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

[Brian JohnParticipant @brianjohn93961]

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 ?

[Brian JohnParticipant @brianjohn93961]

The parts are too small to grip in the vice !

[Martin KyteParticipant @martinkyte99762]

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

regards Martin

[Brian JohnParticipant @brianjohn93961]

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.

[IanTParticipant @iant]

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

[IanTParticipant @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

[jason udallParticipant @jasonudall57142]

Not much help to op but as production ( down to 4mm dia 2 mm od in 316 SS).. we regularly made nipples ( thread—parent metal —thread) parts by screw cutting in “middle of bar “and parting off through threaded portion to seperate… slow in production terms since you have to allow for acc’n decc’n of tool to reduce /minimise thread runout ..its easier to keep up if you keep the rpm down to say 1000…
Its just how we did it. .10, 000 at a time.

[jason udallParticipant @jasonudall57142]

Of course the above should read ” 4 mm dia 2 mm ID”

[Brian JohnParticipant @brianjohn93961]

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

[AjohnwParticipant @ajohnw51620]

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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[Michael GilliganParticipant @michaelgilligan61133]

Posted by Brian John on 09/07/2015 14:26:51:

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

**LINK**

.

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

[JasonBModerator @jasonb]

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

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 09/07/2015 21:04:07:

PS Just a reminder Brian does not have a lathe

.

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

MichaelG.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by Michael Gilligan on 09/07/2015 20:38:18:

I guess that the manufacturer has a rather clever automatic machine, and they come off like shelling peas;

.

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

MichaelG.

[JasonBModerator @jasonb]

Posted by Michael Gilligan on 09/07/2015 21:14:08:

Posted by JasonB on 09/07/2015 21:04:07:

PS Just a reminder Brian does not have a lathe

.

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

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

[russellParticipant @russell]

Posted by jason udall on 09/07/2015 13:05:14:
Of course the above should read " 4 mm dia 2 mm ID"

which reminds me of a government pipe specification..

GOVERNMENT PIPE SPECIFICATIONS

1. All pipe is to be made of a long hole, surrounded by metal or plastic, centered around the hole.
2. All pipe is to be hollow throughout the entire length – do not use holes of different length than the pipe.
3. The I.D. (inside diameter) of all pipe must not exceed the O.D. (outside diameter) – otherwise the hole will be on the outside of said pipe.
4. All pipe is to be supplied with nothing in the hole, so that water, steam or other stuff can be put inside at a later date.
5. All pipe should be supplied without rust – This can be more readily applied at the job site. Some vendors are now able to supply pre-rusted pipe. If available in your area, this product is recommended as it will save a lot of time on the job site.
6. All pipe over 500 feet (153m) in length should have the words “long pipe” clearly painted on each end, so the Contractor will know it is a long pipe.
7. Pipe over 2 miles (3.2 km) in length must have the words “very long pipe” painted in the middle, so the Contractor will not have to walk the entire length of the pipe to determine whether or not it is a long pipe, or a very long pipe.
8. All pipe over 6” (152 mm) in diameter must have the words “large pipe” painted on it, so the Contractor will not mistake it for a small pipe.
9. Flanges must be used on all pipe. Flanges must have holes for bolts quite separate from the big hole in the middle.
10. When ordering 90 degrees, 45 degrees or 30 degrees elbow, be sure to specify right hand or left hand; otherwise you will end up going the wrong way.
11. Be sure to specify to your vendor whether you want level, uphill, or downhill pipe. If you use downhill pipe for going uphill, the water will flow the wrong way.
12. All couplings should have either right hand or left hand thread, but do not mix the threads – otherwise, as the coupling is being screwed on one pipe, it is unscrewed from the other.

[HopperParticipant @hopper]

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.

[MuzzerParticipant @muzzer]

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

[AjohnwParticipant @ajohnw51620]

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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[Brian JohnParticipant @brianjohn93961]

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

[AjohnwParticipant @ajohnw51620]

Posted by Brian John on 10/07/2015 09:33:04:

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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[Brian JohnParticipant @brianjohn93961]

John : most of my model engineering supplies and tools come from the UK with a few from the US.

[MuzzerParticipant @muzzer]

Posted by Brian John on 10/07/2015 12:04:02:

John : most of my model engineering supplies and tools come from the UK with a few from the US.

Indeed. Until I moved back to the UK from Canada last year, I found it was often cheaper to buy stuff in the UK, even after allowing for tax, duty and carriage. That was true even for Chinese and Indian tools. I suspected this was due to protectionist import duties (into N America) and the fact that locally made tools ("Made in USA" stickers everywhere) were often of indifferent quality but still damned expensive (those stickers must be expensive), thus providing a high floor price for competing (imported) low end products.

I'm aware of the existence of pipe threading heads, manual or powered but for either serial production or workshop one-offs, neither these nor split die are going to be much use to you when it comes to making a double-ended tapered pipe thread.

[Michael GilliganParticipant @michaelgilligan61133]

Posted by JasonB on 09/07/2015 21:04:07:

As you are cutting parallel threads that makes things easier. … < etc. >

.

Jason: A variation on your theme, if I may …

Brian: Although you do not yet have a lathe; I believe that you do have a drilling machine [if not, then please ignore what follows]

Instead of a plate; tap a piece of suitable tube, long enough to fit securely in the drill chuck [this may require some initiative, such as silver-soldering a sleeve over a shorter piece] then proceed as Jason suggests.

With the drill unplugged: lay the die-stock on the drill-table and use the machine as a "pillar tool".

I would recommend hand-holding the die-stock, rather than clamping it, because that way it can "float" and accommodate any error of concentricity in the workholding.

MichaelG.

[AjohnwParticipant @ajohnw51620]

Can't agree Muzzer. Brian already makes longer one and has a die so the problem is holding an end that has been threaded while he does the other end on rather short ones..

If he taps a hole in something to take the threaded end he has done he can handle shorter lengths. It will probably make it easier to do longer ones as well. He may have to buy an NPT tap or may already have one. Personally to be sure of being able to easily remove the part I would drill right through what ever he chooses to tap and open out most of it to a size to suite some suitable screw and tap that section for this screw, the rest for the part. This way he can lightly screw the part he is making in it's end and then hold it firmly firmly in place with the screw – sort of lock screw arrangement using the same principle as lock nuts.

Michael touches on an interesting point. I sometimes use a drill chuck to hold things for hand work. He might find it will bruise the thread that he has done when it's tightened sufficiently to hold the part while the other end has the die run down it. A bit of suitable rubber tube or a couple of wraps with masking tape might help with that.

As to how THEY make them. A cnc machine could make them in one go. If they used capstan type techniques, one threaded end while on the tube, part of and place in a fixture and thread the other end. The fixture might be a collet or something along the lines of what I described above or earlier. If they make millions it can be very surprising how well parts can be orientated and placed in machines automatically. In that case one machine would thread one end and part it off, then on to another machine to thread the other end. All sorts of things are possible even automatic transfer of the part from one machining operation to another on the same or another machine. I get the impression that some brass fittings are initially cast so I'd guess the industry has this sort of thing well sorted out using special purpose machinery some of which might have more than one spindle.

John

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