EAST AI Hydraulic Manufacturer
Since 2006
Views: 0 Author: ALEX Publish Time: 2026-09-10 Origin: Site
Written by Alex, Production Engineer at EAST AI
Customers send us bore diameter, length, and tolerance almost every time. Roughness gets left off the drawing more often than any other callout on a honed tube spec — and it's usually the one detail that determines whether the seals in that cylinder last two years or five.
A honed tube isn't just a pipe with a tight ID tolerance. The honing process leaves a specific cross-hatch pattern on the bore surface, and the depth and consistency of that pattern — measured as Ra, the average roughness value — controls how well the bore holds a thin film of hydraulic oil against the seal lip during every stroke. Too smooth, and the surface can't hold enough oil film, so the seal runs dry and wears fast. Too rough, and the peaks in the surface abrade the seal lip directly.
Ra is the arithmetic average of the peaks and valleys along the honed surface, expressed in micrometers. It's a single number, but it doesn't tell you the whole story on its own — two bores with the same Ra value can have different peak sharpness (Rz) and different cross-hatch angles, and both of those affect seal behavior independently of the average number.
For standard hydraulic cylinder tube, we typically hold Ra 0.4-0.8μm on honed bores and a tighter Ra 0.1-0.4μm on skived and roller burnished (SRB) bores. The SRB process produces a more closed, plateau-like surface rather than the open cross-hatch of conventional honing, which is why it can hold a tighter roughness band while still retaining enough oil film structure.
The honing stones cut in a crossing pattern, typically somewhere between 30 and 60 degrees, and this angle determines how the oil film moves along the bore as the piston strokes. Too shallow an angle and the oil gets wiped off in one direction faster than it's replenished; too steep and the pattern doesn't retain oil well at all.
We set the cross-hatch angle based on stroke speed and duty cycle, not just the bore diameter. A slow-cycling press cylinder and a fast-reciprocating vibratory application don't want the same honing pattern even at an identical Ra value, because the oil film has less time to redistribute between strokes on the faster application.
Polyurethane seals and PTFE-based seals behave differently against the same bore finish. A bore that's well matched to a polyurethane seal can run a PU seal dry within a season if it's actually fitted with a harder PTFE seal package, because the two materials need different amounts of retained oil film to avoid stick-slip wear.
This is one of the first questions we ask when a customer sends us a seal brand or part number along with the bore spec — the seal compound changes what we'd otherwise recommend purely from the bore diameter and pressure rating.
One pattern we've run into more than once: a cylinder rebuilder reports that new seals wear out within a few months on a bore that "looks fine" visually and passes a basic gauge check on ID diameter. The tube measures within tolerance on diameter every time, but the roughness has drifted outside the original Ra band because the honing stones on the rebuild line were past their service interval.
Diameter tolerance and surface roughness are controlled by different variables in the honing process, so a tube can be dimensionally perfect and still have the wrong finish. Once we re-checked and corrected the roughness spec on the replacement tube, the seal wear complaint stopped recurring — the diameter had never been the issue.
We check surface roughness on every batch using a profilometer as part of our standard pre-shipment inspection, not just on request. The reading is taken at multiple points along the tube length, because roughness can drift along a long bore even when the average value at any single point looks acceptable.
The inspection record is kept against the production batch, so if a seal performance question comes up months after delivery, we can pull the actual roughness data for that specific tube rather than quoting a generic spec sheet range.
Send us your bore diameter, tolerance, stroke length, and cycle rate, along with the seal brand or material if you know it. If your own engineering spec already calls out a target Ra range or cross-hatch angle, tell us that directly and we'll manufacture to it.
What Ra value should a hydraulic cylinder honed tube have? Most standard hydraulic cylinder honed tube runs Ra 0.4-0.8μm, with skived and roller burnished (SRB) tube typically held tighter at Ra 0.1-0.4μm. The right value depends on seal type, stroke speed, and duty cycle rather than bore diameter alone.
Can a bore be too smooth for good seal life? Yes. A surface that's too smooth doesn't retain enough oil film at the seal lip, which can cause the seal to run dry and wear prematurely — the same failure mode people usually associate with a bore that's too rough.
Does surface roughness affect welded cylinder assemblies differently? Roughness itself is a bore-finish property independent of how the tube is joined to the end caps, but on welded assemblies we do recommend re-checking the bore near the weld zone, since heat input can occasionally affect the surface locally.
How is roughness verified before a tube ships? We measure Ra with a profilometer at multiple points along the tube as part of 100% pre-shipment inspection, and the reading is recorded against the production batch for traceability.
Internal resources:
· Hydraulic Cylinder Product Range
External references:
· ISO 4287:1997, Geometrical Product Specifications (GPS) — Surface Texture: Profile Method, the standard defining Ra and related roughness parameters referenced in this article: iso.org
· ISO 9001:2015, Quality Management Systems — Requirements, referenced for our batch-inspection process: iso.org
If you're specifying honed tube and you're not sure which roughness band fits your application, don't copy a number off a similar-looking project. Tell us your stroke speed, duty cycle, and seal material, and we'll recommend a finish based on how the bore will actually run — not just what looks standard on paper.
