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Bevel Up versus Bevel Down?





It is often said that the wood cannot tell whether a plane is BU or BD. That is true - it cannot tell the difference when both planes have the same cutting/included angles, and when the blades are equally sharp, and when they are both thick enough to avoid distortion.

However, there are pros and cons for both types of planes. And here I must stress that the conditions of use as to be described are as they apply in my shop. This will be the same for some and not for others.

High cutting angles are preferred for interlocked grain. For some, 55 degrees will do. For much of the woods I work at least 60 degrees is needed, and yet some even higher angles - David Charlesworth often refers to using 70 degrees. He does this in a BD #5 1/2 with a common pitch frog (45 degrees) and a 25 degree backbevel.

Achieving these high angles are easier using a BU plane - simply alter the secondary bevel on bevel face. Unless it has a high enough bed/frog, a BD plane will require two bevels - one on each side of the blade.

Low cutting/included angles are also the domain of the BU plane. Planing across the grain and end grain is best served by a low cutting angle. Few BD planes can go below common pitch. The 12 degree bed of the BU plane, along with a 25 degree bevel, create an included angle of 37 degrees.

So, in effect, the bottom line is that a BU plane has a wider range than a BD plane.

But that is only part of the story.

The advantage of a BD plane for me is that the blade is easier to hone freehand. The disadvantage of the BU plane for me is that the blade generally requires a honing guide for the high secondary bevel angles – and it is impossible to hone a 50 degree secondary micro bevel, plus it is extraordinary work to create a camber on a thick blade with a single, flat high bevel. Better to use a honing guide and a high secondary bevel on a low primary bevel, especially if you want a camber.

So I tend to reserve the BU planes for the extreme angles. I do have BD planes with high bed angles, in fact I have an equal number of BU and BD planes for planing difficult grain. I see the advantage of BD planes in their ease of honing - create a hollow grind and simply freehand on that.
This issue does not exist for those who use honing guides for all their sharpening.

The aim in smoothing is to plane with the lowest angle that produces tear out-free surfaces Lower angles tend to create smoother finishes. However this is not always possible with interlocked grain. In fact, in my experience, it is rarely achieved. It is safer to go with a high cutting angle and so minimise the risk of tear out. And if you really want to plane at a lower (e.g. common) angle, there is no reason that a BU plane cannot be used as easily as a BD plane. In fact, many would argue that the BU plane has greater potential and ability at any angle in a comparison with a BD plane simply because it does not require a double iron (the irons are generally thick enough), and the blade is supported further than is the case of the BD plane's blade. In practice I think that the thicker blades minimise the latter advantage of the BU plane. I do think that it remains a weakness for BD Stanley planes with thin and flexible blades.


Regards from Perth

Derek

April 2011