Honing uses bonded abrasive stones pressed outward against a bore, with a rotating and reciprocating motion that removes high spots and corrects the bore's geometry as well as its finish. Lapping runs fine loose or charged abrasive between the part and a lap of accurate form, removing very little material and producing extreme flatness and surface quality without correcting significant geometric error. One fixes shape; the other fixes flatness and finish.

Because the tool rotates and reciprocates at the same time, so the abrasive traces crossing helical paths. The pattern is functional: the grooves retain oil, which is essential for lubrication and running-in on cylinder walls, and the angle and depth are specified rather than incidental. Too smooth a bore does not hold oil; too coarse a pattern consumes oil and wears rings, so the cross-hatch is a controlled process output.

Taper, barrel and hourglass shapes, bell-mouthing at the ends, and out-of-roundness left by boring or by distortion during heat treatment or clamping. Because the stones bear over a long contact length, they cut where the bore is tight and pass over where it is open, converging on a straight round bore. It cannot correct positional error: a bore in the wrong place is honed into a better bore in the same wrong place.

When flatness and surface finish are the requirement and material removal is not: sealing and mating faces, valve seats and discs, gauge blocks and other reference surfaces, hydraulic spool and body faces, and optical components. It is the process used when parts must seal or contact over their full area, or when a surface must be brought to a finish that grinding cannot reach.

Critically in lapping. A single abrasive particle coarser than the lapping compound will scratch the surface across its whole travel, undoing the work, so laps, parts and the working area are kept scrupulously clean and different grades are never mixed. Honing is less sensitive but still depends on flushing swarf and abrasive debris away from the stones, since loaded stones stop cutting and start burnishing.

Portable and machine-mounted honing tools exist and are widely used for repair and small-quantity work, and they will improve finish and to some extent geometry. A dedicated honing machine controls stroke, speed, stone pressure and dwell far more precisely, which is what allows repeatable size and geometry in production. For engine and hydraulic cylinder work to specification, a purpose-built machine is normally required.

By expanding the stones progressively and measuring, either with in-process air gauging that feeds back to the machine or by stopping and checking with a bore gauge. Because removal is slow and controlled, honing can approach a final size gradually without overshoot, which is one of its advantages: a bore can be brought to a close tolerance with confidence rather than being cut to size in one pass.