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HomeCNC LatheHow to Cut Single Point Taper Pipe Threads on a CNC Lathe

How to Cut Single Point Taper Pipe Threads on a CNC Lathe


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Pipe threading 101. Learn how to cut single point taper pipe threads on a CNC lathe.

NWTC’s Matt Schmelzer will go through the programming and specifications before loading the programming and cutting the pipe threads. To complete this lesson you will need the Machinery’s Handbook, scientific calculator and pipe thread gauge to measure the final threads.

00:00 Introduction
01:00 Thread specifications. Use Machinery’s handbooks to find necessary dimensions to program the threads ((https://amzn.to/3BOSJdU)
03:30 Specifications demonstrated in drawings.
06:00 Dig deeper into the implications of those specifications.
07:02 Canned cycles breakdown
09:55 G-code for the application
11:53 Program is loaded in the machine, let’s make some threads!
12:15 Metal cutting!
12:40 How to use a national pipe tapered gauge to measure the threads.

Have any questions about single point tapered pipe threads? Or some tips and tricks for cutting these threads? Drop them in the comments below!

Matt Schmelzer is the CNC instructor at Northeast Wisconsin Technical College. To learn more about the manufacturing programs at Northeast Wisconsin Technical College visit

Follow Matt’s machining program on Instagram here: https://www.instagram.com/nwtc_cnc_machine_tool/

Stay tuned for more videos!

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  1. If you're going in an extra .100 (-.8815), wouldn't you're starting point be at Z.1 instead of Z.2? Doesn't that change your taper if you don't, or am I missing something??

  2. I tried your code on a simulation software and it cuts threads but the taper was inverted? I had to change the second line R value to a positive instead of negative. Is this a value that can change because of certain machines? Or is the sim wrong? ?

  3. Am I the only one who thinks this is wrong? I get about .812" for the starting point of the OD by adding the mean thread height to E0(pitch diameter at beginning of external thread). and a taper length of about .442(which falls in between the L5 and L2 points. L5 is supposed to be the last complete thread and beyond that the truncation at the crest grows. by turning the front down to to only .791 I don't see how this doesn't put the thread height and truncation completely out of tolerance even though a proper pd and root means it would still pass the L1 ring gauge. Maybe it doesn't matter so much for a normal npt but I'm thinking an nptf would never dryseal doing it this way.

  4. Just the other day I had to cut some 1/8 NPT plugs on a 90s era CNC hardinge. Used the two block G76 with the R value. No one else in the shop knew how to operate that lathe because they only know the guide i control. Really does pay to know your G code out in industry!

  5. Thanks for this Video Very nice and simple explanation
    just another easy way to calculate the dimeter (X value) of the start thread ( 3/4=0.75 divide by 12 =0.0625 * (0.7815+0.2)=0.06134
    subtract from OD 0.840 – 0.06134=0.7786 . no need to calculate the angle and trigonometry to obtain X value of the start thread

  6. My shop used 1/8-27NPT for a grease nipple on pivot arm for a Shuttlewagon. The machinists before me had a ground tapered reamer before the tap. But upon closer inspection the reamer wasn't doing anything at all! Then I found out for 1/8-27NPT you don't need a reamer. Cut down some of that cycle time!

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