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RE: [PSUBS-MAILIST] how to machine a big pipe end?



Problem solved!
 
Here's what I ended up doing. I'm fortunate to have a Harbor Freight store nearby, so as Dan suggested I went there and got a 20 ton jack ($39) to replace the 2 ton jack I'd been using before. Note for future reference... they carry 50 ton jacks! With that I was able fairly quickly to get the thing approximately round. But curiously the diameter ended up too large all the way around. Only by about 0.004" though, so I went at it with a hand file and emery paper. Once I got close, test fittings of the endcap marked the contact spots and told me where to file. The whole process took about 6 hours.
 
As always, thank you everyone for the suggestions.
 
 
Alec


From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org] On Behalf Of Daniel Lance
Sent: Friday, November 28, 2008 18:04
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] how to machine a big pipe end?

Alec,
Go to Harbour Freight and buy a bigger hydraulic jack. They have some on sale right now. Keep working with the jack method. With patience you should be able to get to within a few thousandths of and inch.  I had this problem with the 12" pipe caps.     If you cut , weld and remachine then reweld  you could end up right back to where you are now.
Dan Lance
 
 
----- Original Message -----
From: Smyth, Alec
To: personal_submersibles@psubs.org
Sent: 11/28/2008 5:53:02 PM
Subject: [PSUBS-MAILIST] how to machine a big pipe end?

I have a typical fabrication difficulty, and am wondering if anyone can recommend a tool or idea.
 
The ends of my battery pods that receive removable endcaps have a SS inside shoulder, and were buttered in SS. The shoulder and SS were then machined to a close tolerance to seal with a similar SS ring on the edge of the endcap. When this machining was done, the pod pipe was only about 18" long so that it would fit on the lathe. That short bit has now been welded to a much longer one, and I've also welded on external stiffeners, through-hulls, etc. None of the welding was less than 10" from the machined end, which I thought would prevent heat distortion. One of the pods came out fine, but with the other I was wrong, the pipe end is now an oval.
 
I've tried stretching the short diameter of the oval with a 2 ton hydralulic jack. That corrected it a bit, but I still have about 0.015" to go. This jack can't stretch the pipe any further, it's reached its limit. But in any case, that's such an inexact way of fixing the problem I don't think I could get it properly round to the final few thousandths this way. I think I need to re-machine this pipe-end in place, and obviously it isn't going to fit back on a lathe as is.
 
Ideas:
 
- Cut the pipe again to put the pipe end on the lathe, and re-weld.
- Make a jig that will center on the pipe ID and have a longitudinal shaft, with an adjustable arm mounted to it and a lathe cutting tool on the end of that. Yuck, a lot of work.
- Is there some specialized tool out there?
 
Any ideas are welcome! BTW the pipe is 12.75" OD.
 
 
thanks,

Alec
 
 

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