In some cases (eg. cutting end grain) it is advantageous to skew the plane. This means the length of the plane will be at an angle to the direction of cut along the grain. Skewing reduces the effective cutting angle of the blade. Skewing the plane reduces shaving width. The plane handles are not in line with the blade so for larger skew angles the plane may be difficult to push.
Table: Effective Cutting angle for different skew angles using 45 degree bed angle plane.| Skew Angle (degrees) |
Effective Cutting Angle (degrees) |
|---|---|
| 0 | 45 |
| 10 | 44.6 |
| 20 | 43.2 |
| 30 | 40.9 |
| 40 | 37.5 |
| 50 | 32.7 |
| 60 | 26.6 |
| 70 | 18.9 |
| 80 | 9.9 |
| 90 | 0 |
In other cases it is best to not skew the blade. In figured woods like curly maple, the grain quickly alternates direction. You will be planing with the grain and against the grain as the grain alternates. A lower effective cutting angle tends to pry the wood fibers out when planning against the grain. When even a zero degree skew is not good enough to avoid tear out you can put a back bevel on the blade. I believe the effect of cutting angle is discussed well in Leonard Lee's book The Complete Guide to Sharpening. You can also read about it in the instructions on Lee Valley's website for the Veritas bevel-up planes. At the bottom of the instructions (a pdf file) for the Veritas low angle smoother or jack plane there are microscope pictures included and I think the text and pictures are from Leonard Lee's book. Ron Hock recommended a book by Brian Burns called Double Bevel Sharpening (here double bevel means front and back bevels) which is available from Luthiers Mercantile International . The notes on Steve Knight's website for his bench planes contains most of the practical information about using different cutting angles with different woods. Steve recommends back bevels as a way to increase cutting angle to people who can afford another blade but cannot afford another plane with a different bed angle. Back bevels are a good way to increase the cutting angle without increasing the bed angle. The lower the bed angle the less likely chatter occurs as the blade is aligned better with the cut. (I believe that low angle smoothers and jack planes are gaining popularity because of this blade alignment issue.) Also Brent Beach suggests that back bevels are a good way to remove all the worn areas of the blade. Brent's method is not the only way to remove the wear but his method could waste less metal with each honing when compared to keeping the back of the blade flat.
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