Sometimes gravity & alignment aren't enough to keep the bridge from hanging-up on descent, these keep the Z-rod nuts in their wooden slots to make sure the bridge descends everytime, no surprises.
I made these to clip on the back of the bridge so they wouldn't detract from the beauty of the Printrbot. After printing, remove support scaffolding under top clips. Place into upper wooden slots first & press down, then slide their feet (keepers) onto the Z-rods and press flat.
The left side mounts inside the left tower, the right mounts on the back (remove long screw & nut to gain clearance, replace when done) see photos. You -do not- have to remove the pulley & belt.
Both pieces have a slight overhang, so don't forget to enable "support" or "scaffolding" when slicing & remove them after printing. Use a fill density of at least 50%.
- Thing name corrected: now "Z-nut" (thanks tschutter, long night)
- Z-nut Keeper L v2.stl uploaded: a) taller b) top clip no longer hits Z-rod (deleted v1)
- Added photo: Z-nut Keeper L v2 inside left tower
- Instructions improved slightly.