Doug,
I'm in agreement with you on the size of the machine, but I differ in the type of guides for the axes. I think that linear bearings on all axes is a better choice. Also, for the gantry style routers, I believe two motors (one at each gantry leg) is probably the best solution, a single, central, drive would require that the entire bed of the machine would be moving, which adds more complexity than the two motor solution.
I've never cared for rack & pinion systems, they invariably have backlash that affects the accuracy & repeatability of the machine.
I really like the looks of this piece of equipment:
www.probotix.com/CNC-ROUTERS/COMET-CNC-ROUTER
, although I'm a little apprehensive about the acme drive screws. A design like this, with the ball screws replacing the acme screws, would be my idea of an ideal solution.
I am afraid that I've made an expensive mistake in purchasing my 840. I have yet to get the machine operating correctly, and I have fears that I may never do so. It's not that I am without knowledge or talent, I have been a professional CNC programmer, operating & working (including complex repairs and retrofits) on CNC equipment for over 15 years.
The machines construction, as you point out is less than optimal. On top of that, since I now am aware of it's deficient nature, I cannot, in good conscience,bring myself to sell it to someone else. And I can't find any info on Stepcraft's site about return policy, I've sent them an email, so we'll see. I blame myself for not doing sufficient research, of this forum and other reviews, before I purchased the machine. We live and learn, however, this looks to be an expensive lesson.