|LOWERING THE BED ANGLE ON A BLOCK PLANE
If you have a short lever cap on your block plane, it will apply pressure behind the machined portion of the bed caus ing the end of the blade to be lifted away from the bed. To reduce blade chatter caused by this flaw, you have to lower the bed angle so that the blade rests on the bed at the mouth, not 1/4 in. back of the mouth. To dress the bed, strip the plane (removing the adjustable nosepiece) and file the bed, letting the file pass through the open mouth and using the frog post as a guide since it is several degrees below the blade line on all modern block planes. (The low post is another flaw, but at least it works in your favor for this process.)
If you find it too difficult to get even seating of the tensioned blade along the entire bed, you can relieve just the back part of the bed so that the blade only touches at the mouth. That is still better than the condition you are correcting.
The lever caps on both of the Stanley block planes are about 1/4 in. short of
what they should be, the lever cap on the Record #060-1/2 is nearly 1/2 in. short.
To compensate for this, you should lower the bed angle by 1° or 2° to
ensure that the pressure of the short lever cap does not cause the blade to arch
from the front of the bed (see previous page). Assuming that you have
done that and all the other necessary tune-up procedures, you can turn your attention
to the blade.
The standard block plane (#9-1/2) has a bed angle of 20°. Since the blade is
bevel up, if we put a standard 25° bevel on the blade, we will end up with a
cutting angle of 45°. This just happens to be the same cutting angle that we
have for a smoothing plane, which has a bed angle of 45° but where the blade
is used bevel down. So when you sharpen the blade of your standard block plane
at 25°, you produce what is in essence a smaller smoothing plane.
But there is nothing to say that you can’t put two bevels on a plane blade. You
can easily grind and hone a 15° bevel on the blade and then put a 10° back
bevel on the face of the blade (as shown in the top drawing at right). This would
still leave you with a 25° included angle, but you would now have reduced
your cutting angle from 45° to 35°. You are still left with a 10° relief
angle, which is perfectly adequate for block-plane use.
Possibly more significant, you have sharpened the blade of your standard block plane in a manner that will give you a lower cutting angle than someone who sharpens a low-angle block plane in a standard fashion (12° bed angle plus 25° bevel, a total of 37°).
All of this dazzling footwork with bevel angles now raises the question, “Why do we bother with a low-angle block plane?” It is a good question. The answer is that lower bed angles not only let you use lower cutting angles but they also align the blade more closely with the direction of cut, there by minimizing chatter. The lower you make the bed angle, the closer you approach the function of a chisel, which does not chatter.
This article is excerpted from The Complete Guide To Sharpening by Leonard Lee.