A downhole rotary tool for comminuting tubing in a borehole comprises a tool body and a plurality of cutting assemblies projecting from or extensible from the tool body and distributed azimuthally around a longitudinal axis of the tool body. Each cutting assembly comprises a supporting structure and a plurality of cutters with cutting surfaces of hard material. The rotating tool is advanced into initial contact with the tubing to commence milling axially along the tubing and then advanced further to continue milling the tubing, At least one cutting assembly has material which is softer than the hard faces of the cutters and is positioned to contact the tubing at the initial contact and delay contact between at least one hard surfaced cutter and the tubing.