These carriages work for 2020 aluminum extrusions and 15mm diameter V-wheels, such as the ones from OpenBuilds or RobotDigg.com.
A horizontal M3x35 screw is used for preloading the tension on the wheels.
You can get the ball studs from me for $1 each, and I also precisely build the carbon fiber, zero-backlash, magnetic arms. My website is http://www.MagBallArms.com
This design works nicely with my effector which sports an LED light ring and 3 PLA cooling fans: http://www.thingiverse.com/thing:1546124
Here are links to the mini V-wheels from RobotDigg:
Here are links to the mini V-wheels from OpenBuilds:
Per carriage, you will need:
3 of the above V-wheels.
3 M5x25 bolts.
3 M5 nylock nuts to secure the three axles.
2 3/8" ball studs (from me).
2 M3 nylock nuts to secure the ball studs.
2 M3x35 SHCS for the belt tightener.
2 M3 nuts for the belt tightener.
1 M3x35 SHCS for preloading the carriage wheels.
1 M3 nylock nut for preloading the carriage wheels.
1 M3x20 SHCS for the vertical post for the upper G2 belt attachment.
1 M3 nut to secure the vertical post.
1 M3x10 SHCS to secure the lower belt loop.
1 M3 nut to secure the lower belt loop.
You can easily alter the OpenSCAD source to make this work with 2040 or 2060 extrusions, by changing the value for extrusionWidth from 20.0mm to 40.0 or 60.0mm.
If your belts are farther above your carriages, you can easily adapt by using a longer M3 vertical screw.
The belt tightener this uses is very simple and easy to adjust with two M3x35 screws.
I found that this delivered better results than using zip ties. My prints got more accurate by about 50 microns.
I also have a version for 24mm diameter V-wheels: http://www.thingiverse.com/thing:2183347
Note: there needs to be a tiny shim between the aluminum spacers and the mini V-wheels, otherwise the aluminum spacers rub against the bearings.
I've design and tested carriages using both 15mm mini V-wheels and 24mm V-wheels, and I prefer the 24mm versions. Bigger wheels roll better and the shims aren't needed.