Plateau Honing Explained: Why Bore Finish Isn’t Just About Ra

Two bores with the same Ra can seal completely differently. How plateau honing and Rk, Rpk, Rvk parameters really determine seal life.

The Counterintuitive Truth About Bore Finish: Why a "Smoother" Tube Can Actually Destroy Your Seals

An engineer once rejected a batch of honed tube because its Ra reading was slightly higher than the drawing specified. A week later, he called back, completely puzzled. A competitor’s tube with a lower Ra was giving him significantly worse seal life in his cylinders.

How can a rougher surface outperform a smoother one?

The answer exposes one of the most common and costly misunderstandings in hydraulic cylinder specification: Ra alone tells you nothing about how a surface will actually perform.

Ra is just an average. It treats a surface full of sharp, seal-shredding peaks the exact same as a surface with smooth, gentle plateaus, as long as the math works out. A lower Ra number can easily hide a surface profile that acts like a microscopic saw blade against your piston seals.

What the engineer was missing was the shape of the surface—and specifically, whether the tube had been plateau honed.

In our latest technical deep dive, EAST AI explains how plateau honing solves this paradox by engineering the bore surface for its actual job. You will discover:

Why a two-stage honing process creates the ideal sealing surface: smooth load-bearing plateaus to protect the seal, and deep valleys to retain a life-saving oil film.

Why Rpk, Rk, and Rvk (the material ratio parameters) are the only reliable way to specify a functional bore finish—and why Ra is practically useless on its own.

How matching the plateau surface to your specific seal type (from soft elastomers to hard PTFE) eliminates mysterious wear and intermittent leaks.

There is a specific set of functional parameters you should be writing on your drawings right now to guarantee seal reliability. If your current specification only lists an Ra value, you are leaving your cylinder's performance to chance.

Stop specifying an average and start specifying a function. Read the full article to learn how plateau honing can extend your seal life and design out wear failures.