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Using a die to cut a thread on brass/copper pipe.

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Brian John06/05/2014 06:06:36
1455 forum posts
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I have posted many questions on taps (quality and how to use them) but I have never asked about dies. I thought they would be simple to use ! I have some 3/16'' copper and brass tubing and I need to put a 3/16-40 thread on them ; they are to be used for live steam plumbing on a stationary steam engine.

I put the tubing in a small vice ; the tubing was wrapped in leather so as not to mark it. But I cannot get the die to cut. I am cutting from the side with the stamp ''3/16-40''. The other problem I am having is keeping the tubing from moving; I do not think the leather provides enough grip. I have ordered a larger vice with horizontal and vertical V notches to better hold the pipe but it has not arrived yet.

The dies are CS and purchased from Tracy Tools. The die holder just arrived today. It was purchased from ebay (''Faithful'' brand). There are some photos here. Have I got it set up correctly ?

dscn0006.jpgdscn0004.jpg

 

 

Edited By Brian John on 06/05/2014 06:23:52

Michael Gilligan06/05/2014 07:10:44
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Brian,

Try rotating that die so that the middle screw engages the split.

Loosen the two outer screws and tighten the middle one, to spread the die open a little ... Don't over-do this, or you could break the die [it depends how accurately the die and the holder are made] ... then tighten the two outer screws and proceed. ___ If the resulting thread is slightly over-size, loosen the middle screw and re-tighten the outer ones, then go over it again.

It's also worth lubricating the work with Rocol RTD "tapping compound" ... Copper is can sometimes be nasty stuff to thread.

MichaelG.

 

Edited By Michael Gilligan on 06/05/2014 07:11:33

Edited By Michael Gilligan on 06/05/2014 07:22:54

Edit: Revised my closing remark, in deference to Jason B.

Edited By Michael Gilligan on 06/05/2014 07:31:53

Brian John06/05/2014 07:19:14
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Okay, I will try repositioning the die so that the middle screw is in the split. Why is copper nasty stuff to thread ? I thought it would be easy as it is soft.

JasonB06/05/2014 07:24:23
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You also need to have reasonably thick wall tube, something like the KS range brass tube is too thin but the stuff sold by the ME suppliers should be OK if the right gauge.

I don't find copper tube too hard to thread, its more of an issue to tap.

Also worth pointing out that dies have a lead taper much like a taper tap so make sure you use the right side, its usually the one with teh writing on it.

 

J

Edited By JasonB on 06/05/2014 07:41:16

Bob Brown 106/05/2014 07:26:18
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If you need to hold small tube or bar in a vice, I drill a suitable hole in a piece of bar, run a hacksaw down one side so that it is half cut, slide in the tube and clamp the assembly in the vice.

Michael Gilligan06/05/2014 07:27:34
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Posted by Brian John on 06/05/2014 07:19:14:

Okay, I will try repositioning the die so that the middle screw is in the split. Why is copper nasty stuff to thread ? I thought it would be easy as it is soft.

.

Because it's soft, it tends to smear instead of cutting cleanly

... Contrast this with " Hard leaded engraving Brass" which we use for cutting clock wheels, this produces clean little chips.

MichaelG.

mick H06/05/2014 07:53:37
726 forum posts
21 photos

Brian, you might like to try turning up a piece of brass or steel which is a push fit in your tube. This will support your tube where it is held in the vice as well as where you are cutting the thread.

Mick

HomeUse06/05/2014 08:02:57
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A tip for threading/drilling copper - use full cream milk or single cream for lubrication - commonly used in past times. Make sure all residue is washed away as the acid in milk (lactic) will damage metals (and cement based items)

Edited By HomeUse on 06/05/2014 08:04:43

David Jupp06/05/2014 08:07:29
751 forum posts
17 photos

A chamfer on the end of the pipe can make starting the threading easier too.

Brian John06/05/2014 09:51:30
1455 forum posts
579 photos

I will try some of these ideas tomorrow because I have to go to work tonight. I am cutting from the side with the printing so i think I got that right but all I am doing is cutting a chamfer on the tube...not a thread.

I cannot turn anything in my new lathe yet as it is still in the box on the floor. I have to build a workbench for it first.

Michael Gilligan06/05/2014 10:21:59
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Brian,

This seems a very strong indication that the Die is adjusted much too small [which is quite likely, the way you have it installed] ... either that, or the tube is over-size !

With everything set correctly, I would expect to be able to thread 3/16" 40 tpi comfortably, without the job slipping ...

MichaelG.

JasonB06/05/2014 16:26:50
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Also worth checking that its 3/16x40 ME that you want as the PM Research engines may have MPT ( model pipe taper) thread or even their universal that is supposed to fit ME needs the fittings retapping

Brian John06/05/2014 22:18:27
1455 forum posts
579 photos

Yes, I know that PM Research engine have MTP on their steam inlets and outlets on the engine but I will be using straight pipe everywhere. I think that MTP is more trouble than it is worth.

Nobby06/05/2014 22:53:19
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Hi
Why not thread it in a lathe with pressure / support from tailstock this will keep it nice and square . and help it start
They  may be a bend in the tube so may not be able to do this .  Or if its a long peice you may need a small hole in the workshop wall ?
Nobby

Edited By Nobby on 06/05/2014 22:57:04

thomas oliver 206/05/2014 23:37:44
104 forum posts

I have recently had precisely the same problem with a die of the the same make from the same firm.. On examining the die with an eyeglass I could see that no relief behind the teeth had been ground in, and none of the usual fixes would solve the situation. Rather than waste time returning the die, I ground in the relief with a Dremel tool and a conical burr, when the die cut perfectly. I have had dies stamped CS fro Tracy in the past which were not hardened and tempered, and lost their edges immediately. In fairness to Tracy Tools, they never quible and exchange the goods.

julian atkins06/05/2014 23:50:39
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the use of threaded copper tube seems to be a bit of an oddity, and a peculiarity of some stuart turner designs. in miniature loco work it is virtually unheard of and we use silver soldered nipples on the pipe with unions and male connectors.

however ive done it a few times and i would never attempt small diameter stuff other than in the lathe with a tailstock die holder plus a number drill pushed hard into the copper tube so same can be put in the 3-jaw and clamped up.

i have very many ME size dies from tracy tools and never found them anything other than very good.

copper is a pig to thread. it tears easily if not very careful, regardless of what condition the die is or the tapping compound used.

cheers,

julian

Edited By julian atkins on 07/05/2014 00:17:09

Brian John07/05/2014 06:13:47
1455 forum posts
579 photos

Nobby : my lathe is still sitting in its box on the floor. It is not set up yet. Anyway, I should know how to use dies by hand.

There is a chamfer on the printed side and I am using that. I have tried again this afternoon after changing the position of the die so that the middle screw is on the split but with no success. The copper tube is just a mess ! I managed to cut a few threads on the brass tube but after that that the tube kept turning. I will have to wait for the larger vice with the V notches so that I can get a good grip on the tube.

 

Edited By Brian John on 07/05/2014 06:14:36

JasonB07/05/2014 07:25:00
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Julian, this is an American engine and they use straight pipe and threaded fittings a great deal both on steam and gas engines where nuts and nipples would be out of place. This is the sort of thing that I made a while ago.

Brian John07/05/2014 10:30:08
1455 forum posts
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I love the pipe work Jason. But what is it ? smiley How did you cut the threads on the copper tubing ?

Edited By Brian John on 07/05/2014 10:30:42

JasonB07/05/2014 18:00:39
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All the straight bits of brass & copper tube were done with it held in the 3-jaw chuck in the lathe and a tailstock dieholder cut under power at about 50rpm.

The bent ones were threaded after bending and held in a vice with flat aluminium softjaws using a diestock just like yours

In both cases I did not add internal support, just cut the thread.

The run on the left is the fuel return from the constany level carb and is 1/8" dia, threaded 5BA. The middle one is the fuel feed and brass fuel pump which is 3/32" dia and threaded 7BA. The ones in the background comming from the cylinder jacket to the brass water pump are the cooling pipes and they are 3/16" dai, threaded 3/16x40ME. Exhaust thats in teh photo below is 5/16" steel threaded 5/16x40ME

As for what it is, its a 1/5th scale model of a IHC (International Harvester Co) vetrical screen cooled hit & miss engine. This is it all together with teh cooling screen & tank and a video of it running minus tank.

J

Edited By JasonB on 07/05/2014 18:03:37

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