cnc tapping Re: General Tool Life Question

--- In CAD_CAM_EDM_DRO@y..., "imserv1" <imserv@v...> wrote:

> I actually class a 4th style. that is the Floating holder ,...
>with
> release. A floating holder can tolerat both tension and
>compression
> so that if your spindle is too slow or too fast, neither condition
> will break a tap. Think of a lathe with change gears and no
> synchronization between the spindle speed and the CNC controls on X
> and Z axes.
>
> If you have a programmable reverse on the spindle, you ***might***
> be able to reverse it in time to prevent breakage with a floating
> holder. However the speed at which you could tap would be limited
>by
> the ability to stop the spindle and make a reversal. In order to
> compensate for this many Turret lathes had a floating holder that
> would release when pulled out say 1/4 inch from the holder. This
> would happen when the tailstock was fed to a stop and the spindle
> continued to turn. Once the tap holder was released(thus starting
> the tap a-spinning), the spindle was reversed and the tap backed
>out
> with no breakage. Since the demise of the turret lathe, there are
> thousands of these floating holders with release "floating"
>around.
> They are often too large, but I see a smaller on once in a while
>that
> could probably be adapted to a benchtop mill. Somebody could
> probably design one for a sherline(cnc or not) and make a
>fortune. ;-)
>
> Best Regards,
>
> Fred Smith

Fred's correct on this.
Up until last year I used to run a small Myford C7 capstan lathe
making laser cutting nozzles. That's all this machine ever did.
Because the thread was very fine, short and in copper I couldn't use
a coventry die head because as it pulled to release it ripped the
threads. So I had to use a conventional die.
I made one of these floating holders up. Ok it was for a die but the
operation is the same.
It was driven by two pins on the fixed shank butting against two pins
on the back of the die holder. It was fed on and helped along, at the
end of the thread it carried on and pulled off the pins. This then
caused it to rotate free at spindle speed. The die holder was mounted
on the fixed shank on a one way needle roller clutch combined bearing.
Once the spindle was reversed the die holder was locked back on the
fixed shank and backed off.
I can't take any photo's as the machine was sold last year when the
contract ended but I could sketch it up if needed.

John S.