GlossaryKind of term: Manufacturing termHoning
What is honing?
Honing is a finishing process for bores in which abrasive stones rotate and stroke at the same time, improving size, form and roughness.
Honing is a bonded-abrasive finishing process, mainly for bores. A honing head carrying abrasive stones or diamond sticks rotates and strokes back and forth in the bore while the stones are expanded outwards. This leaves a cross-hatch pattern in the wall. Honing removes little material and improves the size, roundness, cylindricity and roughness of a bore that is already close to size. Typical applications include hydraulic cylinders, valve bodies, cylinder liners and bearing bores.
What decides the result of honing?
The result depends on abrasive grit and bond, expansion pressure, the ratio of stroke speed to rotational speed, stroke length and overrun at the ends, the honing oil and the condition left by the previous operation. The ratio of stroke to rotation sets the cross-hatch angle; in a cylinder wall that pattern retains oil. With a floating tool or a floating workpiece the honing head follows the axis of the existing bore: form errors such as barrel shape, taper and out-of-roundness are reduced, but the location of the axis hardly changes. A blind bore needs an undercut at the bottom or an adapted stroke, because otherwise the stones cannot cover the end fully.
How does honing work in practice?
The previous operation leaves a small allowance, agreed with whoever does the honing. Many shops have no honing machine; the part then goes to a specialist, with transport, lead time and a price per part or per bore. A tight cylindricity also needs a form measurement along the length of the bore, on a form measuring machine or a scanning coordinate measuring machine; a bore gauge gives two-point sizes, not cylindricity. Whether a bore needs honing usually becomes clear from the combination of form tolerance, roughness and function, such as a piston or seal; where the drawing carries that combination, the route often gains an operation.
What is honing often confused with?
Honing is not internal grinding: in internal grinding the machine controls the wheel path, so the location and orientation of the bore can still be corrected; a floating honing head follows the existing axis. Roller burnishing removes no material but flattens the peaks of the profile, improving roughness rather than form. Lapping works with loose abrasive instead of bonded stones.
How do you see honing in Blake?
In Blake the tolerances and roughness of the bore sit with the part as proposals from the drawing; you confirm or correct them, and who did so and when stays visible. Subcontracted honing appears as its own line in the estimate from your subcontract library; a missing price leaves the line open. More on estimating.
Frequently asked questions
When does a bore need honing?
When the cylindricity, roundness or roughness required goes beyond what drilling, boring or turning holds reliably, or when a piston or seal runs in the bore. Where that limit lies depends on machine, diameter, length and material.
Does honing correct the position of a bore?
Not in any meaningful way. A floating honing head follows the existing axis and improves size, form and roughness. Location and perpendicularity must already be within tolerance after boring; otherwise internal grinding or re-boring is the way to correct it.
How much allowance do you leave for honing?
Little, and the right amount depends on the form error after the previous operation, the material, the diameter and the honing process. Agree it with whoever hones: too little leaves form errors, too much costs honing time.