What's new
What's new

Speed for turning tubing

cuttergrinder

Hot Rolled
Joined
Mar 16, 2007
Location
Salem,Ohio
We have a job where they want us to turn some 8 5/8" dia mild steel tubing down to 8" with a .005 tolerance and a 63 finish. The wall thickness will be 1" when they are done. The tubes are 13' 8 " long. I'm thinking we could run the spindle in the cnc lathe about 150 rpm. What do you guys think.
 
Thats about 300 FPM so that should work with carbide tool. Bigger issue is going to be vibration.

Had some 6061 tubes I had to make into rollers for a printing press, aspect ratio longer then the OP's

Put them in the lathe, 1st pass was a roughing pass, with whatever tool was in the toolpost. H*** S*** finish was bad, vibration was so bad the finish was highly scalloped, strangely it didn't make any of the usual noises when it was running.

second pass, brand new TPGT, didn't really get better, as soon as the TPGT got to the section that was bad, same result.

1st thought was to get within .005 and get the tubes centerless ground.

But didn't have time, and as a last resort tried a 60deg threading tool, voila success. turned right thru the middle where it had been vibrating, evidently it didn't excite the tube to vibrate. It's feed rate sensitive though,too fast a feedrate will get the tube to vibrate, but nowhere as bad as the two previous inserts. I had to run at a low feedrate to get a decent finish that I finished off with 320 then 600 grit paper.

Lathe is Graziano SAG14.

I have some 20" long 22LR barrel blanks that I have to turn down from 1.25" to .920" in the near future, so that's the plan now, last few passes with the 60deg turning tool.
 
I have some 20" long 22LR barrel blanks that I have to turn down from 1.25" to .920" in the near future, so that's the plan now, last few passes with the 60deg turning tool.
I bought a machine off of a guy that did a lot of gun work. He used a negative rake insert tool in an aloris tool holder to turn gun barrels and he would adjust the tool up maybe only a few thousands at a time until the gun barrel would stop chattering. You have to get just the right height. Too high and it wont cut and too low and it will chatter.
 
The whole thing or just the ends?

If just the ends it could be easier to do it on a HBM if you have the tooling.
 
I've made plugs before and filled the tube partially with sand to damp out vibration. Nothing that big before though.

Could try taping some slabs of neoprene or rubber to the inside walls of the tube.

Be careful though, I've had rolled tube bow like a mofo after skimming the OD and the stresses take over.
 
That's why I was wondering how fast we can run the spindle. I figured up at 150 rpm, a finish cut at .007 feed will take a little over 2 1/2 hours. We may be abke to run faster but not sure until we get them in there.
 
Depending on the consistency of the material ID and the concentricity requirements; an arbor has worked really well for me for longer tubing.
 








 
Back
Top