Re: [CAD_CAM_EDM_DRO] Re: General Tool Life Question

On Thu, 17 Jan 2002 07:10:27 +0000, Jon Elson <elson@...>
wrote:

>I use a Procunier "CNC" tapping head, that has clutches and
>gears to drive the tap forward when down feed pressure is applied,
>and reverses the tap at 2 X spindle speed when upward pressure
>is applied. The spindle of the CNC machine controls depth.
>I use Alum-Tap when tapping in aluminum, it works amazingly
>well.

Jon,

This sounds like a wonderful capability. I have some projects coming up
where that capability would be a huge help. However I get nervous
speculating on what happens if there is a mismatch between feed rate and
rpm? I don't have a good accurate way to set spindle rpm - although I
could probably adapt one of Sphero's digital tachs to my spindle some
way if I had to. The mill spindle has a variable speed pulley with hand
crank, and to complicate things (add uncertainty) it is fed from a VFD,
and the speed has to be manually adjusted each time it is turned on -
the Anilam control I have doesn't have a spindle on-off output, not even
a contact closure other than from the big red panic button (darn it).

I can do the basic arithmetic to calculate what tap rpm and feed rates
would go together, and what the hole depth would be, etc., that's not
the issue.

My concern is for the following situations when using a tapping
attachment like you listed on The Animal:

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