The main purpose for doing this was to allow the entire idler to rotate with the belt, removing the possibility of friction at the top and bottom.
The attached file is the STL for R4A-2RS bearing idler slip on.
This is a deritive of the work in the following thingiverse http://www.thingiverse.com/thing:16627
I downloaded the OpenSCAD file and modified the values to give me a slip on idler for the R4A-2RS bearing.
The values at the top of the SCAD file allow for modifications for just about any type of pulley or idler.
I found that printing 2 or more at a time allows the layers to cool down properly and allows the teeth to hold their shape.
Also, you will need the original bolt and lock-nut. I use two #10 washers below the bearing to raise it off of the plastic and one above for the bolt. The cover is press-fit, it is meant to be a tight fit so as not to slip off during use. I use ABS to print this, I modified the values to compensate for shrinkage of the ABS.
For the H-1, I plan on replacing three X axis idlers and 2 Y axis idlers.
