Thread: The Unicorn method

Originally Posted by derekcohen

I invested in another half speed bench grinder,

Derek, I'm curious about the benefit you feel a slow speed grinder gives in this situation.

Originally Posted by D.W.

It works fine on all irons. Here is a picture taken through a solid cherry shaving off of a cambered smoother iron (gradual camber along the entire iron, I don't nip corners).

https://i.imgur.com/nuk3Q0a.jpg

The iron used in this case was $2.99.

In terms of getting things right, it's more about not doing too many things than it is doing anything complicated right. Very shallow primary. Slightly less shallow secondary and then a couple of even passes along a buff that's got give at the surface but some backbone underneath.

While it's fast on a plane iron, I don't think (other than bevel up irons) it has as much to offer except when trying to get a good finish on an iron that's so cheap and soft that it's hard to really finish the edge by hand (or on an iron that is so soft that an unmodified apex can't really hold up to hardwoods. This iron is one that won't tolerate much if sharpened, let's say, to 32 degrees final bevel off of one of the finest shapton stones. The apex gets deflected easily and can even be bent when stropping. Take it away and it's fine.

So fine that it will plane cocobolo with visible shiny silica particles without taking a dent.

That initial edge stoutness is what makes it good for all chisels (debatably a little less so on mortise chisels, though, if you're going to pry so hard that you bend the bevel above the unicorn - it's nice to have a bit stouter bevel on a mortise chisel to ride, also, as a very thin bevel can be a bit awkward on bevel down riding except in really deep mortises (thus some pigstickers having something relatively similar).

But, folks having trouble, I think are doing too much, or not getting the prep right. It should be 30 seconds of not much effort for a chisel and then you can mallet with a chisel long enough for it to get so warm that you can melt a crayon with it - and keep going. Nobody's shoulder can take all of the work in a straight line to outlast the edge. I sure can't.

David; whats the likelyhood of overdoing the buffing and loosing clearance at the cutting edge on their bevel down plane irons.

regards Stewie;

Originally Posted by planemaker

Hi Derek; a little curious as to why buffing a bench plane iron will create an uneven edge, but it doesnt become a factor when applied to a block plane iron.

Is it because theirs no camber on a block plane iron. j

regards Stewie;

Hi Stewie

The camber is the primary issue for me, notably for BD smoothers. The issue is controlling the amount of camber. A second issue is with BU planes (not block planes), where the secondary bevel dictates the cutting angle.

I have not spent much time on plane blades, so it may just be more practice is needed.

Regards from Perth

Derek

Originally Posted by tony_A

Derek, I'm curious about the benefit you feel a slow speed grinder gives in this situation.

Tony, I use what I am used to. Plus I am keeping my options open. My primary, CBN-equipped bench grinder is a half-speed model. One can work nearly as well on a full speed grinder. However, a slower speed offers a little more time before you screw up.

Regards from Perth

Derek

Originally Posted by derekcohen

Hi Stewie

The camber is the primary issue for me, notably for BD smoothers. The issue is controlling the amount of camber. A second issue is with BU planes (not block planes), where the secondary bevel dictates the cutting angle.

I have not spent much time on plane blades, so it may just be more practice is needed.

Regards from Perth

Derek

Thanks Derek ; appreciate the feedback. I currently restrict the buffing wheel to my carving chisels and gauges. But my own understanding within its restricted use is that it doesnt take much to overdo the buffing and end up with too much deformation or rounding on the back of the cutting edge. Hense the question to David on the likelyhood of loosing clearance at the cutting edge on bevel down plane irons.

regards Stewie;

Stewie, overdoing the buffing is a main reason to use the loose cloth wheel or mop, and not something hard or firm.

I suggested elsewhere that one should not think of the process as stropping, but rather as mopping.

Regards from Perth

Derek

Originally Posted by derekcohen

Stewie, overdoing the buffing is a main reason to use the loose cloth wheel or mop, and not something hard or firm.

I suggested elsewhere that one should not think of the process as stropping, but rather as mopping.

Regards from Perth

Derek

A "mopping up" operation? Send in the cleaners. (I may have watched too many movies ).

On a more serious note I am still working up the courage to try this.

Regards
Paul

Originally Posted by planemaker

Thanks Derek ; appreciate the feedback. I currently restrict the buffing wheel to my carving chisels and gauges. But my own understanding within its restricted use is that it doesnt take much to overdo the buffing and end up with too much deformation or rounding on the back of the cutting edge. Hense the question to David on the likelyhood of loosing clearance at the cutting edge on bevel down plane irons.

regards Stewie;

separately - if there's a desire to use it and there's a concern of lost clearance on a bevel down plane, the solution is relatively simple.

reduce the angle of the steel that's introduced to the buffer and then just buff both sides of the bevel closer to tangent to the wheel.

For example, if you find success with a 32 or 33 degree flat bevel and get good clean edges for a long time (as in, no unexpected nicking, etc), introduce an edge that's 5 or 8 degrees more acute. You'll end up with something close.

There are things that you can do to game slower abrasion - like getting a truly fine buffing compound, lighter touch or less compound on the wheel (I think the former two are more useful).

The reason this works is that a bevel (above the very edge) at 25 survives planing just fine. The last couple of thousandths with a 25 degree bevel does not (the damage I"ve seen under the scope with most chisels and plane irons goes between 2 and 4 thousandths. 2 thousandths of intermittent damage to an edge is enough cause a plane to cease entering a cut no matter how heavy handed one wants to be. A smaller section of slightly larger damage just in one spot can do the same - the steel deflects and creates a blunt foil that won't enter the cut.


*if* one takes an already honed iron at a typical finish angle to the buffer and then buffs it, the final angle will be much more and the outcome predictably poor. We (most of us) have in our heads that if we modify the tip of an iron for the last couple of thousandths but leave a thin bevel above that, that we'll make a bevel that deflects - but it doesn't happen. Not even when planing cocobolo. I chanced into this by recovering a very old wooden plane once with an enormously thin long bevel, and a tiny microbevel on it, I thought about grinding it back (for sure, I'd break bits of the edge off). Instead, I used it. The primary bevel was 20 degrees or less - to the point of looking bizarre. I can only guess that someone in the distant past had access to a large diameter silica grindstone (it hadn't been ground with anything modern) and took advantage of the fact that they could just refresh a much smaller bevel a few time and have excellent clearance and sharpening speed. The bevel was so shallow and flat that it would've been difficult to do freehand on a flat grindstone and was probably done on a large diameter wheel.

Originally Posted by Bushmiller

I am still working up the courage to try this.

It definitely works although I'm still finessing my technique. Try it on a chisel.

A bit off topic Derek but I noticed you have a Rikon half speed bench grinder . From your post I know you generally appreciate quality tools . What are your experiences with these ? I am looking for a bench grinder and I am not happy at what I have seen in Bunnings , the price looks OK .

Originally Posted by pianoman

A bit off topic Derek but I noticed you have a Rikon half speed bench grinder . From your post I know you generally appreciate quality tools . What are your experiences with these ? I am looking for a bench grinder and I am not happy at what I have seen in Bunnings , the price looks OK .

The Rikon is a very good bench grinder. There is NOTHING at Bunnies that is remotely in the same class. Frankly, it is probably the only half-speed 8" grinder available in Oz.

If you can afford the Rikon, I would recommend it.

Regards from Perth

Derek

f I get this right, I can follow whatever my sharpening ritual is for chisels, planes, (even kitchen knives?) and then add this step to round over the edge with a buffing wheel?

well, I'd shorten the ritual prior to the buffer, and make the bevel a little more acute. For example, if you grind at 25, then just hone some with a medium stone at 25 degrees and then buff relatively briskly (you'll have to experiment to get the feel, but once you've got it, you've got it).

That would be as an alternative to something like a final microbevel at 32 degrees instead.

I think some folks have trouble with this method for planes though (you can see from the videos that I don't find it much trouble, but I intended it for chisels and only worked up a method with plane irons because some folks on another forum suggested that honing on stones freehand isn't always easy for everyone - the resistance of the edge to damage from silica was just a nice side surprise).

So for plane blades, my irons have a 25deg default primary bevel, and I put a 30deg secondary bevel on by sharpening freehand (have had no issues with this). Would you suggest using this method on the 30deg secondary bevel, make the secondary bevel a bit lower, or just do this straight off the primary bevel?

Also, I'm assuming that you wouldn't do this for bevel up planes because it changes the angle? Not that I have bevel up planes at this moment

You may have already done a video on this - I haven't searched it up yet. I will do so