Though much has been written
on this subject I feel there is room for more.
At the risk of redundancy hopefully I can clear some of the
confusion. Also when I speak of certain features I want you to be
able to come back here for reference when required. For
clarity I will use specific names for certain features plus
pictures and sketches that identify them.
Saw tooth geometry involves three major angles that must be
understood; rake, fleam and slope.
These angles are always
relative to the tooth line and or the plane of the plate. When I
speak of the plate, think of the plane of the plate. When I
mention the tooth line, think of a plane that is perpendicular
to the plate and touches the tips of the teeth. For this
discussion consider the tooth line straight.
Rake is the angle of the leading edge of the tooth. If a saw is
said to have zero rake then the leading edges of the teeth are
perpendicular to the tooth line. The rake angle could be either
positive or negative although, handsaw teeth rarely have
Positive rake means that the tooth’s leading edge leans toward
the toe of the saw and in the direction of the cut.
Negative rake means that the leading edge of the tooth leans
toward the handle of the saw and away from the cut direction.
Rake is important for several reasons but of primary concern is
the force required to push the saw as wood is severed and
removed. If the teeth are two positive (think hooked) or lack
enough negative angle then they dig to deep and tend to stall in
the work piece. The saw is hard to start and tends to chip out
the wood at the exit point.
Negative rake acts as a sort of depth stop. Too much and
the saw cuts slowly because the teeth are skidding over the wood
more than cutting or digging in.
Too little and the saw digs to deep and is not able to
completely sever the wood fibers before the gullets bottom out
or the force required to push the saw exceeds the push force
available or worse yet, the stiffness of the plate.
The rake angle is often adjusted for various reasons, ie, the
intended material and ease of starting the cut.
The recognized modern commercial standard for rake on a Rip Saw
(if there is such a thing) seems to be 8 degrees negative but
there is good reason to vary it such as tooth pitch and the
material to be cut.
A standard Cross Cut Saw usually has 15 degrees of negative
rake, a bit more than a rip saw. The rake angle is less critical
for a crosscut saw and varying it makes less difference in
performance unless it is taken to extreme.
Fleam is the second angle of the tooth’s leading edge or cutting
face. It is measured as zero being perpendicular to the saw
This angle is always neutral to positive for a hand saw, meaning
that the fleam always leans away from the leading edge and
towards the saw handle. Unless the fleam and slope angles are
zero, the fleam surface is actually a compound angle relative to
the plate and the tooth line.