I'm building my own printer design, and when it came time for the hotend carriage, I couldn't find anything on Thingiverse that would work with my design, and I didn't want to redesign the whole thing, so I opened up Inventor and whipped this up. It's a symmetrical design, so print two and bolt them together. As designed, it's intended to run along two horizontally-oriented 8mm steel rods using linear bearings, spaced 40mm apart. You'll need to ream out the bearing holes for a proper press fit. I'd use a 37/64" bit on a drill press, but you do you. It also has a 40mm fan mount for part cooling. I'll update this post with refined designs as I manage to model them, and pictures once everything is printed and assembled.

Monoprice Select Mini

No

Yes

0.1mm

50%

Hatchbox PETG:

245 C extruder
70 C bed

I designed the bearing holes to print undersized, with the intention of reaming them out with a drill press for press-fitting the bearings in. The design is symmetric, so print two and bolt them together. The bolts I use to clamp the halves together are 75mm M6 bolts with nuts and washers.