cnc tapping Re: General Tool Life Question

--- In CAD_CAM_EDM_DRO@y..., Fitch R. Williams <frwillia@m...> wrote:
Fitch,

There are three ways to "automatically" tap in a machine.

1)Standard "manual" tapping head (often modified by the mfr. for cnc
operation; i.e., so it fits in toolchangers and uses a
shorter "torque" arm, or is modified so that the use of such an arm
is not necessary.)
2)Floating holders, interpolated motion
3)"Rigid tapping"

The manual type tapping head can be used on cnc machines with "loose"
control of the spindle to feed relationship. The large end-float
ability of these heads allows the tap to work as it does in the
manual mill or drill press. The programmer just needs to get "close
enough" in spindle speed vs. feed to prevent the conditions you
outlined. The down side of this approach is that there is less
control of tap depth, and looser tolerances are required here.

Floating holders are generally used in commercial CNC tapping.
This "end-play" allows for the possibility of the spindle and feed
not matching precisely. However, this holder does not allow the same
latitude that the manual head does, so the feed and spindle need to
be "close" to correct.

Rigid tapping is an option on many cnc machines (usually at fairly
high cost). This is a machine capable of EXACTLY matching spindle
rotations to feed, so a floating holder is not NECESSARY. Which is
why it is called "rigid" tapping.

Hope this helps.

Ballendo

> Case 1: This seems like the worst case. Spindle RPM is slower (for
> whatever reason) than the tap needs to keep up with the selected
feed
> rate. In this case the spindle will over run the tap and push
(hard) on
> the tap. It might damage something.
>
> Case 2: RPM is faster than the tap needs to keep up with the feed
rate.
> In this condition, the tap will gain on the spindle - the tap will
pull.
> I would think that if this is the case the tapping head would
reverse or
> disengage (?) momentarily then re-engage and keep tapping.
>
> Case 3 is when spindle speed and feed match, but that one takes
care of
> itself of course.
>
> With that as a background, I have some question and would be
interested
> in your experience with this. The questions are: Does case 2 work
as I
> described? If so, do you always make sure your spindle is a bit
faster
> than required so that you are operating as described in case 2? If
so,
> how much faster?
>
> Fitch