I waffled on openbuilds gantry sets vs. linear rail for X and Y.
I just ordered 1440mm long X rail with short (C) carriages, and 2 850mm long Y rails with long (H) carriages. I went with MGN12 to be wide enough to attach over T/V slots, but saw no reason for wider and thus heavier MGN15 or MGN20. I went for H carriages on Y for additional resistance to tangential racking forces to avoid potential binding from the overconstraint. (I’m also thinking about using a custom 3d printed plate to attach the Y carriages to the X rail in order to bend instead of bind if anything goes wrong.)
No, I didn’t buy real hiwin. Not for 1440 X and 2 850 Y rails. But if they are loose, I don’t think that I’m going to notice the lack of precision relative to the width of the laser beam; if the bearings are tight, I’ve successfully stoned the grooves in MGN rail to run smooth after replacing bearings and discovering that the new bearings were a little larger than the previous ones. Also, if they run rough, I can stone out imperfections. So right now I’m betting on “good enough is good enough.”
For reference, from banggood, MGN12-1C-1440 was $50, and MGN12-1H-850 were $40 each, plus $36 to ship the three. $166 total.
I’ll find out in a few weeks, I suppose. 