A circular dovetail recess in the saddle receives a corresponding dovetail projection on the swivel head or swing frame, and the two are secured together at that point by a set-screw a. In addition to this the upper edge b of the saddle is an arc of a circle of which the centre is the centre of the dovetail groove, and a clamp is employed to fasten the swivel head to the saddle, being held to that head by a bolt, and therefore swinging with it. Thus the swivel head is secured to its saddle at its upper edge, as well as at its centre, which affords a better support.
The tool box is pivoted upon the vertical slider, and is secured in its adjusted position by the bolts n in [Fig. 1573], the object of swinging it being to enable the tool to be lifted on the back stroke and clear the cut, when cutting vertical faces, as was explained with reference to shaping machines.
Fig. 1583.
The tool apron is in American practice pivoted between two jaws, which prevent its motion sideways, and to prevent any play or lost motion that might arise from the wear of the taper pivoting pin b, in [Fig. 1583], the apron beds upon a bevel as at a, so that in falling to its seat it will be pulled down, taking up any lost motion upon b.
Fig. 1584.