View Full Version : Knurling stainless tube

02-19-2005, 07:37 AM
How do you knurl one and a quarter inch stainless steel tubeing with about a .120 wall thickness. I suspect that the tubing would distort badly from knurl tool pressure. It is tube with a welded seam on the inside and not drawn over mandrel material(DOM)

02-19-2005, 07:45 AM
Make a plug similar to an expanding mandrel with a groove to permit clearance for the weld.

The tapered expander can be drawn in with a screw if the knurl is some distance down, and a long screw with handle used to install & remove.

[This message has been edited by JCHannum (edited 02-19-2005).]

02-19-2005, 09:05 AM
If that is 304? it sounds like the stuff I used to resleeve Amal carbs. It was the only size I could find that fit after I machined it.

If it is 304 you are in for an adventure. You will have to support that mandrel at both ends and I would try to remove that seam. Even though the seam is on the inside, the one you see on the outside is as hard as a rock. I used HSS with a very sharp point to get down past it. Even then sometimes I had to change bits or resharpen.

Again if that is 304 it work hardens like mad and your going to need some quality knurls to make it look like something.

I would look for another material maybe?

Of course I can't keep trak of those numbers,303 304? One machines easy one doesn't. The tubing I used, work hardened like crazy and it sounds like what you have.


02-19-2005, 09:14 AM
If your tubing will be reasonably short, any chance you could knurl a solid piece of stainless and then bore it out?

02-19-2005, 09:50 AM
Type 302HQ is your best choice for cold forging, essentially what you're doing with the knurl. Lowest workhardening rate of the 300 series.

Type 303 gives you good machinability & welds well.

Type 304 is the most common. As Gene said, you're really gonna have fun (AGONY???) if you knurl 304.

Barry Milton

02-19-2005, 10:01 AM
Its 304 and I have a whole bunch to do for a friend who is building exercise equipment. Maybe a mild steel and chrome plated would be the ticket.

02-19-2005, 10:14 AM
Madman, that's probably how the "big boys" would do it in a production setting.

02-19-2005, 02:08 PM
Buy it already made.
There is a company called Ridgidized metals, in Buffalo, that specialises in textured stainless steel- they make all kinds of textures, including some that look knurled, in stainless. Not sure if they go all the way up 1/8"- but you could check. I bought some 16ga tube from Mcmaster Carr that actually was made by rigidised- Mcmaster only stocks one type, where rigidised will make you whatever you want. With a minimum order, you could get some of their really wild patterns in a tube, and your stuff would look like nobody elses.

If you absolutely must knurl tube yourself, you might have to fill it with CERROMET- this is a low melting point alloy, that is much safer and easier to use than lead- it melts in a double boiler, and is reusuable again and again. Costs about 25 bucks a pound, but you could just keep using it with minimal loss, for quite a while.

Charlie Rose
02-19-2005, 07:22 PM
Worked for Uncle Sam building subs every thing you can think of was made of 304 stainless,lot of it was knurled. It must run true so a skim cut is called for you will need to play with the od size to get the pattern to track. One thing that made it easer to get a good knurl was to cut a shallow "v" thread where the knurl will be,this gives the metal some where to go,again you have to play around with TPI and depth but once you get it working it's easy to repeat. We always used the pinch type tools ,cost more but work sooo much better.

02-19-2005, 07:36 PM
You're right, Charlie, a pinch type or clamp type knurl will be way easier than the bump style.

02-20-2005, 01:10 PM
If that is 304?

Cut knurling works best on 304 - I have never been able to get a decent bump knurl on it. It does work harden quite bad...