Honed Tube Surface Finish Explained: Ra, Cross-Hatch and Seal Life
The bore of a hydraulic cylinder is a bearing surface as well as a pressure boundary. Surface finish is what keeps an oil film between the seal and the steel, and it is the single most useful number on a honed tube specification.
What Ra actually measures
Ra is the arithmetic average roughness of the surface profile. Hydraulic honed tubes are typically supplied between Ra 0.2 and Ra 0.4 microns. Too rough and the seal lip abrades; too smooth and the surface cannot retain the oil film that the seal needs, which also causes early wear.
Why the cross-hatch pattern matters
Honing leaves a controlled cross-hatch of fine grooves, usually at 30° to 45° included angle. Those grooves act as micro-reservoirs that hold oil against the seal during stroking. A bore that has been skived and roller-burnished looks brighter but retains less oil, which is why honed tubes remain the preferred barrel material for high-cycle cylinders.
Tolerance, straightness and roundness
- Bore tolerance — H8 or H9 for general hydraulic service.
- Roundness and straightness — controlled so the piston does not bind over long strokes.
- Wall thickness — selected from working pressure with the required safety factor.
Frequently asked questions
What surface finish do your honed tubes carry?
Our honed tubes are produced to an H8/H9 bore with a typical surface finish in the Ra 0.2–0.4 micron range, verified with a profilometer before dispatch.
Can you supply honed tube cut to length?
Yes. Tubes are supplied in standard mill lengths or cut to your barrel length, with bore protection for transport.