Work Sharp Sharpening System - Manual (Page 25)

Before we move on,
there are a couple of
things to note. First, re-
member that in this se-
quence we used a four
plate, seven grit se-
quence instead of the
two plate, four grit se-
quence that comes
standard with the Work
Sharp. The standard set
up works very well and
is all most will want or
need starting out.
Adding additional plates
is a convenience, not a
necessity, but I think a
lot of you will wind up
with the leather strop plate and at least
one more glass plate, as I did.
Keeping your grits in an orderly progres-
sion means you can mount the first plate
coarse grit down and use the next finer
grit that is on its top surface to do the ini-
tial flattening of the back.
Making the back flat is far more important
than most people think as they usually
only look at the cutting edge from the
bevel side. If the back is not exception-
ally flat, the bevel will intersect the back
cleanly across part but not all of the cut-
ting edge. If the back is concave, the
center will be a sharp edge but the outer
edges will not be. If the back is convex, it
is just the opposite.
If you keep grinding on the bevel, you will
eventually reach the point where there is
a sharp edge across the whole width, but
it will not be a straight edge. The edge
will curve upward relative to the back if
the back is concave and downward if it is
convex. Both conditions would make the
chisel hard to use effectively as it would
produce scoop marks or humps instead
of a nice clean flat surface.
If you were using such a chisel to clean
the bottoms of through dovetails, the joint
would not fit well even if it was cut spot
on. If you were using it to form tenon
faces, the tenons would not fit tightly to
the mortise walls, weakening the joint.
So, make sure you get the back really flat
initially before you proceed with the
bevel. It is only important that an area
about an inch back from the cutting edge
be flat. By using the very flat top surface
of the abrasive on the top glass plate on
the Work Sharp, it is easy to achieve.
You don’t need to use an overly coarse
grit on the back since all it needs to be is
flat. The cutting edge will be formed by
the bevel. A sharp edge is the intersec-
tion of two faces coming together at an
angle, in this case the flat back of the
chisel and the 25 degree bevel angle on
the face of the chisel.
Note the fine curl being cut at a 45
degree angle across end grain.
With a less sharp chisel the fibers
would normally shatter instead of
curl like this.