Adjusting the Bell Everman Drive

The KL7 series CNC Routers from BobsCNC feature a Bell-Everman belt drive that virtually eliminates belt stretch and backlash on the X and Y axis.  The Bell-Everman drive system employs two belts, one static and the other, dynamic.  The static belt is permanently attached to the plywood rail with double-sided tape on the X and Y axes.  The teeth of the static belt act as a gear rack.  The teeth of the dynamic belt are looped from under idler pullies over the drive gear which is connected to a stepper motor. 

It’s very important to properly tension the dynamic belt making sure that the teeth and grooves of the upper belt are fully meshed with the corresponding teeth and grooves of the static belt. Over tightening the dynamic belt will pull the teeth and grooves out of mesh from the static belt. This results in visible gaps in the mesh.  This will shorten belt life and adversely affect machine performance.