Tips For Dialing In And Indicating Tube With Steady Rest?

JimDawson said:
I think @Tozguy has the right idea here. Trying the thread a tube that is slightly out of round in a steady rest is not going to go well.

As it is the threads are not going to be a consistent depth or form. Holding this in a steady rest will make the problem worse.
Click to expand...
I think the ovalling was created by the plug being about .002" undersized. My guess at the moment is that there was a burr on the tube from when the supplier cut it and I didn't remove it before testing for a slip fit. Then when I tightened the jaws, 2 sides bowed in .002" and two bowed out .002" creating the .004 .000 .004 .000 readings I was getting. I am going to clean out the burr (if there is on one of course) and turn a new plug and see if that makes a difference. I don't think I mentioned but I was able to force it to about .001" using the steady but it seemed to be a very strained fit and I was to tired/frustrated to continue so I called it a day.
 
Hi shooter,

I'd also start at the beginning. Depending on the tube wall thickness, material, how it was manufactured, and how it is cut you may be starting off on the wrong foot.
  • is the tubing manufactured by folding and welding? if so it may have a seam on the inside diameter that interferes with the plug you made
  • are you crushing the tube in a vise when cutting it, making it out of round before even getting to the lathe?
  • are you making it out of round with the cut alone? thin walled tube can easily be forced out of round with the force of a bandsaw or other blade. Also, they can throw up burrs on the edges that need to be dressed.
Try to eliminate any of those problems first.

Is there any way that you can mount your 3-jaw chuck in the tail-stock to help you align that end while you get the stead-rest roughly aligned? If so, you could:
  1. use the 4-jaw chuck in the head-stock grab one end of the stock holding but loosely,
  2. use the 3-jaw chuck in the tail-stock grab the other end of the stock again loosely,
  3. place the fixed steady where it needs to be again loosely,
  4. remove the 3-jaw tail-stock support
  5. dial in the tube at the steady rest as best you can, tighten without distorting the tube
  6. dial in the tube at the 4-jaw/head-stock, tighten without distorting the tube
  7. double check the centering at both ends
All the above is done without the lathe running, turn by hand to see the indicators move.
Temporary plugs may be required if the tube is so thin that the chucks or steady alone change it's shape.

Good Luck, and please let us know how it goes! (what worked, and what didn't)

-brino
 
brino said:
Hi shooter,

I'd also start at the beginning. Depending on the tube wall thickness, material, how it was manufactured, and how it is cut you may be starting off on the wrong foot.
  • is the tubing manufactured by folding and welding? if so it may have a seam on the inside diameter that interferes with the plug you made
  • are you crushing the tube in a vise when cutting it, making it out of round before even getting to the lathe?
  • are you making it out of round with the cut alone? thin walled tube can easily be forced out of round with the force of a bandsaw or other blade. Also, they can throw up burrs on the edges that need to be dressed.
Try to eliminate any of those problems first.

Is there any way that you can mount your 3-jaw chuck in the tail-stock to help you align that end while you get the stead-rest roughly aligned? If so, you could:
  1. use the 4-jaw chuck in the head-stock grab one end of the stock holding but loosely,
  2. use the 3-jaw chuck in the tail-stock grab the other end of the stock again loosely,
  3. place the fixed steady where it needs to be again loosely,
  4. remove the 3-jaw tail-stock support
  5. dial in the tube at the steady rest as best you can, tighten without distorting the tube
  6. dial in the tube at the 4-jaw/head-stock, tighten without distorting the tube
  7. double check the centering at both ends
All the above is done without the lathe running, turn by hand to see the indicators move.
Temporary plugs may be required if the tube is so thin that the chucks or steady alone change it's shape.

Good Luck, and please let us know how it goes! (what worked, and what didn't)

-brino
Click to expand...
The tube is 316 stainless DOM (supposed to be seamless they tell me) 1.5" OD with .065" walls. Its for a rifle suppressor so concentricity is pretty important.

I havent cut it myself at all. It was ordered from online metals at 12". I cant say how they cut it. I would assume band saw but I really dont know. I planned to use a razor sharp cut off tool to avoid bending it when I cut it from 12" to 7.8.

I really dont have a way to mount the 3 jaw in the tail stock. Its a 5" chuck and the tailstock is MT2 taper.

Is setting the steady rest before setting the chuck standard? If I went with the 3 jaw instead of the 4, would the pressure be more evenly distributed and cause less distortion?
 
shooter123456 said:
Its 1.5" OD 316 seamless with .065" walls for 1.37" ID. I have to thread the inside so I could only plug one end. I suppose I could do both to get it running true then set the steady rest. It would be tough to remove the plug though wouldn't it?
Click to expand...

Cutting good threads inside that pipe under these conditions is a considerable challenge. Knowing what the part is intended for, and taking inspiration from motorcycle mufflers, could a sleeve be made that is threaded inside and then permanently fixed in the end of the pipe?
 
shooter123456 said:
The tube is 316 stainless DOM (supposed to be seamless they tell me) 1.5" OD with .065" walls. Its for a rifle suppressor so concentricity is pretty important.

Is setting the steady rest before setting the chuck standard? If I went with the 3 jaw instead of the 4, would the pressure be more evenly distributed and cause less distortion?
Click to expand...

No, it would be worse. A six jaw chuck would be better than the 4 jaw for thin pipe. But that is $$$$.
 
Tozguy said:
No, it would be worse. A six jaw chuck would be better than the 4 jaw for thin pipe. But that is $$$$.
Click to expand...
I would like to get a 6 jaw, but as you said, $$$$. There is never enough going around to do everything I want to do...
 
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