Design critic needed for an 80/20 linear system

[userx]

I want to start by saying - Wahoo - my first post!

Now that that is out of the way I am interested in building my first CNC machine and I want to see what people think of my linear bearing design. Its based on a fiarly common practice of mounting bearings to an angle but a little more refined. I will use ground and pollished 1/2" steel mounted on 80/20 1530 extrusion through the bottom with 1/4-20 bolts (bolts not shown). As for my angle I will use 1/2" thick aluminum angle milled to shape and shoulder bolts retaining the bearings. The shoulders are recessed slightly into the angle to put the shoulder in shear under load. Anyway - I would have a set on top and bottom to capture the profile of the 8020/steel rail. What kind of accuracy do you think I can acheive with this type of system?

[LaserImage]

I would think that the portion of the 8020 that the rod sits on will flex enough to give you alignment problems. I would think that it would work better if you mounted the rod to a flat bar that sat on the 8020 instead. Or you could use something like the 3075 material that has a solid edge.

Gary

[Gary55Ford]

I have built X-Y tables out of 80/20 and used Thompson Bearing products, they have several rod configurations to choose from. I use thier linear bearings on the tables. I buy my parts from a co. called Linear Ind. in Monrovia Ca. they carry anything you may need for linear motion.

[solodex2151]

I would try using Ahren's linear bearing products. Specifically designed for 80/20 and not too expensive. However, if you want to roll your own, the main problem I see is the attachment of the angle and rail might be difficult. I agree with Gary on the 80/20 flexing a bit to much for your liking, but only on an unsupported span greater than 3'. Use their deflection calculator to see if your design can tolerate it.