 µin are adequate — it is often faster.
- Where the requirement is only deburring and edge break rather than form correction, price vibratory finishing against hand or machine grinding.
Variants
4 named
Wheel Cutting
Belt Sanding
Honing
Lapping
Questions
6 questionsWhat surface finish can grinding achieve?
Surface and cylindrical grinding typically produce 8–63 µin (0.2–1.6 µm) Ra. Honing reaches 4–32 µin (0.1–0.8 µm), lapping 1–16 µin (0.025–0.4 µm), and superfinishing or polishing below 8 µin (0.2 µm). Each step down trades removal rate and cost for finish.
How much stock should I leave for grinding?
Typically 0.010–0.020 in (0.25–0.5 mm) per surface where heat-treat distortion and scale must be cleaned up, and 0.005 in (0.13 mm) or less for a finish pass only. Too little leaves unground low spots; too much is wasted cycle time and raises the risk of grinding burn.
Why does a ground shoulder need a relief groove?
A grinding wheel cannot cut into a sharp internal corner — its edge breaks down and the corner ends up radiused and out of tolerance. An undercut 0.030–0.060 in (0.75–1.5 mm) wide and at least as deep as the grind stock gives the wheel somewhere to run out.
What tolerance can grinding hold?
±0.0005 in (±0.013 mm) is routine for surface and cylindrical grinding, and ±0.0001 in (±0.0025 mm) is achievable with temperature control, careful spark-out and slow finishing passes. Jig grinding and lapping go tighter still, at correspondingly higher cost.
Can polishing fix a flatness or roundness problem?
No. Polishing, buffing and belt sanding remove the peaks of the surface that already exists — they follow the form rather than correcting it, and they round edges and blur detail. Grind or lap for form, then polish for appearance.
What is grinding burn and how is it detected?
Grinding puts almost all its energy into the workpiece as heat, and excessive removal rates locally retemper the surface, leaving softened material and tensile residual stress that shortens fatigue life. It is controlled with flood coolant, correct wheel dressing and conservative infeed, and detected by nital etch inspection or Barkhausen noise measurement.