For manually tapping with my benchtop drillpress (up to 3/8") I've ground
flats on a set of taps with a die grinder.. not exactly accurate, but close
enough to be reliable (still rotating, not orbiting the center axis of the
spindle.

Chucks aren't much good for holding taps, IME, except for small taps held in
a portable drill for tapping in relatively thin materials (electrical panel
mounting plates, etc).
These methods are definitely not accurate enough for a rigid CNC machine, or
any rigid machine/power tapping method without a tapping head or similar
accessory.

It shouldn't be extremely difficult to modify some collets to engage the
square tang at the back end of taps, by adapting them with some fairly
readily available round items that have fairly-well-centered square holes in
them.. square drive sockets come to mind, for 1/4, 3/8 + 1/2" square holes.

Other metal parts that have square holes that I've seen, are some plumbing
fixture parts.. there are likely more, if one looks around thru junk
drawers.

The inside surfaces of collets aren't generally precision ground, but are
likely to be close to concentric with the outside surfaces, so adapting a
collet with a part which has a square hole shouldn't be difficult for anyone
with a lathe.

The center piece could possibly be pinned, pressed, TIG'ed or secured by
some other means to keep it from rotating.

The holes in the part to adapt to the square tap tang wouldn't have to be
square (if you can't drill square holes).. it could be a slot that engages
two sides of the tang, since the collet would provide the proper centerline
alignment.

How hard could it be? (Top Gear)

--
WB
..........


"Ignoramus25538" wrote in message
...
My CNC mill does rigid tapping and it is great and easy to do -- just
one "one liner" like this

G33.1 Z[-0.5] K[1/24]

would rigid tap a 24 TPI thread from the current point to the depth -0.5.

Easy and powerful.

It even works great with fine threads, but I have a problem with
coarse threads. I hold the taps in a Jacobs drill chuck. The chuck
cannot hold a coarse tap, like 1/4-20, the tap slips in the chuck. The
result, is holes that are partially tapped and a slipping tap. Not the
end of the world, but I want to do better.

What kind of tool holder should I use for this rigid tapping? Would
colleted tool holders help with this?

i