Re: [CAD_CAM_EDM_DRO] USB and ncPOD system

At 05:41 AM 5/24/2007, you wrote:

>Multiple pluses from the spindle along with an index pulse could be more
>useful, as long as the firmware knows what to do with it? My own thinking has
>been that a high speed, high res encoder on the spindle would generate a
>reference pulse train, and the drive to the tool paths would basically divide
>that down and so keep everything locked so that you could turn the spindle by
>hand and the tool would move - back and forth in sync? An electronic version
>of the gearbox on the lathe, except you can change the gear ratio
>depending on
>how far you are along the job.
>
>Am I missing something?

Nope, what you need is a rotary encoder with an index
pulse. Generally something in the 200-254 PPR range is sufficient
with 254 PPR for a metric thread on an English machine.

Your hardware will probably do 4X count multiplication and your
software will probably need to do corrections on the fly (at 800 PPR
and 10 TPI on a lead screw, corrections roughly every 64 steps for
metric screw threads, unless I am mistaken.) Why the index
pulse? Ever cut a thread in more than one pass? Index pulses on
both the lead screws and the spindle make it easier.


David G. LeVine
Nashua, NH 03060