On 2010-09-27, Jon Elson wrote:
On 09/27/2010 12:40 PM, Ignoramus21149 wrote:

I wrote a G-code subroutine to do it. To run safely, it MUST have a
floating tap holder that can take up the slack of the tap that moves
off position, while the spindle is reversed.

(Tap a hole with a floating holder)
Otap_with_floating_holder sub
#depth = #1 (Hole Depth)
#tpi = #2 (Threads per Inch)
#rpm = #3 (RPM of the spindle, EXACTLY MEASURED)
#safez = #4 (Safe Height)

#frate = [#rpm / #tpi]

M3 (Forward)
G1 Z#depth F#frate
M4 (Reverse)
G1 Z#safez F#frate
M3 (Forward again)

Otap_with_floating_holder endsub
M2

Well, this all SOUNDS good, but in fact, there is NO connection, at
all, between the spindle and the Z feed.

The only connection is that I measure the speed of the spindle with a
handheld tachometer, and then calculate the feed.

You'd have to do the first test holes carefully to make sure you get
the desired depth of tapping. The spindle is running at whatever
speed it is, and the Z infeed goes at the programmed rate. But, at
the end, it is only the Z depth that determines when to reverse.
NOT, the number of turns the tap has fed into the work.

Absolutely.

Still, this is likely to work, assuming the springs on the tap holder
are strong enough to start the tap into the work promptly.

And, you won't believe what a MESS this will make, if you ever mess up
and have the spindle running at the wrong speed for the calculated
feedrate. been there, done that!

What will happen, it will tear the tap out of the collet?

Anyway, obviously rigid tapping, optionally with the floating holder,
is the way to go.

i