Re: [CAD_CAM_EDM_DRO] Re: Tapered Threads? Kim's TurboCNC codes

On Mon, 2003-11-03 at 10:59, Jon Elson wrote:

> >Multiple encoder counts are pretty much unnecessary. I've cut threads
> >with TCNC that got 10 or more passes and they came out beautifully
> >clean.
> >
> >
> >
> Yes, for lathe threading, this is probably good enough for most work.
> But, for the very similar rigid tapping on a mill, it is not good enough,
> because the spindle must stop and reverse while the Z axis follows the
> spindle rotation precisely.

Almost no mill follows the spindle well enough to do without a
compression/tension tap holder. Some claim to, but almost everyone uses
a T/C tapholder. With a tension/compression tap holder, once per rev is
plenty good enough. I'll be purchasing a tc tapholder soon and
testing/proving this.

> When the spindle shuts off and reverses,
> the speed change per revolution can be very large, and the once-per-rev
> pulse will not allow the Z axis to stay in close enough sync.

It takes TCNC a couple revolutions to sync. With T/C tapholder this
will work fine. Most T/C tapholders have +/- 1/2" of travel. At any
reasonable thread pitch that is quite a few spindle revs.

Furthermore, if TCNC needs multiple pulses per rev, I'll add it... The
syncing part of the TCNC code is pretty simple.

> The other place where a single pulse/rev may fall down is in multi-start
> threads. Theoretically, you can still do multi-start threads with a single
> pulse, however. I don't know if TCNC supports that.

To do a multi start thread with a single pulse per rev, simply start the
Z axis at a different spot. Ie lets say we are cutting a double start
10 TPI thread. I'd cut the first one starting at Z=0. The second
starting thread would be started at z+ pitch/2 = z+0.050".

I can do double start thread milling as well, the same way, by
offsetting the Z axis the appropriate amount.

Kim

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