An underpinning machine includes a worktable (11) having a central recess (17) housing one or a pair of underpinning heads (20,21; 120). The or each head has a magazine (18,19) of V-nails or wedges associated with it. In a single head version, the underpinning head (120) is power driven between two stop positions and is capable of operation by a drive plate (27) power operated (28,29) from spaced pneumatic rams disposed below the worktable. In another embodiment, two underpinning heads (20,21) are both selectively positionable within the area of the drive plate (27). The operation of the drive plate therefore automatically operates the underpinning heads whatever their position relative to fixed guides (31,32) of the apparatus which locate framing members (42) to be underpinned. By having the underpinning head indirectly actuated by the drive plate (27), a compact and flexible apparatus is provided and in the twin head version the underpinning heads can be placed very close together since there is no interference between respective drive mechanisms.

A clamping head assembly for clamping frame members in an underpinning machine includes a pair of clamping members each of which has upper and lower elements spring biased apart. The lower element carries a friction pad and is connected by a pin and slot connection or a parallelogram linkage to the upper element. Downward pressure on the clamping members causes slight longitudinal movement of the friction pad tending to pinch together the frame members at a mitre joint where they are held, for example, for underpinning.