Re: CNC Router How-To's

In a message dated 99-05-10 02:17:47 EDT, Gar writes:

>> Yeah, and it's used on several largish gantry systems I've seen on the
>> Web. Me bein paranoid, I worry about losing a count, and racking the
>> gantry, rather than the racking forces of possible imbalance on the
>> guides. Guess we all have our boogie-men to deal with.

Encoders on the linear drivers?

Drive one end of the gantry with a linear driver riding on leadscrew and then
use a figure 8 loop of aircraft cable to drive the other end of the gantry.
With ball bearing pulleys and 3/16" cable tensioned to near its rated load
(300 lb-ish I think), this works pretty well. I've seen the cable loop trick
done on a torch cutting rig that was used to cut large shapes from steel
plate up to 6" thick.

>> Keep us posted; this sounds interesting for the "router-in-the-large".

After taking apart enough big dot matrix and impact printers for motors and
power supply parts it dawned on me that just maybe IBM engineers had a clue
about linear motion. Take the same concept and beef it up by a factor of ten
or even a hundred or so... hmm.. The cable translation scheme comes from
looking at some old HP plotters and doing the same kind of calculation.

I worked in the oilfield for a while and found that building things big is
often easier than building them small, if you know how to rig large
equipment. Up to a point, brute force is usually cheaper and easier to hack
than high tech.

Jon