Just beginning my first build from Brian’s plans … everything swinging along great until I got to the part where the gantry gets mounted to the base. It would not fit …waaaaay too tight …couldn’t begin to get the linear bearings in place on the angle tracks. Hair-tearing time … went back, triple checked all measurements, dimensions …everything checked out down to the micron (well – maybe not microns, but you get what I mean). Completely disassembled everything, yadda-yadda … no joy. I had done everything right, but it didn’t fit. To shorten this sad tale – I finally realized the skateboard bearings I was using were 7/8″ in diameter, NOT the 5/8″ diameter ones specced in the plans. Sooooo …. bearings on each side 1/8″ too large (remember, the diameter was 1/4″ too large but the radius was only 1/8″ too large), means I had to find a quarter inch somewhere; decided to shave the linear bearing support rails down by an eighth and, mirabile dictu, everything fit like a silk glove. I guess the lesson is, if you’re working with tight tolerances (which a CNC build certainly calls for), even an eighth or two can make the difference between success and … notsomuch.
Now, on to the Z axis (remembering of course, that 7/8″ is definitely not the same as 5/8″.