Q. At your machining seminar, you mentioned about having a special saw tooth angle so that a radial arm saw would not dig into the lumber and stall. Can you repeat this, as it is indeed an issue for us?
A. Here is the info about saws. The angle between the face of the tooth and a line running to the center of the saw is called the hook angle. (With knives, the similar angle is called the rake angle.)
This angle, when large means that the saw is aggressive, trying to pull the wood into the saw (or for a radial arm saw, pull the saw into the un-sawn wood). As this angle gets smaller, the saw is less aggressive and you might have to even help the saw push into the wood to cut it.
At zero degrees hook or negative hook angles, the saw does not want to dive into the wood, so you will have to really push the wood into the saw (which is dangerous because the saw will actually be pushing back and the piece of wood can kick back at you violently and cause injury.
However, with a radial arm saw, this force means that the saw will not grab the wood and stall, but will actually require you to pull the saw through the cut…a safe procedure indeed. With a slightly negative hook angle on this saw blade, the saw will actually try slightly to move back to its resting position (out of the wood).
Note that with band saws in the shop, we often have zero or slightly negative hook angles. If we had positive angles, the saw would jump into the wood and might fly off the wheels. With negative angles, the saw runs against the various guides when cutting and the kickback is directed downward against the table.
Another note is that with a table saw and similar, we do want a positive hook angle to avoid kickback.
So, always get a saw blade that has the correct hook angle for the machine you are using. Most blades are clearly labeled.
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