What's a Reasonable Minimum Wall Thickness for Parting Thin Stainless Tube on a Lathe?

There's no single number that holds across all diameters. As a working floor, parting a stainless tube wall much thinner than about 0.5 mm on a standard lathe setup gets unreliable fast. The diameter of the tube matters as much as the wall thickness itself. A thin wall on a small-diameter tube behaves very differently than the same wall on something larger.

Why stainless makes this harder than it sounds

Stainless work-hardens as you cut it, so the parting tool is fighting a material that gets tougher right at the surface it's trying to separate. Combine that with a thin wall that has almost no rigidity to resist the radial pressure of the blade, and the tube wants to deflect away from the tool instead of shearing cleanly.

Once it starts deflecting, the cut gets inconsistent. The tool can grab, and on a genuinely thin wall that grab can pull the part off center or snap the tube.

Geometry compounds it. A short, well-supported length behaves better than a long overhang, because the unsupported length acts like a spring under load. Parting near the end of a long thin tube held in a collet with a lot of stickout means fighting deflection before the tool is even fully engaged.

What actually helps

Support matters more than tool choice. A follower rest or a snug-fitting mandrel inside the tube reduces the ovalizing and deflection that thin-wall stock is prone to under radial cutting load.

A sharp, narrow parting insert with good chip clearance reduces the force needed to make the cut. On thin material that matters directly, since force is what causes the deflection in the first place.

Speed and feed also shift in the opposite direction from what feels intuitive. A slower, controlled feed with a sharp tool tends to hold up better on thin stainless than pushing feed to fight work hardening. Pushing harder generates more heat and more hardening right where you're trying to cut through it.

When to stop trying to part it on a lathe at all

If the wall keeps getting thinner than the tube can support under any reasonable setup, that's a signal the part might be better made a different way. A solid bar bored out instead of tube stock is one option. Accepting a slightly heavier wall than the ideal design calls for is another, if it keeps the process reliable.

Chasing an aggressively thin wall through parting alone, without rethinking the stock or the operation, usually costs more in scrapped parts than it saves in material.

Treat wall thickness and tube diameter together, not wall thickness alone. Support the tube physically wherever you can. Don't assume a sharper tool or a different feed rate fixes a problem that's actually about the part not having enough rigidity to survive the cut.