Best belt drive ever! (If I do say so myself) - CNCzone.com-The Largest Machinist Community on the net!
I've built a prototype with a stepper (haven't tried it yet), and someone else has one working. You're tank tread idea is discussed there as well.
Try Modern Linear or Superior Bearing. Don't be surprised if the shipping is $20 or more, so order everything at once.3) Speaking of those grooved bearings...
I started off looking at ideas with the skate bearings and angle iron, then grooved bearings and the thin edge of angle iron, CRP's guides, and so on, but I think I really like the grooved bearings and the actual rails they are DESIGNED to roll on. Can anyone point me at the best price/source? I get a bit annoyed at looking at catalogs with no prices in them. Makes it hard to budget.
4) Router-mount overhang.
One of the earliest sites I visited was cncroutersource.com, which had a lot of really good information, but alas has a LOT of incomplete pages. But one that was there discussed moment arms in your typical machine. Since I've been planning to build the machine from wood, primarily Russian Birch Ply, I was very concerned with rigidity. I could see LONG moment arms caused by both the router hanging way out there at the end of an L-shaped Z-axis carrier, suspended under a very high Y-axis in the vertical plane.
I wanted to counter this by first, making the "wheelbase" of the x-axis carriage very long (almost 2' in some variants I've been contemplating), and second by having the Y-axis be in a horizontal plane, with the Z-axis carrier being between the rails. it would REALLY shorten up that moment arm.
But I can see some big problems with this approach, including that I'd basically be making TWO y-axis gantries to support a box in the middle, doubling my weight and the number of bearings and length of rail. I've considered making what I was calling the "front rail" considerably less substantial, using it to counter twisting moment, but not really carrying a lot of weight.
The primary mission of this machine is cutting shapes out of plywood, so the clearance will stay pretty low, also shortening the moment arm. But am I obsessing unnecessarily?
I've got a pretty compact design made from baltic birch ply.
http://www.cnczone.com/forums/1073084-post3.html (Z AXIS - Moving bearings or moving rails ?)
But both the Shopbot and Mechmate use the double gantry approach, with the spindle in the middle.
5) And on the topic of the Y-axis...
Triangular torsion boxes. Not much to say there, but that's what I'm picturing. A vertical member for the rails to be attached to, a horizontal member for rigidity, a bunch of triangular webs, and another piece of wood closing up the back.[quote/]
Harder to build, harder to mount??