Some background: I found the carcass of an enormous cnc plasma table at my local scrapyard. The gantry was gone, as were all the electricals, motors, etc. But what was still there was the ball bearing slide (singular, I'll come back to that in a minute) and the gear racks that used to move the gantry.
I'd had a hankering to build a cnc plasma table myself, but this was waaay to big for my shop. So I got to thinking, I'll get the slide and the gear racks, cut the slide in half, then viola! I have two 6' slides for the y-axis of a cnc plasma table, and I'll keep my eyes peeled for suitable slides for an 8' travel x-axis, (worth noting here, I have shorter precision slides I'd salvaged off of other stuff for the z-axis) and bada bing bada boom, I'll have a chassis for a 4x8 plasma table!
Well, months turned into a year or so, and the parts are just taking up space in my shop, no suitable long ways have crossed my radar. And so I got restless, and got to thinking. The gear racks themselves are big chunky hunks of steel. They're about 1.5x2" in cross section. They also appear to be ground flat, square, and straight. They'd necessarily have to be or else the gear teeth cut into them would be garbage. So why not use them as rectangular ways? Also, they're really beefy, so why not use the machine as a cnc router too? Just interchange the heads.
I'm not after full machining center precision here, just perhaps .005/inch repeatability or better. Is there anything in particular about using rectangular ways on a machine like this? (The ones we use at work just end up needing gib screw adjustment from time to time.) Have any of you seen anything similar to this done? Any thoughts?
No reason it couldn't be done, if I'm understanding your description properly.
You might need to spend quite a bit of time designing some proper "carriages" to fit the "ways", and keep in mind Z-axis thrust (IE, can the carriage/gantry "lift off" the ways- don't count on just weight to hold it there) but as long as most of that is taken into consideration, it seems at first blush, viable.