Abrasive stones mounted on a rigid, reciprocating head remove stock and lay down the crosshatch that holds oil against a moving piston. When the drawing calls for a size, a straightness and a surface texture that a burnish cannot produce, honing is the finishing step.
A honing head carries 3–8 bonded abrasive stones (the “tool”) that are expanded against the bore wall under controlled pressure. The head simultaneously rotates and reciprocates, so each stone cuts on both the up and down stroke. The intersection of the two motions leaves the characteristic crosshatch pattern — not a defect, but the surface texture that lets a seal or piston retain an oil film.
| Variable | Typical value | Notes |
|---|---|---|
| Surface speed | 25–60 m/min | Stone contact speed; lower for hard materials |
| Reciprocation stroke | 30–50 m/min | Overlap of strokes sets the crosshatch angle |
| Stock removal | 0.01–0.2 mm | Typical final-pass allowance |
| Stone pressure | 5–20 bar oil pressure | Too high burns, too low glazes the stone |
| Coolant | Oil or honing oil | Flushes grit and carries heat away |
SRB is faster and leaves a low-friction burnished bore; honing leaves a crosshatch that retains oil and can fix more bore error. The choice is usually set by the print.
| Requirement | Honing | Skive & Roller Burnish |
|---|---|---|
| Oil-retention crosshatch | Yes — 30–45° lay | No — bright, smooth surface |
| Blind-end bore | Yes | No (needs tool exit) |
| Fixing taper / straightness | Good | Limited |
| Cycle time on long bores | Slower | Much faster |
| Surface work-hardening | Some | Strong (burnished) |
Rigid honing heads (used on honing machines with a spindle) hold the stones on shoes or wedge expanders and can correct geometry. Flexible / floating heads follow the existing bore and only smooth it. Stone grit is the main lever:
| Grit | Finish achievable | Use for |
|---|---|---|
| 80–120 | Ra 0.8–1.6 μm | Stock removal, roughing |
| 220–320 | Ra 0.2–0.6 μm | General finishing |
| 400–600 | Ra 0.05–0.2 μm | Mirror finish, seal surfaces |
| Diamond / CBN | — | Hardened steel, carbides, superalloys |
Bond choice (vitrified, resinoid, metal) matters more than grit for hard or sticky materials. For Inconel and hardened steel, diamond or CBN stones with a softer bond outlast aluminum-oxide stones by an order of magnitude.
Drill or SRB the bore to within 0.05–0.15 mm of final size. Honing is a finishing process, not a roughing one.
On a honing machine the spindle axis defines straightness — align to the bore with a dial or laser.
Coarse stones, moderate pressure. Check size every few passes with a bore gauge.
Finer stones at lower pressure to set texture and final size. Air-gauge or air-ring to verify.
Break the entry edge of any cross-passage; loose grit and chips must be flushed before assembly.