VERITAS Mk.II, Руководство пользователя

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34
Veritas
®
Mk.II Power Sharpening System
Buffing or Stropping Chisels
Some woodworkers touch up their chisels between
sharpenings on a felt buffi ng wheel or a leather belt on
a belt sander; either would be charged with a buffi ng
compound fi rst.
There is nothing wrong
with either system
as a quick fi x, but I
recommend that you
never buff the face
of the chisel. Almost
invariably you destroy
the fl atness. Similarly,
you will fi nd that you
are not saving time at all
if you round the bevel. I
also recommend using
only the side of the
felt wheel to minimize
bevel rounding. The
bevel rounding caused
by a leather belt on a
belt sander is negligible
if good technique is
used (i.e., honing only
over the platen where
the leather can fl ex the
least, and honing only
at a small incremental angle increase). This method is all
made even easier if a micro-fi nishing belt is used on the
belt sander instead of a leather belt. There is no fl exing,
and the fl at joins even eliminate bumping.
Utility Bevel-Edge Chisels
Woodworkers who own only one style of chisels usually
have bevel-edge chisels, the workhorses of the shop.
This makes it a bit diffi cult to recommend sharpening
angles, since the chisels will see use in all types of wood
and in all activities from paring to mortising.
Usually a 25° bevel angle is adequate for these chisels,
except in the smaller sizes. As you may have noticed,
you will more frequently roll the edges on narrow
chisels than on wide ones.
The reason for this is fairly straightforward. Assume
that you are going to do some light mortising with a
1-in. chisel and a
1
/
4
-in. chisel. If you use mallet blows
with the same force on the
1
/
4
-in. chisel as on the 1-in.
chisel, the
1
/
4
-in. chisel will be subjected to four times
the deforming force as the 1-in. chisel. Since we all
tend to forget that the force of mallet blows should be
modifi ed according to the width of chisel we are using,
we frequently overstress narrow chisels. Accordingly, it
is a good idea to put a higher bevel angle on narrower
chisels (30° is appropriate). Such narrow chisels are
seldom used for light paring so this steeper bevel angle
is justifi ed for edge retention.
If you have only one set of chisels you might even
consider putting a bevel angle as low as 20° on the
largest chisel, remembering that if it is used for any
light mortising, the mallet blows should be light as well.
Since the largest chisel is most frequently used for paring
this will give you the greatest versatility in a single set
of chisels. If you never use your bevel-edge chisels for
If you touch up chisels between
sharpenings on a felt buffing
wheel, use only the side of the
wheel to minimize bevel rounding.
As a general principle, quenching tools during grinding is
a substitute for good technique. The drawing below shows
what happens to a quenched tool.
1. Tool at room temperature before grinding. The thin
edge heats and cools very rapidly in comparison to
the main blade body.
2. As the tool heats up during grind ing, it expands.
3. If the metal were perfectly elastic, this is what the tip
would look like as it first hit the water and the thin tip
cooled more rapidly than the rest of the blade.
4. But metal is not perfectly elastic, and as it shrinks, tiny
cracks are cre ated in the edge.
5. When the entire blade has cooled, the cracks may
become invisible but they will be there.
To Quench or Not To Quench
Where rust pits intersect the edge of the blade, you get a
blade nick. Some old tools that have been allowed to pit
deeply are hardly worth restoring. Unless the face of the tool
can be brought to a mirror finish, the same as the bevel, you
will continue to have problems when repeated sharpenings
cause the receding bevel to encounter craters in the face.
A key to preserving the sharpness of tools is the
prevention of rust — not just the visible rust that noticeably
pits a blade but the slight rusting that comes from testing
a blade with your thumb or finger. Rust like this, although
visible only under an electron microscope, is already
causing deterioration of the keen edge.
Rust Never Sleeps
Dotted lines show normal width
at room temperature.
1 2 3 4 5
A pitted blade edge.