I'm not trying to suggest that Stepcraft completely overhaul their basic design here , I was just wondering what users consider to be the ideal solution for engaging the moving assemblies with the tracks on a theoretical CNC machine. Stepcraft's brass roller solution doesn't seem to be optimal either for a self-assembly CNC machine kit or a turnkey solution.
I.e., if you were to design your own 'ideal' CNC machine, what solution would you choose? My ideal machine configuration would not have a larger XY footprint than the 2/840 machine I already have. Myabe a little more Z axis travel would be useful, but I don't need much for milling guitar bodies, necks and other 2.5D parts from plastic or aluminium.
For the Y axis in particular, I was thinking of a central ball screw/ball nut for the linear drive mechanism coupled to one powerful NEMA stepper motor (at least a NEMA 23) with a rack and pinion either side and a locating bearing with some built in float at the opposite end. The ball nut would be mounted at the centre of a rigid axle, probably within a housing with aluminium tube sections either side would suffice to keep the weight down.
Would this be subject to alignment challenges do you think? I guess it depends on the rigidity of the transverse axle and amount of pinion tooth engaged with the track.
I see from a quick Google search that the EZ-Mini from EZ-Router.com operates with a rack and pinion drive on both X and Y axes:
Has anybody else designed and/or build their own CNC machine? Possibly not the best forum to be expressing these ideas or asking these questions on is it? I guess
is better but I'm not about to join yet more forums right now, my digital footprint is already far too large.
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:
, 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.