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Handsaw Sharpening & Traditional Tools with Mike Hagemyer


 
  Understanding Handsaw Geometry and Terms by Mike Hagemyer 1 of 5  

 

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.

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 plate.

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.


 
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