The tap itself is made from a drop from the scrap bin, material unknown.
The thread form tooling is made from ends of small snapped taps, I grind them on a homemade tool grinder made from an old valve grinding machine, The threading tool fits in a homemade tool holder onto my QCTP.
I do not grind a flat on the end, nor did I grind a helix angle on it, for a 26TPI .636 dia it would have been minimal, the sharp-V seams to cut better especially on hard material like stainless, this was carbon steel and while cutting some of the first passes it tends to be rough but getting close to thread depth ( .031 in this case) it smoothed out, the spindle was in back gear low-rpm.
The tube you see is stainless steel instrumentation tubing, its .750 od I forget the wall but it's pretty thin, too thin to accept the thread so I inserted a previously made steel threaded sleeve and secured it with Loctite extra strength.
The sleeve, I load a steel blank in the chuck bore it out to size and thread it with the same form threading bit held in a small diameter homemade boring bar, because the diameter of the boring bar is small the spring is amplified so I tend to spring cut three times each to eliminate it, once the depth has been achieved I put it onto a threaded mandrel and turn it down between centers to get the od of the tube, remove and arbor press into place with Loctite.
This tap I made is really a chaser, this is allowing me to slightly under cut the thread cutting and I don’t have to worry about getting the desired size which is time consuming, I get it really close I finish off the final size with this tap.
Anthony.
