Beyond a Sharp Edge: A Sharpening Strategy
I
love using handtools and I dislike sharpening. I dislike sharpening
so much that I became as expert as I could on sharpening just to find
the most efficient shortcut.
There are certain basic rules I
currently follow that I present below with the intention of hopefully
making the task easier for others.
There are a few basic
factors that I consider too elementary to discuss but mention because
they are the place to start. The given is that the front and back of
a blade must be honed to the same high level. But high level of what?
"Sharpness"
is really about "smoothness", and one can only be as smooth
as the side with the lesser surface. So you must use, for example,
your 8000 waterstone equally on both the front and the back of the
bevel. The back of the blade is as important as the front of the
bevel edge. This article is all about achieving this end ...
And
then the aim is to maintain the sharpened steel at that level as long
as possible, because - just in case you have forgotten - I am not a
one who enjoys sharpening. The following is how you get to do that
...
Lastly, there are differences in the way one approaches
bevel up (BU) or bevel down (BD) plane blades. For some years I tried
to treat BU blades the same as BD blades … and struggled.
Finally I accepted that they needed a different approach.
Secondary
bevels and backbevels
Terminology!
Ugh!!
In my book, a secondary bevel is a bevel that one adds to the primary bevel. As such it must be at a higher angle than the primary bevel. For example, a primary bevel may be 25 degrees. The secondary bevel may be anything from 26 degrees upward.
Sometimes secondary bevels are referred to as “micro bevels”. This is both correct and incorrect at the same time. A micro bevel only refers to the size of the bevel and, obviously, it is a very tiny bevel (“tiny” meaning it can be lessthan or about 0.5mm wide).
Of course, if you have a
secondary bevel (that is, a bevel at a different angle to the primary
bevel), then it is possible to have a “secondary micro bevel”.
Secondary micro bevels really complicate
sharpening. Sometimes they are a necessary evil (see BU planes,
below). Sometimes they really work magic. But sometimes they are a
Royal Pain in the Whatsit.
I think this way about David
Charlesworth's "Ruler Trick". This is a terrific -
brilliant! - strategy for speeding up the sharpening of old blades -
ones with pitted or warped backs - which is what I believe David
conceived the method to be. It should not be necessary to use on
modern blades, which now either arrive flat or require very little
work to become flat. As you will see, the Ruler Trick actually makes
sharpening more difficult in the long run when you follow the same
sharpening philosophy as I.
My
approach to sharpening keeps re-sharpening
in mind – that is, minimising the amount of time and effort
that will go into sharpening a blade.
I cannot emphasize this
enough. I really do not want to be going back to my waterstones all
the time. I also do not want to rely on the steel to be so tough
that it holds its edge a longer time (such as replacing HCS and A2
with HSS) - because then there will be an emotional aversion to
sharpening the dull blade. If sharpening can take just a few seconds,
or hardly be needed at all, then it will not feel intrusive.
Bevel
Down ....
All my BD plane blades
and all chisels are hollow ground (even - increasingly - my Japanese
chisels). Some BD plane steel is best with a primary bevel of about
30 degrees, some will cope with about 25 degrees. I have found that
A2 steel improves some as it is ground back and, while it is
reportedly best with a 30 degree bevel, I have not had a problem with
edges folding when a 25 degree bevel is used in a LA Jack on the
shooting board. It also gets very sharp, certainly sharp enough for
my purposes. At one time I considered that 30 degrees would be too
high in a paring chisel (my HCS Bergs are at 20 degrees, which is
considered by some to be ideal), but the A2 Blue Spruce dovetail
chisels get very sharp and hold a good edge at 30 degrees. As do my
Iyoroi bench chisels.
I prefer to hollow grind on a Tormek. I
also have a half-speed 8" grinder with a blue 46 grit Norton 3X
wheel, which is provides a much cooler grind than any other dry
grinder I have experienced. However the Tormek makes it so much
easier to grind to the very edge of the bevel. With so little steel
to hone, at this point, one can easily get away with just a 1000 (to
flatten the bevel) and 8000 (to smooth and polish the steel)
waterstones.
Incomplete at this
stage, this is my Sharpening Centre: draining board for waterstones,
10” Tormek and 8” half-speed grinder
The
other point is that I prefer to hone freehand. Hollow ground bevels
make this easy. I hone directly over the hollow, using the hollow as
a reference for stability. Nothing machismo here. Just hold the bevel
flat on the hollow and move it until you feel an even wire edge (your
guarantee you have not dubbed the edge). It takes about three swipes.
That is all. I use a side sharpening technique as this also avoids
the danger of dubbing. You end up with a micro bevel that is coplanar
with the back of the bevel. This is also relevant as you will see
shortly.
The importance of avoiding a secondary bevel
("grinding at 25 and honing at 30") is that re-sharpening
is made easier. I depend on a strop to maintain the edge between
honing (There is an article
I
put on my website recently on the use of a strop). This
is the crux of the matter.
The issue here is that it is extremely difficult to maintain the angle of a microbevel when freehanding on a strop. It is easy enough to create a microbevel on a stone, but returning to it later is a recipe for dubbing. And that is the rub.
Leather
strop with green rouge/baby oil mix.
Another
of the reasons I avoid a non-coplanar secondary bevel is that adding
one to a chisel is like using the Ruler Trick with plane blades. What
it does is make stropping more difficult, but also removes the
registration from the chisel bevel when using a chisel bevel down. I
know that some argue that they can pare with a non-coplanar bevel,
but I am simply pointing out that a coplanar bevel is more reliable
and easier to use.
Hopefully you are still with me.
Bevel
Up ...
So
on to BU planes. Some are concerned that BU plane blades suffer
premature dulling as a result of a larger wear bevel - and I am not
refuting that this occurs or that it causes deterioration of a
plane's performance. However I do not experience any issues myself,
and this may be due to my blade maintenance strategy.
Where BU
blades differ from BD plane blades is that the cutting angle is a
combination of the bed and bevel angles. Since I use steep cutting
angles on the BU smoothers and want to add a little camber, it is not
appropriate to attempt to hollow or flat grind these at that angle.
That is why I came up with a cambering strategy for BU blades in this
article.
I fought against using a honing guide for a long while, but
eventually just accepted that BU planes must be done this way. While
the bevel angle is relatively unimportant on a BD plane blade, the
accuracy of it is all
important
on
a BU plane blade. This is what turns so many older woodworkers off BU
planes. However their performance is just so good that I will put up
with the extra rigour of a guide.
Cambering
a BD blade using the Veritas Honing Guide MkII
The problem with using a
secondary/microbevel on the BU blade is that it restricts stropping
for edge maintenance. Since you cannot get away without using a
microbevel, stropping can only take place on the back of the blade.
So - full circle - you cannot use the Ruler Trick as it would prevent
stropping. Of course, ignore all the above if you do not plan to
strop. My sharpening system is built around stropping.
The act
of stropping the back of the BU blade is what removes the “wear
bevel”. I simply do not allow it to get to the point where it
might intrude (I empasize "might" since there are many BU
plane users who do not experience in practice what is stated in
theory).
So there you have it. An initially complex strategy
to an outwardly simple issue, but one that reduces to a simple
strategy for what is in effect a more complex issue!
Regards
from Perth
Derek
June 2009
