Almost ultimate Y-axis belt tensioner

I really like the simple and function design of the original G.design model. However, it carries over two flaws of the original Prusa's design:

• A lack of adjustability along the X-axis necessary to align and reduce the sideways pressure on the belt.
• The 623h bearing just flops on the bolt which result in the outer race of the bearing (sides of the pulley) rubbing against the sides of the plastic bracket. The inner race of the bearing normally utilized to mount bearings remains unused.

This remix attempts to solve these flaws by:

• Added 4mm of sideways travel to the mounting holes for the bracket to allow for side-to-side adjustability.
• Made a better use of the 623h bearing by making the opening in the sliding bracket 2.2mm wider and keeping the bearing centered by propping the inner race of the bearing on either side with two “sleeves” made from modified nylon lock nuts.

I also including a variant of the mounting bracket that has no lateral adjustment but still accepts the widened slider.

Compared to the original design, you would need these additional supplies:

• 2 nylon lock nuts. I have used these: https://www.amazon.com/gp/product/B075ZZW7VL/ The actual brand is not important, but make sure yours are 3.9mm high.
• M3x20mm bolt in place of the M3x18mm used in the original design.
• 1/8" drill bit. 3mm would probably work too, since M3 bolt is 2.9mm in diameter.

Instructions:

1. Drill out the center of each lock nut. The goal is to make the nut slide freely on a M3 bolt.
2. Put lock nuts into the inner race cavity on both sides of the pulley, making sure the round side of each lock nut is facing towards the pulley and the hex side is facing outside.
3. Holding this pulley “assembly” by the lock nuts, push it into the sliding bracket. Align the nuts and the pulley with the holes in the bracket by using an awl or a nail. NOTE: If you have your belt already adjusted for the G.design original bracket - make sure to put the belt on the pulley before you press it into the bracket.
4. Assemble the rest of the holder as in the original design. Tip: thread a temporary bolt into the nut on the back of the mount that is used for slider adjustments. This will keep it from falling out while you are working on bolting the mount to the frame.
5. Use the embossed center line on the mount to align it with the mounting bolts. This would be its factory location. Leave the mount bolts a bit loose so that you can still slide the mount side to side.
6. Tension the belt as described in the G.design's original page.
7. With the printer off, slide the bed back and forth and see where the belt is resting on the pulley. 
8. Push the mount a bit towards the side that rests the belt. Slide the bed back and forth a again. 
9. Repeat step 8 until you find a spot where the belt jumps to the other side of the pulley. This would be your location of the least side pressure on the belt. Although it is mostly impossible to make the belt stay in the center of the pulley (this would require a concave surface on the cylinder that rests the belt), you should be able to shift the belt to either side of the pulley, slide the bed back and forth, and observe the belt staying on the same side of the pulley.
10. Tighten the two mount bolts.

I think this can be further improved by using an adjustment screw for side-to-side adjustments, much like you do in belt senders. Still, the current design should be fine for rare adjustments.