Alright then; I'm free to ramble on here a bit.
Stated before, I like the current wheel on extrusion linear setups available, yet there is a lot that I don't like about building machines with it exclusively.
1 - Nylon and polycarbonates are decent economical choices for wheels on lightweight builds that exert very little force [engravers, 3D printers, laser/plasma cutters]. Larger/heavier mill builds can deform or crack those materials sooner than later when put to task on regular, high force machining. Also any direct steel wheel contact would gall the anodized aluminum surfaces quick fast and in a hurry.
2 - The sections of alum extrusions used for linear motion are too thin and unsupported. These channels can warp and deform with prolonged high force use rendering accuracy null. Plus depending on where the framing comes from to start with, manufactured/delivered quality and consistency can be largely hit or miss. You really have to QA every inch of any new stock.
3 - Less complaint and more "wish they would have"; I appreciate the specifically designed extrusions for this application but really would have liked to see a better wheel system developed for existing products too.
4 - The preferred use of "20 series extrusions" is way too small for realistic goals. Within that dimension all compact wheel designs are confined to using std/deep groove radial bearings only. A larger framing series could facilitate a larger wheel that would use a matched set of angular contact bearings to better address the dynamic loads of a CNC linear system.
5 - Quarter inch thick alum plating for body parts still lacks significant anti-deflection characteristics under high cycle loads. Add to that relying on the use of spacer bushings to account for frame depths in build up is a potential weakness.
These are my top 5 gripes, and things I've been working on in house for a few years. It would be great to hear any other complaints and imagined solutions about this from y'all. At the same time I aim to keep this topic friendly and not solicit anything in anyway.
*Admin", please pigeon hole this thread as needed. I'm certain to have missed a posting rule or two.
MC