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View Full Version : Tapping 3/4 pipe threads in 416 Stainless



Boucher
06-24-2012, 02:28 PM
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?

Toolguy
06-24-2012, 02:32 PM
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.

SGW
06-24-2012, 03:38 PM
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.

Ian B
06-24-2012, 07:30 PM
Byron,

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.

Ian

Duffy
06-24-2012, 07:32 PM
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?

John Stevenson
06-24-2012, 07:44 PM
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.