Abstract: A belt grinder includes a base plate mounting a drive motor, belt drive wheel, and belt tensioning idler wheel. A tension arm movably mounted on the base plate is biased to an extended position under a predetermined adjustable bias force to regulate belt tension. Air cylinder and weighted pivot arm embodiments for biasing the tension arm are disclosed. The idler wheel is pivotally mounted on the tension arm for adjusting position of the belt along the axis of the idler wheel. A plurality of grooves in the base plate allow precise securement of various attachments in repeatable alignments. A platen assembly attachment includes a tool rest and belt platen disposed between belt supporting rollers which may be quickly removed from the base plate and reattached in precise alignment without disturbing the adjustment of the tool rest and platen.