I've not fully thought this through, and it's too cold in the workshop now, but would it need to be a left hand chaser to cut on the front of the hole, or a conventional one to cut on the rear, with the lathe running backwards?

I'm thinking about the helix angle of the teeth, but maybe not thinking hard enough.

Bill

If you need modify the chaser, especially as Andrew describes by turning into a single-point tool, you are giving yourself extra work and ruining the thing for its intended use.

Use a proper internal-thread cutting tool, either singe-point or an internal chaser.

There is though an old dodge as a chaser, of using one flute of a tap held in a holder like that made for round-section boring-tool shanks. This of course for diameters much larger than the tap, but with the same thread-form and pitch.

Seems like it would be much easier to use a tap clamped in a holder whole, or a section cut from a tap and silver soldered to a boring bar shank, to cut an internal thread. That is what taps are designed for: internal threads. Clearance angles and helix angles will be correct for an internal thread.

Does my head in trying to imagine it from the armchair, but it seems to me that the helix angle on a die head chaser will always be wrong in relation to the cutting edge for cutting an internal thread.

Seems to me it's way more trouble to mount the chaser – or part of it – than to grind a singlepoint threading bit out of 1/8 or 3/16 square HSS to fit a vanilla boring bar, gauging the flank angle from a suitable pitch gauge and stoning a flat or radius on the tip as appropriate to the thread form. But perhaps we all have a preference for the methods we're used to.