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Astronowanabe
10-02-2009, 02:48 AM
Perhaps a known trick but as I (re)discovered it, I will pass it along
threading pipe on a lathe is complicated by the fact the thread is on a cone
with a 1 deg 47 minute taper, the options I read about were:
1) Don't. Use a pipe threader, that is what they are for.
2) offset tail stock and turn between centers
3) back the cross slide off a certain number of thou per revolution

well, my part is not a pipe and won't fit in the pipe threader
I could turn between off set centers but it is a fiddley setup to get a dog on
a short piece and then would have to set the taper up properly
and restore the tailstock to center when done

manually backing the cross slide off on the fly
when there are already plenty of things to keep track of
while threading a short section seems like inviting a problem
especially if there are a number to do.

the way I found was to use a jaw from the pipe threading tool
as a form tool just as you would single point an untapered thread of the same pitch.
Clamp the tool parallel with the face of the chuck
and back it off & disengage the feed (in that order)
when it just becomes fully engaged.

http://ix.cs.uoregon.edu/~tomc/images/pipe_threading.jpg

Frank Ford
10-02-2009, 02:57 AM
Good going, schmarty! I have a pipe threading die set, and I'll try to remember this trick, you betcha.

macona
10-02-2009, 03:09 AM
You missed the fourth option. Use a lathe with a taper attachment.

Your technique here also works using taps as the cutting tool to cut the thread.

Braindead
10-02-2009, 09:41 AM
Nice.

I have a use for that TODAY :D

JCHannum
10-02-2009, 11:14 AM
Good use of a threading die.

While pipe threads are tapered, the stock is straight. Using the setover tailstock method will not produce the proper thread form. A taper attachment is about the only method of single pointing pipe thread. Backing off the compound will sort of work, but is a pretty iffy method unless leakage is not a problem.

madman
10-02-2009, 09:18 PM
I do all types of wacky threads and this pipe thread tip is going to become one of my No Pain No Brain setups. thanx for the idea.

motorworks
10-02-2009, 09:34 PM
"Your technique here also works using taps as the cutting tool to cut the thread."

? going to try it in the am as I have 6 1.250 pipe to do
for the son's girl friend's father... :)

JCHannum
10-02-2009, 10:13 PM
"Your technique here also works using taps as the cutting tool to cut the thread."

That could be made to work with a bottoming tap for screw threads, but I would not be too sure about the applicability for pipe thread unless the tap is used the wrong way around. With pipe thread, the thread on the tap gets shallower the deeper the tap goes in. You would need to do some creative fixturing and grinding of the tap to get it to work if it would work at all.

jeremy13
10-02-2009, 10:13 PM
I was going to post a topic on the same thing. We changed out the die teeth on our Ridged 300. Will any die number work?

gwilson
10-02-2009, 10:49 PM
The tap would have a right hand thread,but would be presenting the thread at backwards of its angle to the pipe being threaded. Maybe if you presented the tap so the cutting edge was presented very much downhill to the pipe,you could avoid most of the conflicting thread angle issue.

An old book I read described how you could make a left hand tap by trapping a rt. hand tap in a steel hole,and screwing a blank tap in beside it,which would come out left hand.

Astronowanabe
10-02-2009, 10:58 PM
I was going to post a topic on the same thing. We changed out the die teeth on our Ridged 300. Will any die number work?

I think which number die you use will matter about as much as at what rotation you happen to chuck the piece. probably not at all

I do not have a taper attachment and sorta lumped using one in with
off setting the tail stock since they both make tapers.
But now that you mention it I think I see why offsetting the tail stock and using a tap (placed at a 1.75 deg angle) although close is different from taper attachment or backing off the cross slide. (or a pipe threading die @ 90 deg)

with correctly formed threads they point out perpendicular from the axis of the pipe

with the offset tail stock and angle tap the thread peaks are canted forward (towards the end of the pipe) which I bet will work in a pinch if wrapped in high tensile bailing wire but are not technically correct.

Just wondering ... if both the external threads and the internal threads were made with the angled tap method the problem would be twice as bad wouldn't it.

tattoomike68
10-03-2009, 12:32 AM
3) back the cross slide off a certain number of thou per revolution

Thats litle runt ass pipe.

I used to thread some fire hydrant stubs ,id 8" pipe. I turn the threading tool uside down, run the lathe is reverse and thread away from the chuck and fudge the cutter in as it goes along to fake the taper.

at the last shop i worked at we had a die head that would do up to 6" pipe and the trick was to use the P70. 70 ton Piranha iron worker as a pipe vice.

that prick grab that some bitch and work got done.

.RC.
10-04-2009, 07:11 AM
Nice tip, I do a bit of pipe threading and usually just do a parallel thread...But I have single point threaded a piece of 4" pipe with the taper attachment on my 14" lathe...

Astronowanabe
10-12-2011, 12:06 AM
Hello Astrowanabe,

I've just noticed your tip on using a pipe die form to cut a tapered
thread.could you please answer a couple of questions if you don't mind.
1 - Does a taper still have to be machined on the part or
2 - is the thread taper built into the die.
I imagine that the die is tapered and that the thread is cut the same as
single point method matching the TPI on the leadscrew and using half nuts.
My main question I guess is do you just slowly take consecutive cuts
getting deeper to form the taper.

Thanks for your time Alan.


Hi Alan,
Sorry not to be able to answer sooner and directly as Chuck63 does not seem to exist as a member of HSM, and your question was obscured by 65 thousand empty messages in my inbox all attributed to you. Something between your Browser and the Forum software went a little wonky when you sent the PM I think.

1- I tried the method with and without the cutting the base taper first and found that for me, pre-cutting the taper was not what mattered.
Not tapering gave the cutter something to do while making the earlier passes. And cutting the taper did nothing to change the bottom line which is that, at the end of the last finishing cut, you have a HUGE form tool in contact (well for a 10" Logan with flat belts anyway).

2- Yes the taper is built into the die, so to set the correct taper you just align the back of the die parallel to the chuck face by any means you like.

Yes it is just as you imagine, the only thing you may not have suspected is
how big the end of that final cut gets... don't use a small 3-jaw chuck, if you have a larger 4-jaw.