How a Crosscut Saw Really Cuts
There seems to be some miss-information around about how a crosscut saw cuts. The basic idea that the cutters score the wood and the rakers scoop out the cut wood is correct.
Most have seen drawings like this that are supposed to show how a saw cuts:
How the saw advances down through the wood and why there is a need to have the rakers shorter then the cutters is not shown.
Some have also seen images like this:
This image is reported to show that the reason rakers need to be shorter then the cutters is because of spring back in the wood. However, this image fails to show how the saw advances down though the wood.
Here is what I believe a more correct representation of how a saw cuts and advances through the wood:
If you look close at the “How Crosscut
Saws Cut” drawing you will see that this set up would actually pull little
whiskers on one side of the noodle.
If a sawyer looks close at noodles when starting to pull
some whiskers they will see whiskers on just one side at first. The rakers
are scooping the depth of first cutter before the cutter but actually scooping
deeper then the second cutter in front of the raker.
This is not by design but just happens to be the way I
drew it. It
just makes the drawing a little cleaner because it does not show the score line
under the rakers.
I believe that the spring back theory that is
supposed to explain the need for shorter rakers is not correct.
The need for shorter rakers is fully explained by the
physical motion of the saw and how it moves through the wood.
Depending on how sharp the cutters are there could be a
small amount of spring back but it would is a very small part of the reason for
shorter rakers. In my
actual test of wood spring back on dry hard and soft and green soft woods the
measured spring back is in the range of one to three
thousandth of an inch. In general the cutters will cut into soft wood
deeper then hard wood so the idea that the softer the wood the shorter rakers
need to be and vise versa is correct.
Comments, suggestions or questions are
always welcome.
Jim Thode