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.
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.
- 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
- Clamp the outer plates together using the four mounting screws
- Drill and tap the hole for adjustment screw
- Assemble as shown
- Tighten the jam nut so the adjustment screw is retained
- Loosen the jam nut
- Turn adjustment screw to slide the bearing block
- Tighten jam nut to prevent motion