I use an ER32 chuck in my mill that has VFD. I set it to low RPM for tapping, and use the instant reverse to withdraw and/or break the chip. I know I'm tempting fate, but I've not had a tap break – yet. I've broken taps when doing it free-hand but not yet with the mill.

I don't tighten the chuck too much, so, with a bit of luck, it will slip if the torque gets too great. I've been lucky so far.

"It just holds a tap and is not an automatic tapping machine with reverse etc. At the front of the chuck are the jaws to keep the tap concentric and at the back of the jaws are a pair of flat jaws to grip the square on the end of the tap."

A fair description, Speedy Builder5, but I find my similar device excellent. Mine is arranged to slide on a rod held in the tailstock and has been equipped with a fixed tommy bar. It has a claimed range of M4-M16 but, of course, this depends on the shank and square sizes of the tap.

By the way, I am a Speedy builder, too, but mine is a recumbent tricycle!

Yes, at tapping speed, ie. less than about 120rpm, switching into reverse takes far less than 1/4 rev. so its effectively instant. At that slow speed there is no perceptible ramp time.

Chris Denton:

Good luck with your build. I'm glad that you have not been deterred by the less positive posts. My photo shows my chuck tapping a short thread in a blind hole supported by a sliding holder in the tailstock; whilst the tap cannot slip in the chuck (unlike a drill chuck) the moment the tap starts to bottom, the tommy bar is released and the lathe spindle halted thereby avoiding the other danger of a broken tap.

Frances IoM:

Sorry if I wasn't clear about this. The tommy bar is held in one hand and the tap advanced into the work on the sliding support until it starts to cut whereafter the tommy bar is simply used to resist the cutting torque. Once the spindle has been halted the lathe is put into reverse and the tap withdraws onto the sliding support; any tendency for the chuck to rotate is again resisted by lightly holding the tommy bar.

Essentially a manual operation, but with clear advantages over the use of a drill chuck in the tailstock.

Correction: the stated capacity is M4 – M12 but in practice the chuck will not close down sufficiently to hold the shank of my M4 taps and, yes, I have used a drill chuck with these!

Bazyle:

Fair comment, although if I am too slow in stopping the spindle the plastic ball is not going to damage the bed but only my fingers!

The reason for making the tommy bar of reasonable length was that I also use the chuck on my larger lathe where there would be full and unimpeded rotation; I wanted to have enough leverage to resist the torque of tapping large coarse threads on the bigger machine.