Tips For Dialing In And Indicating Tube With Steady Rest?

[shooter123456]

I need to thread a 1.5" 316 seamless tube on my PM 1030v lathe. I have done this kind of thing in the past with a HF 7x12 lathe but it was kind of a hack job and I wan't more precision now.

I turned down a plug to put in the tube until it was a very tight fit. Then I stuck it in the 4 jaw and tried to indicate it as true as I could at the spindle. I was able to get it to about .004" and then I was getting two peaks and two lows. As in jaw 1 was 0.00", jaw 2 was .004", jaw 3 was .000" and jaw 4 was .004 again. That made me think it was ovalled out. Am I expecting too much from the tube? Should I turn down a slightly larger plug and use a mallet to force it in? Is there a way to tell if the tube is no good? The first tube was no good, I think from my cut off saw. It was bent all over the place.

Once I get it dialed in at the spindle, whats the best way to get it dialed in straight? When I got it dialed to .004" it was off by about .030" at 12" out. Is there a way to dial it in at the steady while keeping it straight?

 

[WesPete66]

I hardly have any answers, but maybe have some thoughts to consider..
As to the condition of the tube, if you were to put it on a v-block and turn it under a dial indicator you would get an idea of how round the part itself is. If it then ovals out in the chuck, then you know where the trouble lies.
I had the same question about the steady rest. What I found is that you mount the test indicator onto the face of the chuck with the point resting on the far end of the part near the steady. Then as you turn the chuck/part the indicator reading tells you which way to adjust the steady rest rollers. (I have yet to gather the test indicator and holder to allow me to try this..) I did find some good youtube vids showing this.

 

[Tony Wells]

If it's not too rigid (read: too tight in the chuck) just knock it around with your palm out where the rest is going to run. Or another way is to pick a spot somewhere close to the chuck where it can be made run true, and slide the steady rest to that point and adjust the rest there, then move it out where you want to run it. Generally there isn't enough wear on the bed to cause alignment issues for this. Yet another way is to make or get a live center for the tailstock and after indicating at the chuck, adjust the steady rest with the tailstock in the tube.

Edit to add: You can't use the tailstock to help if you have only a sawed tube. It should be machined flat and square. That said, of course you need the steady to face it square. It's a catch 22. You can probably get it close enough just bumping it around to face it, then go to the center/tailstock to get the steady right on. The problem is that if the steady is not adjusted to run on the spindle centerline, the work WILL walk out while rotating. But a quick facing cut won't take long, and the walking out won't happen all at once. Just don't start the lathe and walk off. Start it, get it cut, and stop it.

I would add though, that 0.008 out of round is not going to run well in your steady rest. And vee blocks can be misleading, because they are providing 2 points of contact @45° while your indicator is running on one. Some of the egg won't show, depending on how many lobes there actually are. Same with a mic. It only shows the difference between 2 point measurements. Some out of round conditions won't show with that method either. Roundness can be a little tricky.

 

[Tozguy]

What Tony said.
What is the wall thickness of the pipe?
With a steady I'd be concerned about the pipe walking out of the 4 jaw. What about putting a plug in both ends and holding the pipe between centers?

 

[shooter123456]

I hardly have any answers, but maybe have some thoughts to consider..
As to the condition of the tube, if you were to put it on a v-block and turn it under a dial indicator you would get an idea of how round the part itself is. If it then ovals out in the chuck, then you know where the trouble lies.
I had the same question about the steady rest. What I found is that you mount the test indicator onto the face of the chuck with the point resting on the far end of the part near the steady. Then as you turn the chuck/part the indicator reading tells you which way to adjust the steady rest rollers. (I have yet to gather the test indicator and holder to allow me to try this..) I did find some good youtube vids showing this.

I will give it a try with V-blocks. I think it was only ovalled near the chuck and the fact that it was consistent makes me think it was bent by the chuck. Ill try a new plug then use a dial at the chuck and near the end and see what I can do.

 

[shooter123456]

If it's not too rigid (read: too tight in the chuck) just knock it around with your palm out where the rest is going to run. Or another way is to pick a spot somewhere close to the chuck where it can be made run true, and slide the steady rest to that point and adjust the rest there, then move it out where you want to run it. Generally there isn't enough wear on the bed to cause alignment issues for this. Yet another way is to make or get a live center for the tailstock and after indicating at the chuck, adjust the steady rest with the tailstock in the tube.

Edit to add: You can't use the tailstock to help if you have only a sawed tube. It should be machined flat and square. That said, of course you need the steady to face it square. It's a catch 22. You can probably get it close enough just bumping it around to face it, then go to the center/tailstock to get the steady right on. The problem is that if the steady is not adjusted to run on the spindle centerline, the work WILL walk out while rotating. But a quick facing cut won't take long, and the walking out won't happen all at once. Just don't start the lathe and walk off. Start it, get it cut, and stop it.

I would add though, that 0.008 out of round is not going to run well in your steady rest. And vee blocks can be misleading, because they are providing 2 points of contact @45° while your indicator is running on one. Some of the egg won't show, depending on how many lobes there actually are. Same with a mic. It only shows the difference between 2 point measurements. Some out of round conditions won't show with that method either. Roundness can be a little tricky.

There is a way to determine whether it is "Too rigid"? When I use the 4 jaw (only had a 4 jaw about a month now though) it tends to be incredibly tight with the loosen the lows and tighten the highs technique.

I could probably run a dial test indicator and a dial indicator (I have 1 of each but 2 of niether) near the chuck and near the end and see if I can get both of them steady. Maybe get the 4 jaw close, then loosen it and tap it with my hand? Would a 3 jaw be better in this case? My 3 jaw tends to do pretty well.

The more I think about it, I think my plug must have been undersized. If it was .002" undersized, which would make sense if there was a burr in the tube from when the supplier cut it off (I can't remember if I checked for one which makes me think I didn't), when I squeezed in, part would shrink to -.002" then the other two sides would swell to +.002" which would account for the .004 .000 .004 .000 reading. I didn't leave it in the chuck and I hope it won't stay that way. It was only chucked for 15 minutes tops.

 

[shooter123456]

What Tony said.
What is the wall thickness of the pipe?
With a steady I'd be concerned about the pipe walking out of the 4 jaw. What about putting a plug in both ends and holding the pipe between centers?

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?

 

[Wreck™Wreck]

Tubing is not round, the larger the less round it is. If you want to prepare it for a steady put something on the tailstock end, it doesn't have to be a plug nor fit in the ID, indicate it there and knock it around with a mallet until it is as close as possible then do the chuck end. Tighten and lock the TS quill and if permitted turn a band on the OD away from the threads wide enough for the steady rollers, on such a small DOM tube this may require only a few .001's, set the steady there and go to town.

If a band is not permitted use a Catshead. You will notice that nearly every hydraulic cylinder has a steady rest band near the open end. Running a part that is even slightly out of round in a steady will result in the same or more error on the turned diameter.

As a side note if you use a steady with roller bearings DO NOT let chips get between the rollers and work or Catshead. I broke the frame of a steady on a 20"+ lathe this way, the steady had to get bigger or the work smaller, the work won and the casting broke.

I do it this way

 

[shooter123456]

Tubing is not round, the larger the less round it is. If you want to prepare it for a steady put something on the tailstock end, it doesn't have to be a plug nor fit in the ID, indicate it there and knock it around with a mallet until it is as close as possible then do the chuck end. Tighten and lock the TS quill and if permitted turn a band on the OD away from the threads wide enough for the steady rollers, on such a small DOM tube this may require only a few .001's, set the steady there and go to town.

If a band is not permitted use a Catshead. You will notice that nearly every hydraulic cylinder has a steady rest band near the open end. Running a part that is even slightly out of round in a steady will result in the same or more error on the turned diameter.

As a side note if you use a steady with roller bearings DO NOT let chips get between the rollers and work or Catshead. I broke the frame of a steady on a 20"+ lathe this way, the steady had to get bigger or the work smaller, the work won and the casting broke.

I do it this way

I appreciate your response. There are a few parts I do not understand. First when you say "put something on the tailstock end and indicate it there". What are you suggesting I put on the tailstock end? Are you just saying to put it in the chuck, get the tail end turning true with a mallet, then get it turning concentric using the chuck? Also you say "Tighten and lock the TS quill" what would I be tightening it against?

Unfortunately, I can't turn a band on the tube for the steady rest. I can't make the tube any thinner than it already is. Regarding a catshead, would I have the chuck hold that or is the best bet to attach it to the tube then turn the catshead in the steady rest? I don't have one now so I would have to make it. Can you suggest a material for it?

I use a steady with bronze tips. I try to keep it pretty clean but is it as much of a concern as with the roller bearings?

Again I really appreciate you sharing the knowledge. I came here to learn and feel like I am getting exactly what I need.

 

[JimDawson]

What about putting a plug in both ends and holding the pipe between centers?

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.