Xzero Raptor CNC build - linear rail and ballscrew selection

[Mattia]

Thanks all! I've dry-assembled the Z axis, didn't get around to the other two just yet. Looking and feeling good so far. I've been dabbling with Fusion360 (not quite 'got' it yet, but working on it) trying to come up with a design for mounting a pair of 200w servos for the x axis (on the assumption that two 400w servos for a gantry this size would be rather overkill).

What I'm considering is mounting two 2020 ball screws inside the frame alongside the extrusion, face mounted to the end frame pieces using FK/FF mounts, having the lock nut on the fixed end recessed into the frame. Then mount a 40 tooth HTD5 pulley on the ballscrew. The idea is to find someone who can machine the end frame for a recessed 60mm motor mount with elongated bolt holes to allow for tensioning the 20 tooth pulley on the motor.




The way I've sketched it now leaves 7mm thickness for the motor bolts, with a 3.5mm recess for the round flange surrounding the motor's shaft. I'm guessing I should oversize the slots and recesses somewhat since it doesn't need to press fit in place and I'm not sure how tight the tolerances on the average 60mm frame motor are (0.5mm per side, or total? Suggestions welcome). Will this leave enough meat for the motor? Would 5mm be enough as well? How long would you leave the slots for belt tensioning? I've gone with 6mm slots for M5 bolts that are 16mm long. Too much? I'm a little concerned about the clearance at the edge of the hole to the recess for the plate around the shaft. Also need to work out exact positioning for this so the belt preferably does not run across the bolt caps, though an offset mount would mean less leeway in terms of taking up belt slack. Comments on this plan welcome. I'm also wondering whether to start a separate build thread or just keep all the questions here - I'm finding the dialogue very helpful in making decisions!