Re: [CAD_CAM_EDM_DRO] USB and ncPOD system

At 10:41 24/05/2007, you wrote:

>Tony Jeffree wrote:
> > At 09:01 24/05/2007, you wrote:
> >> The ability to download gCode DIRECTLY
> >> to ncPod and run it from there may well provide a solution to the lathe
> >> problem since it would not require a return path to the host computer.
> >
> > That would only provide a solution if the ncPod firmware is able to
> > handle inputs from the encoder and modify its step rates accordingly.
> > If that was possible it would significantly increase the appeal of
> > the 'pod - right now I am looking for a solution to the lathe problem
> > for my ongoing of Myford conversion.
>
>Since this relates to ELS and a few other areas as well, I'll ask
>the questions :)
>The problem we are trying to solve is locking the movement of the
>tools to the
>rotation of the spindle?

Exactly that. Without that capability, yes you can run a lathe for
plain turning applications, but IMHO a CNC lathe that can't thread is
not a lot of use.

>The ideal solution would be a spindle that has a positional drive, with a big
>stepper or servo, but since that is not going to happen, we need an
>encoder on
>the spindle that gives the position information.
>
>There seems to have been agreement that a single pulse is all that is needed
>so you know when the spindle has done one rotation, but in that case the tool
>may need to accelerate or decelerate if the spindle speed has changed?

That is (as I understand it, anyway) essentially what Mach and other
packages such as Turbo CNC do to implement threading for lathe
operation. In Mach's case, it can accept multiple pulses per rev plus
an indexing pulse (the latter being a longer pulse rather than a
separate signal).

>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.

Yes, my thinking was going in that direction too as a basis for
converting my Divisionmaster software into an electronic gearbox.
Haven't got further than convincing myself that it is possible so far.

Clearly, the ncPod also has the potential to do some/all of this
on-board given the right firmware. Going any other route (feeding the
encoder back to the PC etc) seems to be a non-starter due to the time
delays imposed by USB communication.

>Am I missing something?

Just missing the right firmware as far as I can tell ;-)

Regards,
Tony