Re: Rigid Tapping--How is this accomplished?

For that size range- I'll tell you what I am doing. Take it
with a grain of salt- but it works like a champ for me...

I can't actually post the code we use, but here's the nutshell.

Tool change to a morse adapter, morse adapter contains a tap
driver, and also a tap. 3/8" spiral point coated for this
example...

Spindle forward at 60 RPM, flood coolant on, z down through
the hole.

Stop the Z motion and stop the spindle rotation. Z stops
instantly, spindle coasts to a stop. It probably only turns
maybe 2 rotations as it is in low speed (reduction) and has
the drag of pushing the tap through it. The tap *will*
continue to thread ahead in the material for those couple of
coasting turns. The square shank of the tap pulls forward a
bit from the holder. Still stays engaged though, no problems
there.

deliberately pause in the code so that the spindle is
guaranteed to stop.

start the spindle in reverse, and Z-up. Same way the tap
follows up. The axial (z) travel in the holder lets the
tap go back up while the spindle is coming up to speed.
That whole acceleration profile is compensated by the slip
in the holder.

How well does it work?
I used to spend 2.5 hours hand tapping each part (18 holes,
3/8-24, in 4140 CrMo). I would break a hand tap every 25
holes or so.
Using the tap holder setup, I can thread the same part in
about 6.5 minutes, and lost a tap every 100 or so. Backing
the spindle speed (and Z) off a bit, I ran an entire shift
on one tap...

Spiral flute taps are great! I will take them anytime over
hand taps. NO QUESTION! Much stiffer !!

-Damon

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Kim Lux <lux@d...> wrote:
> On Mon, 2003-10-20 at 11:06, doug98105 wrote:
>
> > Kim,
> >
> > Spindle coasting isn't much of a problem on coarse threads since
you
> > have the torque of the tap acting as a spindle brake. It's the
10-
> > 32's and smaller where there's very little torque involved.
>
> Good point. Like I said, I haven't done it, yet anyway.
>
> > Yes, a 10tpi doesn't have much room to coast with a tension
holder,
> > but I don't think you'll be able to tap the coarse pitches like
that
> > anyway. Check the tapping capacity of commercial machines
sometime,
> > it's always smaller than you'd expect based on the spindle hp.
>
> We'll thread mill the big threads anyway. I'd just love to CNC the
> 1/4-1/2" threads. That is where most of ours lie.
>
> > Another type of tap holder I use in the CNC lathes is a releasing
> > type, once the depth is reached and feed stops the tap self feeds
> > slightly more and then spins freely. By reversing the spindle the
> > mechanism catches again and screws the tap out. These have a
> > slightly less axial movement than the usual tension/compression
> > type. I'm not sure if these work in a mill where the holder is
> > rotating as opposed to the lathe where the holder is stationary.
>
> Can you recommend a brand of these ?
>
> > Doug
> >
> >
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