The Unicorn Method
This is
the inspiration of David Weaver, who is really a sharpologist
extraordinaire. David was the drive behind the re-emergence of the
double iron, that is, the use of the chipbreaker for controlling
tearout.
More recently, he came up with the Unicorn bevel,
which we kicked around on WoodCentral forum. The Unicorn Method is,
in its simplest explanation, the buffing of the bevel of a chisel to
create a micro-micro .. a nano secondary bevel which, owing to the
higher angle, promotes a longer lasting edge. Not only does it do
this, as I discovered, but it also still leaves a very sharp edge.
And the good part is that it can turn a crappy, cheap chisel into a
performing demon!
Why
“Unicorn”? This is David’s joke about finding a mythical
creature that is both sharpness and endurance in a quick
process.
The understand the method, watch his video
...
https://m.youtube.com/watch?v=Do7FdOh6S9s
To
quote David, “It's
simply this:
*
grind a primary bevel at 20 degrees
*
hone (with a medium stone) a secondary bevel around 3 degrees higher
(not precise, just a little higher). No wasting time with wire edges
or anything ,just leave the wire edge in place
*
buff the chisel briskly in a cotton buff (charged with any reasonable
buffing bar) on a buffer for about 5 seconds held about 45 degrees to
the buffer wheel and moved about just a little. A light touch of the
back of the chisel on the very fluffy outside corner of the wheel
will remove any swarf or wax stuck around the back side”.
I will
state that it is not necessary to work with a 20 degree primary
bevel. Use 25 degrees, even 30 degrees ..
The
following is a post I wrote at WoodCentral ...
There
has been a great deal of interesting photography of buffed edges to
date. I don't have the microscope to add to this, and so I will just
take what has already been presented that provides evidence of
enduring edges. Edges which last longer are lovely, but ...
...
I want the edges also to be sharp and take the type of shavings that
are evidence of a working tool, not just a long-lasting, but dull-ish
edge. Rounded edges increase the cutting angles from 20/25 degrees to
40-ish degrees? I mean, chisels are not expected to act like BU
planes, are they? Or the scraping chisel of Bill Carter?
Then
I sharpened a chisel. Not just any chisel, but a Marples Boxwood with
a 20 degree bevel. Actually, 5 of them. I wasn't in my right mind
when I originally hollow ground them to 20 degrees - thinking that I
could do with a few chisels with low cutting angles for dovetails -
especially when they struggled to hold an edge at 25 degrees!
And
the new buffed edge? Well, it took amazing shavings. Amazing! And it
did not stop taking these amazing shavings .... which is a miracle,
since the blades of these chisels are made of cheese.
They
looked like this .. which is not the Marples, but a Stanley #60
chisel, which is equally poor (we all have a few of these for opening
paint cans). The wood is Tasmanian Oak (similar to White Oak)
...
Sharpening
system? Nothing much. To test all this out, I had a much used 6"
stitched mop soaked in Lee Valley green compound. This was chucked
into my lathe ...
The
wheel was spun at 1450 rpm, which is the speed of a half-speed bench
grinder in Australia. I use an 8" half speed bench grinder to
hollow grind blades, so it made sense to try the same speed.
The
bevel was presented to the spinning mop and angled about 10 degrees
(PLEASE
NOTE,
if you are reading about this method for the first time, that the mop
is spinning away from the edge).
This
resulted in a fine wire, and rather than buffing this off on the mop
as David has done, I wiped the back of the blade on a piece of
hardwood with green compound.
How
does one know that the Unicorn has been successfully created? Imagine
that you are looking at a dull blade. The edge will show light, which
indicates there is wear (the converse is that the absence of light
shows it is sharp or, rather, that the face meets the back
cleanly).
Now, after adding the nano bevel via stropping, this
light returns. If it is not there, then there is no rounded nano
edge. Too much of this and the edge is dubbed. Just enough and the
edge remains sharp (or sharper).
Having
satisfied myself several times over that this method worked, and that
it looked a Good Thing, I decided to purchase another grinder rather
rely on the lathe .
The white wheel on the right has now been replaced with a soft stitched wheel ..
Winston
Chang has made another short video about buffing the Unicorn edge on
chisels. This is excellent and shows what is involved and what
occurs. Necessary viewing!
Sharpening
chisels with a buffing wheel on Vimeo
Keep
in mind that Winston uses a simple drill and stitched wheel. This
takes more time than my set up simply because the drill rotates at a
slower speed. David uses a bench buffer. I am using a bench
grinder.
I
got to thinking about trying this out on plane blades. In fact, I did
so, and realised that it may not be a good idea. All the bench plane
blades I have are cambered. Planing with a buffed cambered blade
created shavings that were stringy, indicating an uneven edge. You
can get away with this in a chisel, but not a plane blade. I shall
try again, but that is my initial observation.
I
also tried this with block plane blades. Now this was different: 25
degree straight bevel, just like a chisel. But would it cut
differently, especially on end grain where low cutting angles are
expected to rule?
A
LN blade was hollow ground at 25 degrees, and then went through a
typical process of extra fine diamond stone/Medium and Ultra Fine
Spyderco ceramic stones, and a final polish on green compound-on-hard
wood. At least the green compound would be the unifying
medium.
The
surface/shaving on Jacaranda (the softest wood to hand) looked like
this ...
The
buffed edge looked like this ...
The
buffed edge felt sharper and left a cleaner surface.
This
was repeated on Jarrah end grain. First the honed blade ...
.. and the buffed edge …
Nothing
in the two? If so, that is a win.
Regards
from Perth
Derek
July 2020