Re: Re: Electronic Lead Screw & Power Cross Feed | Poor Man''s CNC ?

I didn't realize this is such a big thing. Reason I say that is I
added "ratio" to to the G-Rex instruction set but thinking it would
be a semi-useless instruction.

Ratio (RTO) causes an axis to select a target and follow it at a
fixed ratio. It works like this:

Say you have a 500-line encoder on your spindle and you have a 10-
microstep drive. The spindle will genererate 2,000 counts per
revolution and the drive will move at 2,000 steps per rev. Both are
equal.

Let's also say you want the step motor to move at 1/10 the spindle
speed. The step motor is in the x-axis group as is the encoder. You
would send the following insruction to the G-Rex:

RTOxENCx+1000000000<cr>

Meaning "have the x-axis motor track the target ENCoder x at a ratio
of 0.1000000000 of the target's speed." The step motor would follow
the spindle speed (position) in the same direction to a 10-place
accuracy. That should be good enough for most folks.

That's all there is to it. Connect a laptop to the G-Rex via USB,
download that line of code from NotePad, disconnect and walk away.

Mariss

--- In CAD_CAM_EDM_DRO@yahoogroups.com, Jon Elson <elson@p...> wrote:
>
> John Stevenson wrote:
>
> >>Vaso wrote:
> >>
> >>
> >>
> >>>Bob:
> >>>
> >>>You've done an excellent review of the entire issue. Full CNC is
> >>>clearly far more complex than electronic lead screw - and
requires far
> >>>more learning time. CNC leads to a different lathe machine
altogether
> >>>- where "machining" is replaced by "programming" - even for
simple
> >>>one-off pieces. I understand - once converted to CNC - a "CNC
lathe"
> >>>cannot be a good "hands-on" manual lathe - except maybe with
expensive
> >>>electronic handwheels.
> >>>
> >>>
> >>>
> >>>
> >>Not necessarily true. We have a Bridgeport/Romi CNC lathe at work
that
> >>can be used manually as if it only had a DRO. You might notice a
slight
> >>drag on the handwheels, that is about the only sign. I don't see
why a
> >>CNC setup that preserved the handwheels couldn't be used manually.
> >>It would need either low-cog stepper motors or servos. If the
servos
> >>had feedback to the computer, then it could act as a DRO when not
in
> >>CNC mode.
> >>
> >>Jon
> >>
> >>
> >
> >Mach3 does just this. A seamless swap over from manaul to CNC with
the displays acting as DRO's
> >
> >
> With a number of limitations. For instance, the encoders can never
> exceed about
> 30,000 counts a second or there is the possibility of lost counts,
since
> this is
> a software-only encoder counter. And, of course, you need to have
encoders
> and servo motors to read the position at all.
>
> Jon
>