The teeth on saws are classified by a number which represents
the number of teeth points along 25.4mm (1 inch) of the cutting edge,
including those at each end. The number is referred to as so many
points, the point size is one greater than the teeth per inch (tpi).
The teeth of ripsaws are relatively large, usually between four to
seven points. The larger tenon saws, say 30 to 40cm (12 in to 16 in),
usually have teeth of 12 to 14 points. Smaller saws for general bench
work also may have 14 points, but the smaller saws intended purely for
dovetailing may have teeth as fine as 22 or 24 points. Saws with fine
teeth should be used only for fine work.
Set of the teeth
The set of the teeth: Most saws have
“set” teeth;
i.e., the teeth are slightly bent outwards in alternate directions to
make a cut slightly wider than the saw blade thickness, this gives a
clearance so that the blade is clear of the sides of the cut. The set
should not be too much, as it will only mean that wood is being removed
“for nothin’”, meaning more resistance
and more work. To reduce the necessity for the amount of set, some
handsaw blades are taper ground, (the blade is ground thinner behind
the teeth), yielding additional clearance with only a small degree of
set required. Saws used for green wood (i.e. freshly cut timber) have
increased set as the sawdust from green timber is inclined to cling to
the blade.
Angle of handsaw teeth
The front angle of the teeth: The front of the teeth on some
saws are
straight across at right angles to the blade, so they present the wood
with a series of chisel-like edges, this will give a rough finish.
Other saws have teeth bevel-filed at an angle instead of being at 90
deg., the idea being that the series of sharp corners severs the grain
at each side, the waste wood between crumbling away as sawdust. The
angle at which the teeth are bevelled vary from about 45 (for softwood)
to 60 deg (for hardwood).
Angle of saw teeth
The pitch angle of the teeth: The pitch angle of the teeth to
the
nominal root line of the teeth, associated with this is the point angle
- the combination of these two angles determine the slope of the back
of the teeth. A large number of modern handsaws have hardened teeth to
prolong their useful life; these saws are, to an extent, 'throwaway'
tools as they cannot be easily sharpened when they become blunt.
