Jeffrey Makiel
01-01-2010, 10:44 PM
I often hear folks talking about feeding stock on a slight angle to create a "shear cut". However, I don't think it's a shear cut. Rather, it's still a flat cut. That is, when the straight cutter hits the wood, the entire edge of the blade enters the wood at the same time. Therefore, a skew feed is still 'slapping' the wood.
To me, a shear cut is when one end of a cutter initially engages the wood, then the point of contact moves along the length of the blade as it rotates until it reaches the other end of the cutter. This can only happen when the edge of the blade is at an angle relative to the rotating axis of the cutterhead...not the angle of wood feed.
A Shelix is an example of a true shear cut. Its little cutterheads are set an angle to the rotating axis of the cutterhead. The Grizzly spiral cutterhead simulates this effect in a segmented fashion using several small straight cutters parallel to the rotational axis of the cutterhead but mounted in an overall spiral configuration.
Sometimes I try to skew feed boards into my little planer or jointer having straight knives. This has nearly insignificant results for me because I've never found a board that had perfectly straight grain. Aside from quartersawn, the grain usually shifts side to side, and up and down, thus changing the effective skew angle anyway.
If I ever upgrade my machinery, I will be going with a spiral or helical cutterhead. I hear many positive things about them regarding reduced tearout.
Perhaps I'm just petty. Maybe I should have a New Year's resolution to get out more often. :)
-Jeff :)
To me, a shear cut is when one end of a cutter initially engages the wood, then the point of contact moves along the length of the blade as it rotates until it reaches the other end of the cutter. This can only happen when the edge of the blade is at an angle relative to the rotating axis of the cutterhead...not the angle of wood feed.
A Shelix is an example of a true shear cut. Its little cutterheads are set an angle to the rotating axis of the cutterhead. The Grizzly spiral cutterhead simulates this effect in a segmented fashion using several small straight cutters parallel to the rotational axis of the cutterhead but mounted in an overall spiral configuration.
Sometimes I try to skew feed boards into my little planer or jointer having straight knives. This has nearly insignificant results for me because I've never found a board that had perfectly straight grain. Aside from quartersawn, the grain usually shifts side to side, and up and down, thus changing the effective skew angle anyway.
If I ever upgrade my machinery, I will be going with a spiral or helical cutterhead. I hear many positive things about them regarding reduced tearout.
Perhaps I'm just petty. Maybe I should have a New Year's resolution to get out more often. :)
-Jeff :)