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OD and ID turning a large thin wall tube

swarf_rat

Titanium
Joined
Feb 24, 2004
Location
Napa, CA
I am about to make a new rudder bearing for the boat, this involves a SS sleeve that gets bonded to the carbon rudder post to act as a bearing race for the Delrin rollers in the bearing. The size is close to 6" sch40 pipe, so I can get 316 or 2205 relatively cheaply. This comes with nominal OD/ID of 6.625/6.063" and needs to be 166/160mm finished (6.535/6.299"). About 5" long. Tolerances are loose, maybe 0.005, but it needs to be round. The question is how to chuck it.

The pipe probably won't be round when I get it and I expect chucking it in a normal 3 or 4 jaw won't help keep it round, and may not hold it well enough. I have a 6 jaw I can resurrect but I don't think that is a solution either. Any suggestions on how to hold this?

My best ideas are to use some pie soft jaws that would let be grab maybe 2", bore (or turn) 2" at the end (which is furthest from any chuck caused distortion), swap ends and repeat a couple of times hoping to get a round hole. Then bore ID and OD in passes hoping it won't worm around too much as the material comes off. In this situation, better to grab OD or ID?

Also, how big/stiff a boring bar do I need to get 5" into 316 or 2205? 2205 is preferable as the part has problems with crevice corrosion. I've never turned 2205, it is supposed to be tougher than 316.
 
If it were me, I would use pie jaws gripping on OD and start with 5.25 hanging out of chuck. Bore ID with 1.25 bar then rubber inside while turning OD. Part 20-30 long, flip and face. Could turn section of OD round and put a steady rest in then put center in while turning OD. Have to do it and see how much ringing you get. I have some upsharp inserts that cut really free and get me by when a DNMG sound tingy.
 
I'd rough the blank to remove any possible stress, then finish the bore and O.A.L.
Then turn a plug that just slips into the ID so you can chuck the OD without distorting it. Turn half, flip, done.
 
Once it is round, I can turn a plug to fit and keep it round, but how to get it round to start with? I might get lucky and the piece they sell me will be pretty round, but that's not been my experience with pipe. Even clamped in machined-to-diameter pie jaws, if it isn't round it will be distorted, and spring back when unclamped. If I could get the ID round and finished, I could turn a plug for each end and put a center in the tailstock.

Is the rubber inside to dampen ringing? Unfamiliar with "upsharp inserts" - can you point me at some?
 
How come you care about the o.d. ? If it's just going to get bonded into the hull to act as the outside race, no point in worrying about it.
In the OP it's stated that this sleeve is bonded to the rudder post, not the hull. so serving as the inner race for the bearing.

Sounds like a pretty fancy boat to have a carbon rudder post and Delrin roller bearings. Best I've ever had was a stainless post and a bronze bush in the hull with a stuffing box to keep out some of the water. Worst I've had was an outboard rudder with stainless on stainless gudgeon and pintle. Nearly lost that one once.
 
I did think about welding it to a plate. I worry about distorting it from the welding. did you find that to be a problem? I'd probably do a bunch of small tacks first then a full pass and hope that when it was cut off, it didn't spring to a different shape.

Yes the OD dimension and roundness are the most important. The id can be a little rough - it promotes adhesion - and a bit off dimension but not too far. There is no way to true the OD once installed on the rudderpost, experience has shown that it needs to be round within a few thousandths or you will feel it in the steering.
 
I did think about welding it to a plate. I worry about distorting it from the welding. did you find that to be a problem? I'd probably do a bunch of small tacks first then a full pass and hope that when it was cut off, it didn't spring to a different shape.
Some tag welds will do Like 20 to 30 % of a full pass With decent amount of filler material


Peter
 
I'd rough the blank to remove any possible stress, then finish the bore and O.A.L.
Then turn a plug that just slips into the ID so you can chuck the OD without distorting it. Turn half, flip, done.

I would recommend sumpthing along these lines.

Although I would likely start with a pc maybe 7" long.
Face and clean up bore 1" deep.
Tap, beat, or press a plug in.
Turn around and make your part, but as mentioned above - IF ROUNDNESS IS AN ISSUE - then sneak up to it from both ID and OD, but this will likely get that sucker singing quite a tune.

If you will be pressing this into something else in final assy that will force it round, then you wouldn't need to worry quite so much about stress relief, and then - given the numbers that you posted, I would want to clean the OD, and then come back and take the ID in one shot.

You would want to take a skim cut to qualify size, but then if you could take either all of it in one pass, or at least quite a bit of it, that would help to keep the ringing out of it - some anyhow....

Yeah, you have .300 to come out of the bore, so, 2 passes, but I would want the 2nd pass to be at least 1/2 of that, with a slow RPM and feed.


Maybe even just doo 1/3 of the bore depth at a time.
Finish 1", then start the next 1.5", then the last 2.5".
This would prolly be best.



On second thought, the only way to relieve the stress and re-chuck it w/o forcing somewhere other than where it wants to be, is to skim cut ID/OD and face it. Then I take rings like this and actually clamp them to the faceplate - as if they were on a mill. This is the only way that you are going to turn it after skim cut w/o your set-up forcing it back out.

Clamp from outside to bore, then clamp from inside, remove outside clamps, and then clean up OD.
This is a lot of work for one pc this small tho.



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Think Snow Eh!
Ox
 
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Send the blank out for stress relieving.

Then to a wire EDM shop.

No sweat. But you won't have all those billable hours with the turning methods.
 
Why not use an anodized aluminum sleeve? Perhaps Jefa has one in stock. I just serviced the rudder on the Medicine Man, and its Al sleeve wasn't bad after 20 years in the salt water.

If i were to make a sleeve i would start with a much thicker wall OD and bore it to the finish dia, then mount on mandrel and turn it down. A bit more waste but much more controlled.
 
I machine similar thin tube parts from pipe all the time, and in the same materials.

2205 & 316 don't need stress relieving.

Cut pipe >6" long.

Rough turn OD just enough to chuck it (you will be cutting this off later).

Pie jaw or 6-jaw chuck it on the newly finished OD.

Bore the ID first, bore it to size. This is your critical dimension, so you should do it first while there is the most meat on the part.

Use the biggest boring bar you have. If you have a anti-vibe bar, use that for finishing. Leave several passes worth for the anti-vibe bar, so that you can figure out your d.o.c. Dont expect anti-vibe bars to worth 1st shot.

If you dont have antivibe bar, use biggest boring bar and for finishing use smallest radius insert you have. make sure your d.o.c is a little larger than your tip radius. This will ensure that the insert is digging into the part and not being deflected. Hard to explain this with text, there's some pictures that describe the concept.

light cuts/spring passes on 2205 will just drag. You need to cut, not grind.

Dont unclamp part, put an old bicycle tire or some rubber pieces and a shop rag on the ID.
Turn down the OD. Take your time. hit it with sandpaper if you have to..

cut off the end. part it off if youre a tough guy, or just saw cut it and face later.
 








 
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