s also tapers from the teeth to
the back. All these tapers gives stiffness where it is most needed.
It is made wide for the sake of giving steadiness in sawing. The fact
that it is thinner at the back than along the teeth gives it clearance
in passing back and forth in the kerf, but the friction is still
great, especially in sawing soft or damp wood. To avoid this binding
still further, the teeth are "set" alternately one to one side and the
next to the other, and so on.

[Illustration: Fig. 87. Rip Saw Teeth: A-edge view, B-side view,
C cross-section. Crosscut-Saw Teeth: A'-edge view, B'-side view,
C'-cross-section.]

The size of saws is indicated by the length of the blade in inches.
The coarseness of the tooth is indicated by the number of "points"
to the inch. "Points" should not be confused with teeth as there is
always one more point per inch than there are teeth. For example,
a five point rip-saw has five points to the inch but only four
full teeth, Fig. 87. Rip-saws run from 4 to 7 points per inch;
crosscut-saws from 6 to 12 points per inch.

In general, saws are of two kinds, rip-saws and crosscut-saws.

The _rip-saw_, Fig. 87, may be thought of as a series of chisels set
in two parallel rows which overlap each other, for each tooth is filed
to a sharp edge which, at each stroke, chisels off a small particle
from the end of the wood fibers.

The shape of the teeth is the result of experience in uniting a number
of factors: as, strength of the individual tooth, the acuteness of
the cutting angle, and the ease of sharpening. The steel of a saw is
softer than that of a chisel, in order that it may be filed and set.
Hence it is weaker and the edge cannot be so acute. A typical form
of tooth is shown in Fig. 87, in which A is an edge view, B the side
view, and C a cross section. The angle of each tooth covers 60 deg., one
side, the "face", being at right angles to the line of the teeth. The
cutting edge runs at right angles to the sides of the blade.

This arrangement works with entire success along the grain, but if a
rip-saw is used to cut across the grain, since there is no provision
for cutting thru the fibers, each tooth catches in them and tears them
out, thus leaving a rough and jagged surface.

In the _crosscut-saw_, therefore, the teeth are filed to points, and
the cutting edge is on the forward side of each alternate tooth.
In Fig. 87. A' is the edge view, B' is the side view and C' is a
cross-sec