FRUSTRATED with threading tubing

[doublereefed]

I am trying to thread 3/16, 1/4, 5/16 tubing and it isn't going well. For instance, I need thread both ends of a 2" length of 1/4" tubing... I've tried copper and brass. How in the heck are you guys holding the pipe so you can thread it without marking/marring?

I have a Sherline lathe; the 3 jaw chuck isn't strong enough to hold brass tube, and it crushes/mars copper tube. I can do longer lengths sometimes well enough in a vise for the one end, the cut to length, thread into a fitting (like a 90 degree) in the vise, and then thread the other end.

There's got to be a trick, tool, clamp... something!

Thanks!

-Richard

[10KPete]

Collets. Make one to fit. 1/2" rod. Drill hole to fit tube. Slit one side with a hack saw. Joe's yer nephew!

Pete

[doublereefed]

Collets! ... seems I should have know that. I have a set, off I go. Thanks Pete.

[Carrdo]

Turn a piece of brass or hardwood dowel to be a nice light push fit to the inside diameter of the tube to prevent crushing or deforming the tube also if it is very thin walled.

[BillF]

One thing that I find helps a great deal is to use the Sherline to pre-cut a taper on the end to be threaded and then (with the headstock still offset) use the threading kit to cut threads to maybe half the final depth. Then I hold the tubing in a flaring-tool jig. Now the NTP/MTP die aligns easily and has minimal work to do to form the final thread profile. (Of course this is mostly for brass.)
- BillF

[FLtenwheeler]

Tim

I use a battery powered drill to thread my brass tubing. I use model taper pipe threads

Tim

[Fred_V]

Use a Moly heavy duty cutting oil. That really made a big difference for me. Copper is real sticky when threading. Use the screw to open the die for the first cut then close the die for a final cut.

[RET]

Hi Richard,

All the replies are well worth listening to and each one helps. Using them all together will make a big difference. Threading, especially with dies places a lot of force on the work. When you combine that with trying to hold tubing in a three or even a four jaw chuck, it's a recipe for failure. The combination of collets together with supporting the inside of the tube makes things a lot easier. I use collets a lot because they are accurate and fast.

The ME (model Engineer) threads, especially the 40 pitch series were developed specifically for threading tubing because the thread depth is minimal. If you are trying to thread with a taper pipe thread, it takes a lot more torque because the thread is coarse and deep and there also may not be enough material left at the root of the thread for mechanical strength. If you are worried about sealing against leaks when using a straight thread, pipe dope or the clear silicon sealant will work just fine. The silicone will also work just fine in the smoke box both for thread sealing and for sealing holes in the smoke box itself because it stands up to the temperatures encountered there. If you need to remove it, a knife works perfectly.

Richard Trounce.

[KarlKobel]

I had the most trouble making close nipples. Then I found a 'solution' almost by accident. I had to remove one from a fitting and used the split die as a clamp. I put the die in a 3 jaw chuck and the nipple came out easily. OK, its not really a solution, as I didn't want to abuse an expensive die as a clamping tool. The real solution was to make a threaded clamping fixture with three slots that the 3 jaw chuck can put pressure on the existing treads. For close nipples make sure the fixture bottoms out in the fixture.
Use the suggestions above for getting to that point.

Karl

[doublereefed]

All... thank you so much! Like a masters course on tube threading. I'm on it... will start building skills with all these techniques. My Sherline Mill has WW collets, can't hold the entire tube, apparently they are called "pug" collets. I found a cheap 5C collet holder, and a few 5C collets. That will at least give me a solid way to hold the tubing. I'm using brass where I need a curved pipe, and brass for straight runs. I'm using MTP dies. I will definitely try making a cut on the tube end for the taper, and also using the adjustment screw, cutting oil, and making a few passes to get the job done.

Again, thanks for putting me on the right path.

-Richard

[Bill Shields]

i thread short pipe by starting with solid round and drilling a hole through the center.

Close nipples are handled by:

1> thread one end of solid rod
2> cut to length
3> drill a 3/32 hole through
4> broach with a 1/8" hex broach (made from a 1/8" hex wrench
5 >hold 1/8" hex wrench in lathe, push on short pipe
6> thread the other end
7> drill out Id as needed.
8> heat then bend as needed

[Fred_V]

You can also hold the tube in a flare tool. It will distort the tube a tiny bit but it will hold really tight.