Printed this out in PLA, 0.2 layer height, 20% infill, with supports on a QU-BD OneUP running at 30mm/s. Took around 8 hrs total, including the printed Nut and Bolt.
This X Gantry and Carriage is Awesome! I've been using it for about a month now, and it has eliminated all my gantry sag, given me more printable space, and just looks freaking awesome! Kudos to the designer, NoelJean (https://www.thingiverse.com/NoelJean/about) ! Thank you very much!! You can find their original design here : (https://www.thingiverse.com/thing:1503687)
On the rail slides, I used total of (4) LM8UU Linear Bearings, two for each side of the gantry. One goes in from the top, the other from the bottom. It is the same for both sides. I had to do some minor sanding, then I pressed fit them into place, securing them with a little ring of super glue around the outer rims. Worked like a charm!
The right side of the gantry, the bearing tension guide for the belt was a bit tight for my 608zz bearing, so I had to heat it up a little with a heat gun on low setting and widen the gap for the bearing. Easy remedy!
Even with the rods fully seated, my stock belt was to short. I remedied that simply by printing out the "XY_SlimCarriageV3" by NoelJean (https://www.thingiverse.com/thing:1503687/#files), but using the "simple_x-belt_clamp_V001" by markqv (https://www.thingiverse.com/thing:699109/#files) teeth configuration instead of the models original (the models original did not have the correct teeth for my belt). Even after that, I still had to cut my belt to give the extra length. There is plenty of belt left to hold it snugly, though. I thought I was going to have to glue the belt in place, or zip tie it down some way, but I haven't had to do any such thing. The belt has held secure even after 3 spools of filament, so I'm calling this a non-issue. :) Here is a link to my "QU-BD_OneUp_XYSlimCarriage(Stock_Belt_Mod)" (https://www.thingiverse.com/thing:1656310) This is the final model I'm currently using.
I printed out my own M10 bolt and nut using the "M10 Toolkit" by gringer (http://www.thingiverse.com/thing:1250982). I had to add a little blue painters tape to threads on the back of the bolt to help hold the nut secure. I fastened a rubber band around the bolt head, ran it around the gantry, finally looping the other end of the rubber band around the nut, just to help hold tension. This is probably not needed, but better safe than sorry, is my motto.
If you're interested in my setup....
I'm using the "QU-BD z access coupler" by gjacobs84 (http://www.thingiverse.com/thing:929476) to connect my Z axis.
The extruder I'm using, "WD Extruder for Qu-Bd OneUp TwoUp and others" by WorkerDrone (https://www.thingiverse.com/thing:858702) Printed in ABS.
Print the carriage on it's side.
Print the Gantry sides standing upright. You may want to flip the left side to use less support. You may be able to print this whole thing without supports, I didn't risk it.
Use circular printing for the M10 bolt and nut, if you choose to print them, no support is needed for the nut and bolt.