Big problems putting thread into 1/4" copper pipe

[jamespetts]

I have been trying without success to use my 1/4" 32tpi die to put a thread into some 1/4" copper pipe properly. I can get it started, and even get a thread, but the die cuts far too deep, and the copper pipe becomes extremely weak at the thread. I have tightened the middle screw on the die stock as far as it will go (to the extent of slightly damaging the screw head and my thumb), and starting it first from one side of the die, then the other, but all to no avail: it still cuts so deep that I can see the thread ridges from inside the pipe.

Can anyone provide any assistance? I should be extremely grateful. (If it is of any help, I am using a die and die stock bought from Stuart Models).

[houstonceng]

The 32TPI die is probably cutting correctly and the depth of the thread will be 640/TPI in thousandths of an inch. So it'll be 20 thou deep. Have you tried lubrication on the die ? Copper is such that it tears rather than cuts and a bit of lube can help.

There are a few ways of getting a better thread :-
1. You may need thicker walled copper pipe.
2. You may need to use 40TPI or 60TPI screwing tackle to reduce the depth of cut.
3. You should really thread a brass extension and solder it onto the pipe.

Copper pipe is usually not threaded but soldered into a flange or nipple fitting made of brass.

Why are you trying to thread the copper pipe ?

[ron]

I agree with Andy you would be better avoiding threading copper pipe, if for whatever reason you have to, you will get better results using washing up liquid, neat, as a lubricant.
Ron

[jamespetts]

Thank you both very much for your replies :-) I did not know that it was inadvisable to thread copper pipe, largely because the machinist built Stuart Score that I bought over eBay had threaded copper pipe with it, and it will now be very difficult for me to redesign things so as not to have to thread copper pipe, or even to use a higher TPI.

I shall, however, try using washing-up liquid as a lubricant - will this, do you think, stop the thread from being cut too deep? How should I best apply it?

Thank you again for your help :-)

[ron]

Just put some neat washing up liquid on the die, with the die as wide open as you can, and put some on the pipe end and away you go.
Ron

[mutley]

might help to use thicker wall copper pipe and not hte usual thin walled stuff.

[circlip]

You could also "Neck" the end of the pipe down by making a reducing block.

[Shawki Shlemon]

I don't know what this pipe bore has to be ,if all you need is say 1/8" bore ,I suggest you turn a short piece of bronze 1/4" o/d and reduce one side to the bore of your pipe and drill it through 1/8" or less and silver solder it on to your pipe ,then tap the bronze end 1/4-32 ,no problem .

[jamespetts]

Thank you all for your help :-) I tried the washing-up liquid and it did make a difference. I can still see some scoring on the inside, but it doesn't seem so pronounced. It seems that part of my problem was trying to bend the pipe with the thread in place, which I don't think was ever going to work - bending 1/4" copper pipe to go around sharp corners is not easy at the best of times. I think that I just about have it right now, though: as good as it'll ever be, in any case (slightly kinked but serviceable).

[dickdastardly40]

James,

If you are bending the pipe and are getting kinking in the inside of the bend, you could try using a bending spring if one is available in 1/4" or perhaps annealing the pipe (if it not ready annealed) before you bend it

Just a thought, others may know better.

Al

[baggo]

Another method I've used with some success is to get a piece of suitable sized bar (I use aluminium) and machine a groove in it the same width as the diameter of the pipe and making the diameter of the bottom of the groove twice the radius of your bend. Use that as a former to make the bend. The sides of the groove prevent the pipe flattening out sideways when you bend it round. In theory the bottom of the groove should be rounded but I've found a square bottom groove made with a parting tool works ok.

John

[Shawki Shlemon]

Baggo I made one surprisingly from 1" aluminum and have a number of grooves from 1/32 to1/4 " over 20 years ago and still use it . I anneal the tubing and bend as required , it is not 100% but not far off .Cheap and useful .

[steam4ian]

G'day all

Is there any relationship between minimum radius, pipe diameter and wall thickness?

I have some bending springs I picked up at a modeler's shop but The spring limits the bend radius and then can be difficult to get off the pipe. Consider a siphon tube for a pressure gauge. I am interested to know what is the smallest bend you can make with a block

Regards
Ian

[baggo]

Hi Ian,

I've never come across any 'tables' for minimum radius for pipe bends but no doubt some do exist.

Most of my bending has been done with small diameter (less than 1/4") pipes for 2½" gauge locos so my experience is a bit limited. Using the groove in a bar method I have managed to put a 7/32" radius 'U' bend in 5/32" diameter thin wall tubing with no problem. You should be able to reduce the radius with smaller diameter pipe but will have to increase the radius for larger.
I think it is easier to bend the thicker wall tubing than the thin as it's less liable to kink.

John

[circlip]

Tables do exist for min. bending radius of industrial size pipes, but haven't seen them for toy sizes. the main thing to consider in our sizes is how tight we really need to bend? If you look at the pressure ratings given for steam pipes in our sizes, these are compromised by bending a tight radius cos you're stretching the wall on the outside of the bend, ie. thinning it.

[ron]

I've got quite a handy gadget that is designed for bending car brake pipes neatly without collapsing the pipe, it didn't cost much in the local auto shop years ago, it's only drawback is the minimum pipe size is 3/16" OD.
Ron