The base l of the chuck is bolted to the planer work table in the ordinary manner.
The work-holding frame or vice is supported, for circular surfaces, by being pivoted to the base at o, o, and by the gibbed head d, which has journal bearing at e. The work is held between the stationary jaw b or b′ (at option) and the movable jaw c which may face either b or b′ (by turning c round). Suppose then, that while the chuck is passing the cutting tool, end i of the work-holding frame is raised, lifting that end of the work above the horizontal level (the work-holding frame swinging at the other end on the pivots o, o), then the tool will obviously cut a convex surface. Or if end i of the work-holding frame be lowered while the cut is proceeding, the tool will cut a concave surface.
Fig. 1629.
Now end i is caused to rise or lower as follows:—The head d is adjusted by means of its gibs to be a sliding fit on the bar g in [Fig. 1629], which bar is rigidly fixed at p to the planer bed; hence as the planer table and the chuck traverse, d slides along bar g. If this bar is fixed at an angle to the length of the planer head, d must travel at that same angle, causing end i of the work-holding frame to rise or lower (from o, o, as a centre of motion) as it traverses according to the direction of motion of the planer table.
Suppose that in [Fig. 1629], the planer table is moving on the back or non-cutting stroke, then head d will be moving towards the point of suspension p of the bar g, and will therefore gradually lower as it proceeds, thus lowering end i of the work-holding frame and causing the curved link to pass beneath the tool with a curved motion or suppose the table to be on its cutting traverse, then head d will be raised as the table moves and the cut proceeds, and the surface cut by the tool will be concave.
Now, suppose that the bar g were fixed at an angle, with its end, that is towards the back end of the planer, inclined towards the table instead of away from it as in [Fig. 1629], and then on the cutting traverse head d would cause end i ([Fig. 1628]) of the work-holding vice or frame to lower as the cut proceeded, and the tool would therefore plane a convex surface.
Thus the direction of the angle in which g is fixed governs whether the surface planed shall be a concave or a convex one, and it is plain that the amount of concavity or convexity will be governed and determined by the amount of angle to which g is set to the planer table.
When the chuck is not required to plane curved surfaces the bar g is altogether dispensed with, and the chuck becomes an ordinary one possessing extra facilities for planing taper work.