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Grinding area and grinding pressure
Flat or Oval Skews with a Curved Edge
Straight edge. Large grind-
ing area. Same as the entire
grinding bevel. Low resulting
grinding pressure. Grindstone
requires activating.
Convex edge. Smaller grinding
area. Higher resulting grinding
pressure. The grindstone works
more effectively.
You can put a curved (convex) edge on both your flat and oval skews. You pivot the jig with
the tool on the Universal Support to create the curve. This curved edge has certain advan-
tages and has been popularized amongst others by the Australian professional woodturner
Richard Raffan. He prefers a slightly curved edge, which is shown in full scale on the next
page.
To achieve this shape, you need to set the SVS-50 jig on 30° instead of 20° for the straight
edge shape. Even here, you will need to remove quite a bit steel, which can take 10–20
minutes depending on the original shape. But again, this is a once only task, from which you
will benefit at future sharpenings.
Since the contact area against the grindstone on a convex edge is smaller than on a plain
edge, the resulting grinding pressure is higher when applying the same force on the tool.
(The grinding pressure is the force you apply onto the tool divided by the grinding area.)
A certain grinding pressure is required to maintain an active grindstone surface so it does
not become glazed. When shaping or sharpening a skew chisel with a straight edge, which
has a large grinding area, you therefore need to re-activate the grindstone frequently with
the Stone Grader SP-650.
Since the grinding pressure is higher – even with the same force applied on the tool – on a
skew with a convex edge, the grindstone activates itself and therefore grinds more effectively.
This is why a skew with a convex edge is shaped faster than a skew with a straight edge.