Using a tap as a thread boring tool - video

[Frank S]

Perhaps I have miss-understood what you said but we need to be a bit careful here. I can see being able to chase threads already cut. But, if one attempts to cut a full thread, using a tap as a boring device where only one flute of the tap is touching the work, I doubt very seriously you can do that in one pass.

While it is true the tap cuts in one pass. It is not true that a single tooth cuts the full thread in one pass. A taper tap, that can cut a full thread through a hole is tapered, so as you get started, each tooth cuts makes a tiny chip, getting cutting the thread deeper as you advance the tap. It also cuts on all sides at the same time so the load is centered equally all around the body of the tap.

A good way to guard against breakage is to make a fitted sleeve over the tap encapsulating the shank and at least the bottom and back thread runs
What I would do would be to bore a piece of round stock to fit the shank then bore out the thread depth slice away about 120° of the now threaded end the length of the threads. Mow screw the tap into the holder. shank first once it is threaded all the way in drill and tap for a couple of grub screws to contact in the flutes clamp this in your boring bar holder or tool holder, you now have made a tool you can thread with without breaking the tap.