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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 ...

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


July 2020