There's an infinite ways to design a machine, so I'm gonna just skip that part. I'm building on the fly with what ever I can find at he hardware store and a couple other places in the neighborhood. This my first machine, I have no real use for it, just for fun.
Its all MDF, and the only tools I have that cut reliable square are a router table and a drill press. So my bearing design is based on that. I got skate bearings that were on clearance at a sporting good store, $15. They are 7/8" dia. X 5/16" and a 5/16 bore, so I got 5/16 all thread for lead screws. I found steppers at a place called "American Science and Surplus" $.95 each. And finally a 3-axis board from Ebay for $60.
For the Y & Z-axis, I cut a chunk of wood that looked real good for the bridge and cut a 5/16" channel in each side. Then I used that with a couple bearins as a spacer against the fence of the drill press, drilled 2 holes in the Z-axis plate. Removed the bridge / bearing spacer stuff and drilled the other 2 holes. I cut a groove on the back and chiseled a little to fit the nut, and used a mending plate to hold it in. The X-axis will just be a board that rides on top of bearings, maybe a couple on top to hold it down. One pictue show the nut I found, its called a plug bolt and fits perfectly in a copper pipe hanger. But I'm not to that point yet, will get more indepth when I get there.
So, on to the pics
Interesting idea. The groove does make for a straight place for the bearing to ride on.
I have seen some metal tapes (copper, Al) that might be useful for reducing the wear in that groove.