Re: [CAD_CAM_EDM_DRO] Building a small 4th axis

At 11:15 04/06/2003 -0700, you wrote:

>Not exactly the same thread, but I like these "symbiotic" ideas! A few
>days ago I saw a Sherline rotary table w/stepper being used to drive the
>Sherline spindle on a lathe for threading (and what not). Probably on
>Bryan's web site. Seems to me that a gearhead stepper motor (some
>Vextra's I picked up come to mind) could be used quite easily the same
>way. This would allow any CNC controller program to turn the spindle in
>direct ratio to the lead screw, which is what's wanted. The other way
>is to add an encoder to the spindle, "Sync" and drive a leadscrew off of
>that via software.

Hi Alan -

There was a series of articles a few years back in Model Engineers'
Workshop magazine, describing a CNC-ed Taig lathe. The guy had indeed
managed to do threading by stepper-driving the headstock via a reduction
drive, and driving the saddle traverse & headstock motors at appropriate
rates to generate the right lead per rev. Problem he described was that,
because the power available from the stepper on the headstock was
significantly lower than a conventional spindle motor, he had to use low
speeds (to maximise the stepper torque) & hence cutting any significant
thread length was interminably slow. Perfectly possible though.

I have done a similar thing on my mill - using a rotary axis to rotatre the
part to be threaded, and a 60-degree V-tip engravibg cutter to cut the
threads. See the second-from-last photo on this page:

http://www.jeffree.co.uk/Pages/divheadmk2.html

Took a while, but generated a great thread!


Regards,
Tony