slotting machines with vertical cutting movement differ from planing machines in several respects, to which attention may be directed. in slotting, the tools are in most cases held rigidly and do not swing from a pivot as in planing machines. the tools are held rigidly for two reasons; because the force of gravity cannot be employed to hold them in position at starting, and because the thrust or strain of cutting falls parallel, and not transverse to the tools as in planing. another difference between slotting and planing is that the cutting movement is performed by the tools and not by movement of the material. the cutting strains are also different, falling at right angles to the face of the table, in the same direction as the force of gravity, and not parallel to the face of the table, as in planing and [135] shaping machines.

the feed motion in slotting machines, because of the tools being held rigidly, has to operate differently from that of planing machines. the cross-feed of a planing machine may act during the return stroke, but in slotting machines, the feed movement should take place at the end of the up-stroke, or after the tools are clear of the material; so much of the stroke as is made during the feeding action is therefore lost; and because of this, mechanism for operating the feed usually has a quick abrupt action so as to save useless movement of the cutter bar.

the relation between the feeding and cutting motion of reciprocating machines is not generally considered, and forms an interesting problem for investigation.

(1.) name some of the differences between planing and slotting machines.—(2.) why should the feed motion of a slotting machine act abruptly?—(3.) to what class of work are slotting machines especially adapted?