Return the Unicorn… What Was Old is New Again?

[Jim Koepke]

While seated comfortably in the reading room and thumbing through an old Fine Woodworking (#39) from 1983 this article came to my attention:

441963

This guy was old in 1983. His technique was developed over many years including a few years in a machine shop during WWII.

Charles Riordan explains his preference for the hard felt wheel being due to the softer buffing wheel rounding the edge. With a hard wheel the secondary bevel is more flat and can be touched up on a strop before regrinding.

jtk

[Charles Guest]

While seated comfortably in the reading room and thumbing through an old Fine Woodworking (#39) from 1983 this article came to my attention:

441963

This guy was old in 1983. His technique was developed over many years including a few years in a machine shop during WWII.

Charles Riordan explains his preference for the hard felt wheel being due to the softer buffing wheel rounding the edge. With a hard wheel the secondary bevel is more flat and can be touched up a few times before regrinding.

jtk

Not even remotely new as you've noted Jim.

In fact, raised to art:

A series of felt wheels of varying stiffness, with polishing compounds to match. Amazon used to carry the system as well.

https://www.woodcraft.com/products/koch-sharpener-ht2000

From Nora Hall's website. She's been deceased for close to ten years I think:

https://www.norahall.com/tools_koch.shtml


(https://www.norahall.com/tools_koch.shtml)

[Eric Rathhaus]

Tage describes going from best sander straight to a buffer

[Charles Guest]

Shows it as well in his old dovetailing video.

[Winston Chang]

Using a hard felt wheel has a very different effect from using a soft buffing wheel. A major factor in the "Unicorn" effect from the soft buffing wheel is specifically the steepening of the edge. That's what makes the edge so durable. A hard felt wheel is also more likely to form a burr which you have to work off, whereas a soft buffing wheel pretty much eliminates the burr, even if you only use it on the bevel side.

A few people who have tried the hard felt wheel have not had the same results with it as with the soft wheel. I'm not saying the hard felt wheel is bad, but it does have a different effect.

[Jim Matthews]

I'm having my best results substituting the Cotton buff (with green compound) for stropping.

I tease off the wire edge before this last step.

Middling results on plane irons, VERY effective on chisels.

[Charles Guest]

Using a hard felt wheel has a very different effect from using a soft buffing wheel. A major factor in the "Unicorn" effect from the soft buffing wheel is specifically the steepening of the edge. That's what makes the edge so durable. A hard felt wheel is also more likely to form a burr which you have to work off, whereas a soft buffing wheel pretty much eliminates the burr, even if you only use it on the bevel side.

A few people who have tried the hard felt wheel have not had the same results with it as with the soft wheel. I'm not saying the hard felt wheel is bad, but it does have a different effect.

The Koch system has four different wheels, for what it's worth. In its original iteration, only two.

[Derek Cohen]

The Koch system aims at honing the bevel, which is at a “standard” angle of around 25-30 degrees. In other words, this is much the same as buffing the edge on a Tormek.

Other than being another buffing system, this is quite different from the Unicorn. The unicorn is a profile, and not a sharpening system. I suspect that this is what confuses many. It looks like the effort is going into honing or buffing an edge, but the effort is actually going into the creation of a steeper tertiary nano bevel, somewhere around 40-45 degrees. This is what promotes longevity at the edge .... and nano sized to avoid affecting penetration at such a high angle.

Regards from Perth

Derek

[James Pallas]

Just some thoughts on this. I don’t have a dog in the hunt. I have finished with a leather strop for a long time. I know others use MDF and such trying to keep the bevel flat. I tried that and gave up. I wonder if stropping on leather imparts a little of the same profile by rolling the edge a bit. Maybe Paul Sellers hard strokes on leather do the same. I don’t use his methods though. It always seemed to me that I got a better longer lasting edge on a leather strop. No scientific evidence just experience. I’ve buffed many carving tools on a cotton wheel but not bench chisels.

[Winston Chang]

It's definitely possible that stropping like Paul Sellers could round off the edge. If I recall correctly, in his sharpening video he strops it with very heavy pressure for 30 strokes.

For what it's worth, I also got a more durable edge by stropping at a deliberately high angle (about 40-45 degrees, on a bevel that was honed to 30 degrees on stones). It wasn't quite as good as the edge from the buffing wheel, but it's possible that with some practice and refinement of technique, the results could be comparable -- I only tried it twice with the strop. Test results here: https://chisel-test.netlify.app/#buck-brothers-stropped

[Jim Matthews]

It's definitely possible that stropping like Paul Sellers could round off the edge. If I recall correctly, in his sharpening video he strops it with very heavy pressure for 30 strokes.

I've done both. The approach taught by Paul was designed to tease off the wire edge, first. He was adamant not to roll the tool - to maintain a constant angle.

Using the buff is faster and it lasts longer.

[Jim Koepke]

I wonder if stropping on leather imparts a little of the same profile by rolling the edge a bit.

If the leather is particularly soft it is likely to give a little rounding to the edge.

Stropping is an art all to itself. My experimentation with the strop has shown me that careless stropping can decrease the sharpness of a honed edge. It can also increase the sharpness of an edge on the verge of sharp.

Just like folks today, the chisel and plane blade sharpeners of yesteryear likely tried all the same 'tricks' we do today.

jtk

[Mike Allen1010]

What relative angle between secondary bevel and buffing wheel are you guys using? I'm having good results with chisels and bevel up plane blades, but haven't really tried with BD blades. Apprentice the suggestions! Cheers, Mike

[Rafael Herrera]

On my BD irons, the angle of the bevel and the buffing wheel is maybe 45 degrees? I'm not measuring, I make the wheel ride the bevel without too much abrasion on the edge itself. I don't know if I'm doing it right or not, I'm unable to tell yet if I'm getting a better edge. The one thing I can observe is that I can get the iron razor sharp after the buffing wheel. I can get it razor sharp after the strop as well, but it takes a little more time.

Head over to the Wood Central web site and look at their articles page. David Weaver's article on the Unicorn profile can be found there.

[Winston Chang]

What relative angle between secondary bevel and buffing wheel are you guys using? I'm having good results with chisels and bevel up plane blades, but haven't really tried with BD blades. Apprentice the suggestions! Cheers, Mike

For bevel-down plane blades, I've found that you have to be more careful than for chisels and bevel-up plane blades. The reward, though, is that sharpening is faster and easier than the "regular" way with just stones, and the surface quality of the wood will be incredibly smooth.

You don't want to over-buff the blade and increase the edge angle past 45 degrees. If that happens, then the plane will feel a little weird when you use it and you'll find that you need to press down to keep it cutting, and you'll also have to advance the blade further than you normally would. Using a blade like feels similar to using one that's significantly dulled through use, except that it will leave a really, really smooth surface.

First things first. The bevel angle before buffing has to be lower than on an unbuffed blade, because buffing it increases the angle right at the edge. Before I started using the buffer on bevel-down plane blades, I used a 32 degree bevel angle. Now I use 25 degrees.

When you buff the blade, it must be done more lightly than for chisels and bevel-up plane blades. Too much and you lose clearance. But in order to buff the blade lightly and get a uniform edge, you need to make sure that there's a minimal burr left on the blade. If there's too much of a burr left on it, then the light buffing won't remove it cleanly, and you might end up with wavy edge like this:

442717

This will leave a surface that doesn't feel smooth.

This happened to me a few times before I figured out a way to deal with it. First I work the bevel side on a Shapton 1000, then I move to the Sigma 6000 and work the back lightly (so as not to tear off the burr), then do the bevel and then back again. When I work the back this time, I make sure put extra pressure near the edge, to make sure that the very edge gets abraded by the stone. (I won't get into it here, but the wear on the back of the blade near the edge can leave it slightly convex so that it doesn't contact the stone.) Working the bevel and back quickly one more time wouldn't hurt at this point. Remember, the goal here isn't to completely remove the scratches from the 1000 grit stone, but to cleanly remove the burr. Now, there may be some tiny residual burr left, but we just want to get it to the point where the buffer will leave a uniform edge.

Anyway, at this point, buff it, but less you would for a chisel or bevel-up plane blade. (There are many variables like type of buffing compound, how much buffing compound, pressure, etc, so I can't give an exact recommendation for how long, but after some practice, you get a feel for it and learn to see how large of a reflection to look for at the very edge.) The result is hopefully something like this:

442718

In terms of ease of sharpening, I was able to stop using my Shapton 12000, and I find that, for a really good edge, it's just easier and faster to do it with the method described above, compared to going all the way to the 12000 grit stone and being careful to do a good job with it.

This procedure may sound a bit complicated, but it really isn't, once you do it a few times. It may take a few tries to get the hang of it. By now I have it working solidly, every time.

Bear in mind that for bevel-down plane blades, buffing is not as advantageous as it is for chisels and BU plane blades. There is a benefit in terms of sharpness, smoothness, and ease of sharpening, but it doesn't really increase edge life, in my experience.


Oh, and to answer your original question, I don't think that the exact angle between the blade and buffing wheel matters. I've tried different angles and I don't think it makes that much of a difference, probably because the buffing wheel is so soft. Having the back of the blade approximately 45 degrees to the surface of the wheel seems to work. So with a 25 degree bevel, that would make the bevel angled about 20 degrees to the surface of the wheel.

[Mike Allen1010]

thanks Winston -super helpful!