Re: servo mill for possible conversion

> > From: "David M. Munro" <munro@...>
> > Here is a mill on eBay, for a possible PC control conversion. It is
> > located in Ark. and looks to be in really clean condition. Any thoughts?
> > Is this a project you'd like to take on? Is this a decent quality

machine

> > worth pouring some money into?
> >
> > http://cgi.ebay.com/aw-cgi/eBayISAPI.dll?ViewItem&item=202770474

> From: Jon Elson <jmelson@...>
> I couldn't tell how big this machine is. It most likely has DC servo
> motors, but may have resolvers instead of shaft encoders. These will
> require a converter/interpolator, or need to be changed to encoders.
> Servo amps may need to be changed. The CNC control has got to
> be one of the oldest I've seen, must be mid 60's.
>
> Note, this is a 2-axis CNC. The quill feed is air operated.

My comments are:

1. What Jon said.
2. In its current condition, especially if it still works, it's a real museum
piece. It would almost be morally wrong to alter it.
3. Notwithstanding #2 above, there are a few practical considerations:
a. X & Y may be stepper actuated, not servo. Jon is right, this is really
old, so that's possible.
b. I wonder how much backlash there is in the quill drive mechanism.

Conclusion:

The machine is apparently in great mechanical shape, and the price ($850 last
time I looked) is low, but if you buy it the only thing you can count on
getting is an X & Y ballscrew equipped knee mill in good condition. If you
can reuse any of the electronics or motors then you can take that as a bonus.
Excello is a good brand so that counts for something as well.

The machine I recently retrofitted (that you saw at my shop) is tentatively
sold and should be leaving within a week or two, so I have the room for
another project. If you do buy that machine I could certainly do the retrofit
job. My main reservation is what to do with the quill drive if the existing
arrangement isn't satisfactory. From what I can see in the pictures, they
have replaced the manual quill feed handle on the right side of the quill
housing with a purpose built rotary actuator. Downward motion is limited by
the stop rod assembly on the front of the quill housing. Unless they have
found a way to eliminate the backlash in the quill drive rack it's likely
we'd have to scrap that whole contraption in favor of something like what Jon
built for his Bridgeport Z axis:

http://artsci.wustl.edu/~jmelson/CNCconv.html

(look near the bottom of the page)

Another possibility is to have a 2-1/2 axis machine by controlling the X & Y
and living with a Z axis that is either "up" or "down" like a pen plotter or
signboard cutter (you probably don't want this...). Let me know what you
think and I'll keep looking around as well.

Matt