Re: [CAD_CAM_EDM_DRO] Re: Threading on a lathe with EMC

> I don't see the difference. A VFD used in a loop would be the same as a
> servo motor. The computer only outputs a voltage to control torque and
> reads position and speed. If EMC was told the acceleration of the
> spindle "servo" was very slow EMC would not try to change it's speed
> more rapidly than it could respond. EMC would then adjust the carriage X
> axis to match the spindle position which it has some but little control
> over.
>
> Could EMC handle such an axis? The speed would be very fast but the
> acceleration of it very slow. It would kill the idea if EMC had to stop
> spindle motion between each move but I understand it does continuous
> contouring.
>
> What am I missing. :-) Thanks.

Please put this VFD and encoder in a box, ship it to me, and I'll be glad
to tell you ;-)

Seriously, it may work. There are drives that can do a nice job of
servoing and A/C induction motor for accurate positioning. But I'm
not sure you will get satisfactory performance from a common VFD which
probably has a fairly low bandwidth. (It's sort of like when I
proposed using a 1hp DC motor as a servo... I may still do it, but was
warned not to expect high performance)

However, it's fairly easy to try it if you have the VFD on hand and
the necessary I/O in the computer. Rig up an encoder, even a
temporary one, and set up the VFD as say the "Y" axis which wouldn't
be used in EMC lathe mode anyway. Then simply program 'diagonal'
moves in Y and Z where the 'slope' is determined by the thread pitch.
These will probably begin and end from a dead stop, but you could also
try it with some preceding and following moves on the spindle "Y" axis
alone.

If you can get it to work as G-code, then it should be possible to
modify the command interpreter to make it work like a threading cycle.

Chris