Re: [CAD_CAM_EDM_DRO] cnc tapping Re: General Tool Life Question

I don't believe you gain a thing by rotating both the headstock and the
tool. Your procedure will work just as well without rotating the tool at
all. Slow the headstock speed all the way down to the required difference
and you'll accomplish the same thing. The procedures works just as well in
a manual lathe with a stationary tool as well as in the mill with the work
being stationary.

There are several 'secrets' to this which eliminate the need for exact speed
matching:
1. Rotate the spindle at a slower rate...about 60 RPM or less. This will
reduce overtravel when forward feed is stopped.
2. Sliding movement of the tap compensates for mismatch between feed
rate/RPM mismatch.
3. Stop the forward feed before reversing the spindle rotation.
4. Use a properly designed tool holder.

Smoke

> Rigid tapping as it is done on most cnc lathes relies on speed
> differentials. The work is spinning in the chuck but the tap is also
> spinning in a powered spindle in the 'tailstock'. They both revolve in the
> same direction but to tap a hole, the tailstock spindle speed is increased
> and to back the tap out, the tailstock spindle speed is reduced. This is a
> bit safer method than trying to adjust feed of the tap towards the work

(in

> this method the tap is free to slide in and out of its spindle and the

only

> feed is to bring the tip of the tap into contact with the work) especially
> if there is friction control on the tailstock spindle so that it can slip

if

> the tap bites too hard.
>
> Ian
>