A saw is a piece of toughened steel with
teeth cut into one edge and a wooden or plastic handle. In some form or other,
saws have been one of the principal woodcutting tools for thousands of years.
The different types of saw for different jobs can roughly be divided into three
main groups:
Saws differ in the size and shape of the
blade, and the size, shape and number of teeth they have. Rip teeth, which are
designed for cutting down the grain of wood, work like small chisels. The front
edge of each tooth is more or less perpendicular to the saw edge and the back
edge slopes at about 30 degrees. If saws with teeth like this are used to cut
across wood grain, they tend to tear the fibres and leave a jagged edge. Rip
teeth are generally straight-sharpened the tip of each tooth is perpendicular
to the cutting line. Cross-cut teeth, which are designed for cutting across
wood grain, generally slope back rather more and are usually cross-sharpened
the teeth are sharpened at an angle to the saw so that the outside edge of each
tooth is pointed. Cross-cut teeth tend to cut through the wood fibres rather
like a knife. Fleam teeth slope back even more than cross-cut ones and have
symmetrical points. They cut equally well on the push and pull strokes.
Saw teeth are usually set teeth are bent
slightly outwards from the blade, alternately in each direction, so that the
width of the slot cut by the saw is greater than the width of the blade. This
prevents the saw jamming in the slot when cutting and lets you change the
direction of the cut slightly during sawing. An even set is essential: badly
set saws tend to wander.
For years, saw bladeshave been made from hardened steel which has been tempered to reduce the
hardness (and increase the toughness) so that the blade wears well but is still
soft enough to be sharpened with a file. More recently, however, saws have been
introduced which have 'hardpoint' teeth the tips of the teeth are hardened to
reduce wear. Saws with hard-point teeth can have several times the life of a
conventional saw, but they cannot be sharpened by conventional methods and they
are much more easily damaged when they meet a nail in their path.
There are, confusingly, two systems for
describing the number of teeth a saw has - both are still based on imperial
measurements. The first method records the number of complete teeth in an inch
length of blade. The second method states the number of tooth points in an inch,
starling on a point and including this in the count. The two methods can be
confusing since a saw with eight points per inch actually has seven teeth per
inch. The second method is the most widely used and the terminology is often
shortened to talk about an eight-point saw, for example. Saws with large teeth
generally cut faster but leave a rougher edge than saws with small teeth.
You might also want to learn how to cut
metal with hacksaw blades and how to choose a good circular saw among many.