How would you do it?

[dnellans]

Long, soft metal pipe I’d like to turn down for a misc project.

ID consistency doesn’t matter but OD does. 24 finish length.

The ID of the pipe is larger than any live center I’ve got, so my tailstock support option is a steady rest. Dialed in after turning a small section of it through the headstock.

But the thin walled pipe is like a wet noodle and I can’t take even a 1 thou pass without it chattering in the middle.

How would you do it? I’ve got a steady, follow, and tailstock avail, but no live chuck for the tailstock.

 

[Dusty Stevens]

Id get a bullnose live center and id only turn a foot or so from the chuck. Once you get each one foot section turned then polish it. Chatter is a real bitch on a setup like you got there

 

[jackieschmidt]

Machine a slug with a small shoulder, tap it in the end, then center with a center drill just as if it were solid.

 

[tac284]

Curious what the ID is? You could try tube deadner, same idea they use in drivelines. I’ve seen guys use balled up surgical tubing shoved inside to. I’d machine a plug for the end with a smaller center drill, then use whatever center you have.

Things with the right ID I’ve used wood dowels.

 

[pdhntr]

....I’ve got a.... follow, .....

I am assuming that means you have a follower attachment for your lathe. It is my understanding the purpose of the follower is to follow along with the cutter and reduce or eliminate the chatter.

The plug in the end of the tube has been covered by others.

Jim

 

[boltfluter]

Slow down the rpm and speed up the feed rate for starters. On something that long it will push away in the center. As Dusty said, you make be stuck doing a section at a time and blending. Good luck!

Paul

 

[DaveTooley]

What Paul and Dusty said.

 

[ridgeway]

Follower and a smallest radius insert radius you have. 64th or smaller. Maybe stuff the inside with water pipe insulation? Trial and error...

 

[Tucker65]

You could try making plugs that tap into the ends. Filling the tube with sand might help with the chatter. Drill center in capped end for the tail stock. With it chucked up and you steady rest between the carriage and the chuck turn a spot to run the tail stock on some distance away from the chuck that doesn't chatter. Now move the steady rest to that turned spot to support the tube. Turn another spot farther down the tube and repeat this process until you have enough spots to work your steady rest down the length of the tube to turn the OD to you desired size.

-John

 

[hogpatrol]

Like Chuck posted, small radius tool bit, positive rake, right on center and run it as fast as it will go and .005 feed rate. Whatever RPM you're running is probably too slow of a surface speed. Also how are the headstock bearings? Any slop there and it's chatter city.

 

[JMA]

I have filled long tubes [6' 2.5 dia] with lead shot to dampen chatter worked real good.

 

[tobnpr]

What Dusty said. Bullnose live center, I wouldn't do it without given your OD is critical.

A bullnose live center, with the steady at the mid-point. Turn half of it, flip it around, turn the other half.
Blend with a file.

How much bed wear/tool drop?
Most lathe operations aren't significantly affected by bed wear, but turning between centers sure is- and it's exacerbated over long lengths. You didn't specify your +/- tolerance on the OD.

If you haven't done so, measure your tool drop.
Saddle up against the headstock as far as it'll go. Slide the tailstock up to it, affix a dial indicator to it.
Stick the tip of the indicator on the front left corner of the carriage, zero it.
Slide the saddle down the bed, observe the indicator. On older machines or those with a lot of use, variation can be significant, if so "map" it at varying distances from the headstock.

Copied this from the PM forum:
radius error = {.010/sin[tan-1(.010/R)]} - R
where R = workpiece radius

 

[therifler]

Machine a slug with a small shoulder, tap it in the end, then center with a center drill just as if it were solid.

right on jackie with the plug .also looks like a weld inside you'll want to grind that off if there is .

 

[scasa]

I'd get rid of the carbide and use a sharp HSS tool bit ground for this cut, minimum radius but sharp slow feed and light cuts I can never get a decent cut with carbide cause it takes too much push to make them cut

 

[hogpatrol]

I'd get rid of the carbide and use a sharp HSS tool bit ground for this cut, minimum radius but sharp slow feed and light cuts I can never get a decent cut with carbide cause it takes too much push to make them cut

This is another good option. The rake on insert tool bits is generally made for CNC equipment running high surface speeds. I've used brazed bits I ground myself with success on jobs like this. It is a fine line to travel though.

 

[Toolbreaker]

Plug the headstock end, fill with wet sand (or just about anything dense) to suppress harmonics, then plug & center drill the tail stock end like Jackie said. Your follow rest may help with keeping a belly out of the center section between the head and tail stock. .015" radius insert & start out at ~.006"-.008" feed/rev. Try about 70% of normal rpms and adjust from there. As mentioned, sharp high-rake HSS is very useful here also if it still wants to act up.

 

[dnellans]

Thanks for all the suggestions guys!

I've already slowed it down as far as I think it can go without starting to get bad finish from the rpm. I'm using a super small radius, uncoated insert, just like shown actually. Taking barely anything off on a pass at slow RPM is an excercise in patience for sure.

I thought hard about tapping some plugs in and filling it with sand to give it more mass, but that is a bunch of effort that I'm not sure will end up improving the deflection in it significantly. AKA - it will just be a heavier wet noodle.

So before I do that here is what I'm going to try...

I'm going to turn and tap in a single plug for a live center, then I'll turn just a 12 inch section with the rest of the pipe through the head (thankfully OD is under spindle bore), then move workpiece outboard and support the middle with the steady and the end on the live center. I'll have to sneak up to the middle with the steady to not deflect it while adding support.

If I'm thinking about the operation right, once I move it out, I'll dial in the tail stock and the turned middle both before and after adding the steady to get the outboard piece running co-ax. If the chuck has runout, then so be it because thats what i'm now turning to match the section that is beyond the steady. Even with the chatter, the whole tube is at least "close" in terms of diam, so it shouldn't be horrible I hope.

Of course, I've already missed my O.D. fucking with this piece, so once I figure out the right process - I get to do it all over again

 

[Walt Krafft]

What od, id, length, and material do you want to finish with?

 

[JMA]

Filling with sand or lead shot will not improve the delflection what it does is dampen the chatter.

 

[dnellans]

Filling with sand or lead shot will not improve the delflection what it does is dampen the chatter.

The chatter is a function of the piece whipping around though. If it was stiff enough to not have significant deflection, it wouldn’t be chattering? Those are related in my mind - am I thinking about it wrong?