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Tapping 3/4 pipe threads in 416 Stainless

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  • Tapping 3/4 pipe threads in 416 Stainless

    This has been harder than it should have been. I turned the proper taper but my tap used mostly for cleaning up threads in existing fittings has seen better days. Looking at new taps, there is an Interrupted thread tap which supposedly takes less force to drive. Has anybody used this sort of thing?
    Byron Boucher
    Burnet, TX

  • #2
    Pipe Tap

    I have used those for 1/8, 1/4 and 3/8. They work pretty well. I haven't done a 3/4, but based on the other sizes it seems like a good way to go. For larger size threads I just use a thread mill in the CNC. That's a lot easier than trying to twist a large tap or die.


    • #3
      I've used an interrupted-thread pipe tap in brass and found it to be much easier. It was I think 1/4" NTP, but I don't see why the decrease in force required wouldn't carry over to 3/4".

      Just be sure it's a GOOD tap and be prepared to pay for it. McMaster-Carr gets 99 dollars and change for a 3/4" NTP interrupted-thread tap.
      Try to make a living, not a killing. -- Utah Phillips
      Don't believe everything you know. -- Bumper sticker
      Everybody is ignorant, only on different subjects. -- Will Rogers
      There are lots of people who mistake their imagination for their memory. - Josh Billings
      Law of Logical Argument - Anything is possible if you don't know what you are talking about.
      Don't own anything you have to feed or paint. - Hood River Blackie


      • #4

        Not quite sure if I follow this, but are you using an HSS tap? I started out many years ago with carbon steel taps, couldn't believe the difference when I switched to HSS taps.

        All of the gear, no idea...


        • #5
          A 3/4" tap is a pretty substantial piece of kit. Would it not be possible to touch it up with careful use of a hand grinder and a large chainsaw stone?
          Duffy, Gatineau, Quebec


          • #6
            Also experiment with different cutting fluids, they can make a big difference.
            Best i have found is 75% trike and 25% ATF or light hydraulic oil to stop the trike evaporating too fast.

            I know trike is banned but it still exists in SOME weld splatter sprays and brake cleaners.

            Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.