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View Full Version : Best way to open up a 7/8x14 tube?


andym79
08-19-2014, 05:48 PM
Hi guys, I have sourced some 7/8x14 threaded tubing; it has an ID of .698". What is the best way to open it up from .698 out to .705"?

Would the best bet be to chuck it up and drill it out to .705 or get a die grinder or some of abrasive tool in there?
country gent
08-19-2014, 05:51 PM
Depending on finish and hardness a decimil reamer might be just the ticket. Otherwise I would bore it very carefully and go slow. only .007 there to work with.
andym79
08-19-2014, 06:16 PM
One of these?

113982

I can only find one in .708" at the moment!
wmitty
08-19-2014, 06:20 PM
you might be able to lap it out with a lead lap and lapping compound
marvelshooter
08-19-2014, 07:12 PM
How long is it? If you have already chucked it in a lathe how concentric is the existing bore to the OD? It can't run out much or it won't clean up.
andym79
08-19-2014, 07:41 PM
Its pretty concentric at the moment. The finish doesn't have to be perfect just that size and parallel to the OD.
andym79
08-19-2014, 07:56 PM
you might be able to lap it out with a lead lap and lapping compound

It might be the go. I would need to start off with some very coarse abrasive!
dkf
08-19-2014, 09:37 PM
Hold it in a 5C collet in a lathe and bore the inside out with a boring bar. The collet will not hurt the threads and runnout will be minimal.
1johnlb
08-19-2014, 10:59 PM
Its only .007, wrap 220 grit around a 1/2 inch mandrel and turn slowly until you get to the size you need. Then finish honing it with 1000 grit or steel wool. Be careful and get a uniform fit in the tube before starting.
W.R.Buchanan
08-20-2014, 12:03 AM
dkf,,, provided the correct answer to this question.

Good luck.

Randy
Blanco
08-20-2014, 12:37 AM
Ball broaching.
I heard of it but never actually seen it. Basically you push bearing balls down the bore one at a time. Each ball is slightly larger than the last.
Just make sure your balls are well lubricated!
GP100man
08-20-2014, 08:04 AM
That^^^^ does`nt sound like alot of fun !! but then it mite ????

:kidding: :popcorn:
zuke
08-21-2014, 08:27 PM
I've polished up LEE dies from 287 to 317 with my small drill press. Start with 400 and when your with .001 go to 600
montana_charlie
08-21-2014, 08:57 PM
The minor diameter for the valley of a 7/8-14 thread is .7858".
If you enlarge the ID of the tube to .705", the wall thickness (at the valley) will be about .041" when rounded up to the nearest thousandth. That's thinner than 3/64th of an inch.

Is that wall thick enough to do whatever it is you want to use that tubing for?

CM