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Thread: Pipe threads on a lathe

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    Bassbum2's Avatar
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    Default Pipe threads on a lathe

    Can pipe threads be cut on a lathe with a taper attachment?

    Russell

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    SBLatheman's Avatar
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    Yes.......

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    Cool

    That is the best way to cut them. I have read in other forums where guys cut pipe threads without a taper attachment but that really isn't the right way. I worked in a shop doing contract work for a pump company and we made their tapered pipe. The threads had to be cut in a lathe and they supplied a go no go gage that had to fit properly. Some threads were tapered on the end and a straight thread for a foot or so for an adjustment nut...Bob
    Bob Wright Metal Master Fab
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    What I would be doing is making adapters for pressure testing cylinders. Some of them would be a straight thread and some a pipe thread, some will also be metric.

    Russell

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    Bruce Nelson is offline Stainless
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    Set the taper attachment at 3/4 inch per foot taper. First machine a taper on the end of the pipe to the dimensions given in Machinerys Handbook. Then set the quick change gearbox to the number of threads per inch required. Then, cut the thread to fit whatever gage you have, or to specs given in the Handbook. Be prepared to withdraw the threading tool with the cross-feed handwheel at the end of the thread.

    If the thread is for common pipe joining use, machine the thread to a depth where the flat on top of the thread (crest) just disappears. If you don't have a sharp on the crest of the thread, the thread won't seal when internal pressure is applied.

    Threads for mechanical fasteners should have a flat on the crest of the thread equal to on-eighth the pitch. There should be no flat on the crest of a pipe thread, which are meant to be self-sealing. (Note that when you cut 11 1/2 TPI, you will need to engage the threading dial on the same number.)

    Metric threads would require transposing gears. I have never cut metric pipe threads before, but I would think that you would have to reverse the spindle at the end of the cut to return the tool to the beginning of the cut. (or have a lathe that cuts metric threads)

    Lord Byron

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    Quote Originally Posted by Bruce Nelson View Post
    (Note that when you cut 11 1/2 TPI, you will need to engage the threading dial on the same number.)
    Correction:
    For half threads, egage when the thread dial is on an odd number, or a half turn of the dial.
    For 1/4 threads, engage on the same number.
    Ted

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    Bruce Nelson is offline Stainless
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    Depends on the lathe, leadscrew, and threading dial gear. Same number would be safest.

    Lord Byron

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    J.R. Williams is offline Hot Rolled
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    Default Pipe Threads

    Many lathes cannot cut the smaller pipe threads such as the 1/8"-27. Most will cut 28 TPI. I leave my taper attachment set for 3/4"/ft and take a ight cut with the taper attachment before cutting the thread. Are the "metric" smaller pipe threads the old British Standard series?

    JRW
    S_W_Bausch likes this.

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    I am not sure sure what the metric threads are yet, I am waiting for more details. My friend comes across metric stuff from time to time when he does inspections and testing on ships. Most likely when he comes across one is when I will find out what the details are.

    Russell

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    Clive603 is online now Titanium
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    Quote Originally Posted by J.R. Williams View Post
    Are the "metric" smaller pipe threads the old British Standard series?JRW
    My understanding is that the BS pipe thread was adopted for what might be called "plumbing type" work. For specialist and engineering applications where either the designer was feeling antsy or the spares department wanted to get a lock on parts supply something out of the ISO constant pitch series lists would be most likely. Parallel only so far as I know.

    Clive

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    TimW(PA) is offline Aluminum
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    My first project on my lathe was fixing my tailstock handwheel. I used pipe threads during the project. My method was fairly untraditional to say the least, but was effective. The thread is here:

    First project: Fixing tailstock handwheel

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    Default Youtube

    I think I remember Tubalcain having a video on Pipe Threading on a Lathe there. I enjoy his videos a bunch.

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    I have already watched most of his video's and the one on pipe threading is done with a pipe threading die. I will need to do metric threads but I am not sure if they will be straight threads and seal with an O ring or be tapered threads.

    Russell

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    oceanpout is offline Aluminum
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    another way to do it with out the taper at. is to rough cut it staight leaving oversize then finish with a die.

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    Quote Originally Posted by oceanpout View Post
    another way to do it with out the taper at. is to rough cut it staight leaving oversize then finish with a die.
    The threads will most likely be metric and as I stated before, I don't know if they will be straight or tapered so I will not have a die handy and probable wouldn't have time to order one. When a ship comes in and needs service, there is very little time to get things done. It just might be something I will have to turn down as I most likely won't have the time to figure out how to get the job done before it is needed. I will post if I do end up making an adapter and let everyone know how it worked out.

    Russell

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    S_W_Bausch is offline Diamond
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    Quote Originally Posted by J.R. Williams View Post
    Many lathes cannot cut the smaller pipe threads such as the 1/8"-27. Most will cut 28 TPI. I leave my taper attachment set for 3/4"/ft and take a ight cut with the taper attachment before cutting the thread. Are the "metric" smaller pipe threads the old British Standard series?

    JRW
    Bingo!

    I have stumbled upon a great guy to appraise potential purchases, and while he was looking at one lathe, he was remarking upon the presence of "pipe threads".

    He pointed out "27 TPI", and a few others.

    I just keep quiet and let him play with the machine

    If someone wonders "which lathe", it was a 14x40 Rockwell vari-speed [or is 14x41?].

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    Quote Originally Posted by Bruce Nelson View Post
    .... Be prepared to withdraw the threading tool with the cross-feed handwheel at the end of the thread.
    Lord Byron
    Hello. I'm trying to turn tapered pipe threads on my 10L with a taper attachment.

    When I reach the end of the thread, I have to quickly loosen the lock lever on the taper attachment, quickly withdraw the threading tool with the cross-feed (not the compound) then disengage the half nut.

    Am I doing this part of the operation correctly?

    Thanks for your help.

    Mitch Smith

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    Default Taper attachment

    As I recall there are 2 types of taper attachments. The telescopic type allows you to still use your cross slide. I think with yours you need to use the compound to move the tool in and out and leave the cross slide clamped. Once the clamp is loosend you will lose your reference point for the thread.

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    Thanks for clearing that up for me Ferrous.
    I forgot about there being two types of taper attachments.

    So with that in mind, I guess I still need lots of practice.

    My next issue which happens fairly often is the need to make short pipe nipples. Everything from a close nipple to about 5" length.

    The only idea I've come up with is to use an expanding mandrel between centers. Haven't had a chance to try it yet.

    Mitch

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    LarrySB13 is offline Plastic
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    Quote Originally Posted by SBLatheman View Post
    Correction:
    For half threads, egage when the thread dial is on an odd number, or a half turn of the dial.
    For 1/4 threads, engage on the same number.
    Ted
    I have found that cutting pipe threads or just about any thread it is better to just leave the half nut engaged back off the compound and reverse the lathe back to the starting point.

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