Disclaimer

I never built this and I designed this years ago. It might be possible to tap the adjustment screw hole, but I don’t know. Just use belts and don’t worry about tensioning. Nevertheless, here is the idea.

CAD

Download on GrabCAD here

Note: The bearing diameter and adjustment travel are set as global variables and other dimensions dynamically scale based on those values.

Construction

1. Mill the outer plates and sliding bearing block Note: Make sure the distance between the “rails” of the outer plates is slightly more than the thickness of the sliding block
2. Clamp the outer plates together using the four mounting screws
3. Drill and tap the hole for adjustment screw
4. Assemble as shown
5. Tighten the jam nut so the adjustment screw is retained

Adjustment

1. Loosen the jam nut
2. Turn adjustment screw to slide the bearing block
3. Tighten jam nut to prevent motion