How to cut a thread on small pipe fittings 1/2 inch in length ?

I often buy 10 or so small pipe fittings whenever I order something from PM Research : 3/16 X 40 x 1/2 inch long. They are very useful.

I have the correct HSS die and I have no trouble cutting threads on longer pieces (over 1 inch) but I have found cutting small ones 1/2 inch in length to be impossible as there is no way to grip the pipe in the vice. It is just too small. How do they do it ?

Um ? Loctite it to a rod, cut the thread and then break the bond with some heat maybe ?

regards Martin

That would work but I am sure it is not how PM Research cut their small pipe fittings. They must sell hundreds every week so there has to be a quicker way.

I'm probably not quite understanding your question Brian, as I'm not sure if you are asking how PM Research make 1/2" long fittings (and how you could make/thread your own?) or if you want to modify their existing fittings?

The golden rule of turning things (particularly when they are small) is to do as much as possible whilst the 'work' is still attached to the parent material e.g. before parting/cutting off. That's how I'm pretty sure PMR will be doing it.

If you already have a semi-finished part and it needs a 'second' operation, then you usually need some form of mandrel or screwed fixture to hold it.

Tubal Cain used a "master-slave" system - essentially a simple MT holder, with a number of 'slave' fixtures to mount the work on. So for something threaded 40tpi - there would be either be a female or male 40tpi slave that the work was screwed onto - the whole slave + work assembly then being mounted into the holder for the second operation work.

These days (with the availability of ER collet sets) it's quite easy to make a set of slaves to fit a common collet size you have (say 12mm) and for most work this will be quite accurate enough. The slave is of course machined in the collet you intend to use it in.

For working something like pipe (when it's already cut to length) - then you can either Loctite it (as Martin suggests) or perhaps soft solder it onto some rod the same ID as the pipe. If you are going to be soft soldering the part later, there is less need to clean it up afterwards. However if you intend hard soldering the part - then Loctite is the better option but will need some cleaning.

If I've completely missed the point of your question - then my apologies in advance!

Regards,

IanT

Just seen your second posting Brian - sorry takes me a while to type this stuff...

So - the simple answer is to do as much work before you part off as you can - makes life so much easier.

Also - as an after thought.

Anyone wanting to clean out short lengths of pipe (or holes) that have soft (ish) gunge in them - should try TeePee's (the small inter-dental brushes). I have a range of TeePee sizes to hand (yup - still got some teeth left too) and just occasionally they are very handy for "other uses"...but do throw them away afterwards (or the wife will worry)...

IanT

Here is a link with a photo and my apologies for not putting this up earlier :

**LINK**

Edited By Brian John on 09/07/2015 14:27:45

You will need a tap as well but make with outer most thread done in the lathe and the o/d's turned. Part off to length. Screw into a fixture and run the die down the other end.

In this case I would be inclined to split the fixture and clamp it tight with hex screw otherwise you might have problems getting it out again. If you can't split things have a thread running right through the fixture and fit a screw pressed firmly against the part to keep it in place. It needn't be the same thread as the fitting.

These sort of fixtures could also be used if you are just hacksawing lengths of tube off.

I've also held threaded parts in a collet to do work on the other end. With brass though it might flatten the thread a little. These seem to be taper threads as well so collets wont be very good. You could make the fixture out of a blank ended one though.

John

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Brian,

Thanks for the link;

That makes the whole question much more interesting: Cast Bronze, and Taper Threads.

I guess that the manufacturer has a rather clever automatic machine, and they come off like shelling peas; but it would certainly be a challenge to make these in modest quantities on the typical Home Worksohp machines.

MichaelG

As you are cutting parallel threads that makes things easier.

Take a length of 3/16 tube which you already have and thread one end for about 7/32" length, now cut off a 1/2" length of tube.

Make a holder by tapping a hole through hole in some scrap material at least 3/8" thick. and a screw with teh matching thread.

Screw your 1/2" length of pipe partly into the holder and a threaded rod or screw in from the other end to lock the pipe in place. Now thread the plain end that is sticking up out of the holder, undo locking screw and remove your now complete nipple.

J

PS Just a reminder Brian does not have a lathe

J

Edited By JasonB on 09/07/2015 21:05:36

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True; but his original question was "how do they do it?"

MichaelG.

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Something rather like this, but a little smaller [?]

MichaelG.

Brian also says he is finding it impossible to make his own. The note about not having a lathe was aimed at those who were suggesting methods that involve using a lathe

which reminds me of a government pipe specification..

Easily enough done without a lathe if you have the correct tap and die.

Drill and tap the thread into a block of steel to hold in the vice as a fixture to hold the threaded end of the pipe while it is cut to length and then threaded with the die.

The method MichaelG shows is almost certainly how they did it. The tricky feature is the fact that the thread is on a taper which rules out any form of fixed die.

I'd guess the only way you could make this in a home workshop would be using a taper turning attachment during screwcutting on the lathe. Unless you were to use a thread cutting milling cutter on a 4-axis CNC milling machine of course...

Murray

As I mentioned earlier he probably wont be able to unscrew the item from a fixture if he just screws it into a tapped hole and the runs a die down the other end for finish it. I mentioned a simple solution.

Taper dies and taps are available but tend to be expensive. Also die head chasers from other sources.

**LINK**

John

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PM RESEARCH sell 3/16-40 taper dies for $30. Even the non tapered pipe nipples had me stumped !

You don't live in Treasure Island Britain so can probably get all sorts of things cheaper than us. An expression some of us use to explain the rather high prices we have to pay for some things.

On the other hand I linked to that site because I knew that they were bound to offer them. They are probably gas fitter quality and may be cheaper elsewhere.

John

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