Abstract: The front idler roller of the belt sander is mounted by a yoke for swinging movement in a plane containing the axes of both the drive and idler rollers and for shifting movement along a path generally toward and away from the drive roller. A transversely disposed shaft mounted by the tool housing has a cam formation at one end thereof received within an opening formed in the yoke; the cam is captured in this opening formed in part by a cam follower. The shaft is mounted for axial and rotational movements. Rotation of a first knob on the other end of the shaft causes the latter to move axially thereby to swing the idler roller for centering of the belt. Rotation of a second knob, concentric with the first knob and also mounted on other other end of the shaft, causes the shaft to rotate thereby activating the cam for shifting the idler roller toward the rear roller for easy belt replacement.