continuous cutting action is prevented, because soon the
blade cannot force apart the sides of the cut made by the advancing
edge, and the knife is brought to rest. In this case, it is
practically only the first action which has taken place.

Both the actions, the cutting and the splitting, must take place
together to produce a true continuous cut. The edge must always be in
contact with the solid material, and the blade must always be pushing
aside the portions which have been cut. This can happen only when the
material on one side of the blade is thin enough and weak enough to
be readily bent out of the way without opening a split in front of
the cutting edge. This cutting action may take place either along the
grain, Fig. 61, or across it, Fig. 62.

The bending aside of the shaving will require less force the smaller
the taper of the wedge. On the other hand, the wedge must be strong
enough to sustain the bending resistance and also to support the
cutting edge. In other words, the more acute the cutting edge, the
easier the work, and hence the wedge is made as thin as is consistent
with strength. This varies all the way from hollow ground razors to
cold-chisels. For soft wood, the cutting angle (or bevel, or bezel)
of chisels, gouges and plane-irons, is small, even as low as 20 deg.;
for hard wood, it must be greater. For metals, it varies from 54 deg. for
wrought iron to 66 deg. for gun metal.

[Illustration: Fig. 61. Edge and Wedge Action With the Grain.]

[Illustration: Fig. 62. Edge and Wedge Action Across the Grain.]

Ordinarily a cutting tool should be so applied that the face nearest
the material lies as nearly as possible in the direction of the cut
desired, sufficient clearance being necessary to insure contact of the
actual edge.

There are two methods of using edge tools: one, the chisel or straight
cut, by direct pressure; the other, the knife or sliding cut.

The straight cut, Fig. 63, takes place when the tool is moved into the
material at right angles to the cutting edge. Examples are: the action
of metalworking tools and planing machines, rip-sawing, turning,
planing (when the plane is held parallel to the edge of the board
being planed), and chiseling, when the chisel is pushed directly in
line with its length.

[Illustration: Fig. 63. Straight Cut.]

[Illustration: Fig. 64. Sliding Cut.]

The knife or sliding cut, Fig. 64, takes place when the tool is moved
forward obliquely to its cutti