Hand Tools Archive
Sorry, here's a clarification.
Upper side: The side of the blade that the shaving passes over. It's "up" when in the plane.
Lower side: The side of the blade that is facing down when in the plane.
So, on a bevel-down plane:
upper side = back
lower side = bevel
And on a bevel-up plane:
upper side = bevel
lower side = back
I think the upper side has more wear, regardless of BU or BD plane.
I showed only the back of a BU and BD blade in those pictures. (I implicitly assumed that the wear of the upper and lower sides of the blade will be similar for both types of planes.)
With my microscope equipment, it's hard to directly compare the wear of the upper side of the blade for BU and BD planes. In other words, it's hard to directly compare the wear on the bevel side and back side of a blade. This is because I can't light them in the same way.
When I look at bevel side of a blade, the surface tilted 25-30 degrees from perpendicular. In the bevel side case, I can position the light so that light reflects directly off of it and right up into the lens. (Not that I generally position the light that way for pictures, but this just illustrates one thing I can do.)
When I look at the back of a blade, the surface is perpendicular to the direction of view of the scope. It's not possible in this case to hold the light in a place where light will reflect right up into the lens -- not even close. The light is way too big to position it close to the lens axis.
Here's an example of why this matters. When I took pictures of the bevel-side (upper side) wear on a BU plane blade, it had a texture and I wondered where it came from:
Presumably, a BD blade has a similar texture on the back (its upper side). But I can't light the blade in a way that shows it -- with the blade in the scope, I can only hold the light off to the side. So this is what it looks like:
They probably have the same kind of wear, but I can't look at them in the same way with the microscope.