Posted: 1/10/2026 10:11:53 PM EDT
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Customer needs a 5" Schedule 120 304L stainless pipe turned to about 5.00 diameter (plus 0.025 is O.K.) The needed length is a 166--3/16" long from a provided 23' long piece. My first thought was to use the 16" x 126" Monarch lathe which has a follower rest, but the steady rest with the roller bearings is not large enough. With bronze bearings, the steady rest provides too much friction and would overheat if I tried that. The only viable option now is to use the LeBlond 32" Heavy Duty Sliding gap lathe which does not have a follower rest. After setting it up with the cut to oversize length (14'), and indicated in at the chuck with a bull nose center, I found that the pipe has a bend in the middle of about 0.400". The other thing that I found (after squaring the ends and putting it between centers) is that the bend is more of a curve on one half while the other half is fairly straight.  Run-out was mapped on paper.The first attempt at heat straightening seemed to have resulted in it making things worse, but it did not have time to completely return to ambient by the end of the work day on Friday. My biggest concern is that even if we are able to get the thing fairly straight, a 0.218 nominal wall is going to be rather thin to turn without a follower rest. Chatter will be difficult to control. Plus, I don't have flood coolant so heat is going to be a problem in terms of linear growth. I'll have to use both the tailstock center and the steady rest but I'm not sure how to keep the tailstock in consistent compression without it bending the work when it gets warm. Then there is the issue of stress relieving as it is turned. And, to make matters worse is that the customer is expecting this to be done soon---like Monday. Oh, and it the pipe was made in China so I expect crap in the material that will chip tooling. Does anyone have advice on best practices to accomplish this successfully? |
If I were a hedonist, I'd be a hermit.
You need a good airgun if you don't have one already.
You need a good airgun if you don't have one already.
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Obviously, I'd have to move the roller bearing steady rest in increments to support the hollow shaft as I go. (Clarifying the above post about a steady. I think he may have meant a steady coolant flow.) In addition, the gap between the chuck and bed is now at 48" The part will need to be flipped to finish. Being such a thin wall, after flipping I may need to make an internal spider to keep the tube from permanent distortion when chucked. The external spiders I've made are just too large to fit internally on this nominal 4.063" I.D. |
If I were a hedonist, I'd be a hermit.
You need a good airgun if you don't have one already.
You need a good airgun if you don't have one already.
| Late to this, you may have finished it by now. I've had success on long thinwall tubes with capping the ends and filling with coolant, even used sand in one. It helps to keep it cool and dampens vibration. Shorter pieces I've used cerrobend to fill then melt out after machining, that would take a ton on your part though so it wouldn't be practical. Stainless, especially the lower alloyed material you get in Chinese pipe, will crawl all over the place. I don't envy you with that project. |
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