Re: [CAD_CAM_EDM_DRO] Rigid Tapping--How is this accomplished?

On Mon, 2003-10-20 at 11:50, Jon Elson wrote:

> >
> I don't understand the problem here. Generally, the spindle rotation
> cannot change
> very rapidly, due to motor inertia. On most commercial machines, the Z
> axis linear movement can accelerate many times faster than the spindle can
> change speed. Remember, on a 40 TPI tap, the Z axis only needs to move one
> inch for every 40 spindle revolutions.

The problem might lie in the Z axis synchronized feed command. It needs
to keep feeding even while the spindle is slowing down to a stop. You
can't end the feed command and then turn off the spindle. You need to
turn off the spindle and then end the speed command.

Those of us that have the source code to our CNC control software can do
this if our programs don't already do this.

> I use a CNC
> tapping head,
> which handles the reversing of the spindle when the quill feed reverses, but
> the tap doesn't know the difference. I have tapped several hundred 6-32
> and
> 10-32 holes in minutes with these taps. the tap is just run all the way
> in in one
> pass, then brought back out.

Please tell me more about your tapping head. Who made it, etc. How do
you feed the CNC machine, just a synchronized Z axis movement or does it
even matter ? Would you prefer rigid tapping (compression/extension) or
using the tap head ?

> I got a single ROW thread milling tool, for about $45. It will do
> 1nything above
> 1/4" major diameter. It has 4 teeth with an OD of 1/4". I have milled some
> oddball threads in aluminum and aluminum bronze, and they looked BETTER
> than tapped threads! it is not as fast as tapping, but for special
> threads, and
> where it is not practical to mount the part on a lathe for single-point
> threading,
> it is a great thing.

What does ROW mean ?

Those mills are pitch specific, right ? Yours can't do any thread above
1/4", can it ?

I'd love to have *ONE* tool be able to do all our threading for all
holes above 1/4".... that would be heaven !

> I have a program that writes the G-code for this. See near the bottom of
> the page at http://jelinux.pico-systems.com/gcode.html
> I really need to put taper in so you can do pipe threads, too.

The source code for TCNC is pretty easy to work with. I've implemented
a bunch of "Kim Special" canned cycles: G770, 771, 772, 773, G102, G103,
G122, etc.

> I have a PRocunier model 15000 "CNC" tapping head. It has no overload
> clutch, otherwise it is similar to the non-CNC units that don't have a
> leadscrew.
> You program in the spindle RPM and dividing by the thread pitch gives
> the Z feedrate. Retraction is at twice the forward feedrate on most models.
> I have used it with no trouble, as long as I didn't ram the tap all the way
> to the bottom of a blind hole. I have a program to write the G code for
> this, too.

I was looking at those. The price seems right. Thank you for sharing.

> --
> Kim Lux <lux@...>