A portable slitter for selectively roll slitting rib forming or perforating sheet metal workpieces and having a beam-type frame, a pair of spaced thin walled and light weight rotary torque tube roll shafts mounted in the frame and supporting the work rolls, and a plurality of pairs of opposed stabilizing support blocks disposed between the shafts and the associated frame beams and providing further strength to the shafts by functioning as intermediate span shaft journal supports carrying the roll work loads imposed on shafts directly into the frame beams. The bearing members can be readily removed and adjusted longitudinally of the shafts without taking the frame apart. The slitter can be readily manually transported to the work site because it has a high strength-to-weight ratio and is light in overall weight. The slitter has substantial operational strength and improved work roll registry and alignment under continuous and/or adverse on-site operating conditions.