What’s soft stuff – stainless steels that roll without chipping (cheap pocket knives), old irons that are really low on the hardness side almost tending toward saw hardness, and so on.
When I rolled out the unicorn method, it was something to me in terms of value because it created a situation where mediocre or not quite ideally set up tools would hold up well. The first use in my case was incannel patternmaker’s gouges. I’ve since learned to sharpen them quickly, even reprofiling one that’s ragged is not more than a matter of three or four minutes from start to finish, and then they’re in shape forever. They are usually reasonably hard, but it’s not hard to chip them.
The second thing that became obvious was tools that seemed almost unusable could be used, which for me at the same time, was an SG2 pocket knife (Fallknaven) that would absolutely not sharpen on regular stones. You could sharpen it, and feel sort of a grabbing feeling on synthetic stones and it never seemed sharp. That was actually carbides breaking out of the apex and a look at the edge under a microscope would show what looked like pitting where the carbides broke out of. I don’t know the composition of SG2 off of the top of my head, but I’ll bet it has vanadium in it. Whatever the case, it had carbide coarseness.
The buffer made that usable and then proceeded to make every softer knife and tool that I have usable to some degree, and then prove easily that a standard plane iron would far outdo V11 or 65 hardness M2 in knotty or dirty wood or exotic woods with silica. It wasn’t the wear knocking tools out, it was deformation of the apex and the question only becomes after that whether or not a tool is so soft that stopping deformation basically results in a blunt tool. Put differently, if the apex deforms and the steel has great edge stability and hardness, it doesn’t take much. You still have a thin edge. If the steel is tending toward very soft, you have to either steepen or round off the apex more and the worst of the worst will still cut, but feel a little dull.
I don’t have that many soft tools, but a typical mid to high 50s item floating around is inexpensive pocket knives or typical buck 420hc folders. if you sharpen a buck folder 15 degrees per side, and strop off the burr, you’ll never really get the whole burr off and the edge will dent in just about anything, and roll. The steel is super tough, though, and with the apex modified, it’s fast to sharpen, lasts longer than you’d expect and is “sharp enough” for almost anything. With a little extra modification, those buck knives will actually scrape brass without rolling.
Defining the Problem
There are a few things you have to consider before you apply a method if you want a cheap knife to be sharp:
- if it’s stainless, it will probably be something fine grained and soft (not coarse, as the rumor will often be). Why? The softer steels are generally lower in carbon and simple to allow for simple heat treatment. No big carbides, no carbides to coarsen. This is usually achieved by keeping the carbon content low, and thus the hardness will be relatively lower.
- if you have a soft blade, then abrasives that seemed marginal will suddenly cut very quickly and harshly. Remember that the silica and transformed silica type abrasives like novaculite are about the same hardness as hard tempered martensite. This is why they can have relatively large particles but cut very finely – the abrasive cannot plow a row like diamond would. Drop the hardness from, say, 63 down to 55 and suddenly the cutting action is brash
- if you have a knife blade that is drop point in style or something else with a small contact area, the effect is magnified further as the pressure of sharpening is concentrated.
- Even if you can sharpen a very fine apex ( you can ) , the apex won’t have the stability to hold up. I envision people with those alien arm thingies with little stones on the end telescoping in and out spending 20 minutes on a blade to create a very fine apex, shaving hair and then finding the edge has rolled 20 seconds into actual use.
Solving the problem
You need to set the edge geometry in a way that it will hold up. I personally still prefer treating the bevel and apex separately. That means even on cheap knives, sharpening at a relatively low angle on a synthetic oilstone (use whatever you want) because it’s quick, and then addressing the apex either with a buffer or with compound on a backer that isn’t any harder than MDF. if you use a really hard substrate, you can actually roll the apex itself while sharpening.
And, of course, the buffer does all kinds of things abrading gently and rounding the apex at once. It takes the skill out of doing this and is really hard to even match. The next time you have to do significant sharpening, you can set the bevel again to remove most or all of the buffed portion and then buff again and have a very strong apex. If you do it right, even very soft blades will shave cleanly and cut paper easily on both sides of the bevel.
Just be careful that with knives, your fingers aren’t below the blade, and anything that looks like a point gets introduced to the buffing wheel pointing somewhat in the direction of rotation. Never bevel up into the wheel and never hands under the blade (this means probably no slipjoint knives unless you can hold them in a way that they won’t snap shut on fingers. I’m not going to say I don’t buff them, because I do, but it’s a little less easy to figure out).
Abrasive vs. Backer
It’s easy to understand why the buffer works gently, even with aggressive abrasive. But maybe less easy to understand just how big of a difference substrate can make with typical alumina compounds – like those in a buffing bar. It’s easy for me to relay what I’ve seen, but maybe easier for you to see for yourself. Put sandpaper in a hard sanding block and sand something with it. Then, put it on a loose rag and try to generate the same volume of dust.
This gives us the ability to use something like soft white pine as a final step, but a relatively aggressive finish abrasive, like a 5 micron yellow bar, and get an edge that’s more like a 1 micron edge. And because the treatment at the very edge is also less of a threat in deflecting the edge itself, there will be less of a burr for two reasons.
Simply put, you have two ways to deal with soft steel – a softer abrasive (or finer), or mitigating the effect of a common abrasive like alumina by finishing the edge on a softer backing. Like finishing a soft pocket knife by drawing it backwards on white pine instead of push sharpening in a stone. And round it over just a bit at the tip.
Almost everything worth doing in woodworking is a matter of touch/feel and developing skill. But as complicated as this is to discuss, if you were in my filthy shop, you’d be surprised how little there is to it, and how easily you can develop that feel and discretion. It is the universal fertilizer of capability to use that to solve problems rather than looking for expensive solutions like a new knife that’s better than your current knife, but worse than your current knife with sharpened properly.
How do you know you’ve got it right? Sharpness – I think box cutting for your recyclables or burn barrel is a good way to find out. A very soft knife with a fine apex will actually roll or deflect in the corners of coarse cardboard. that same exercise will also show you how much better a knife with a thinner bevel and adjusted apex is than just increasing the wedge angle of the whole knife to avoid damage.
If I can use a buck knife to chamfer the inside of a brass ferrule and see no damage to the edge, you can, too.
You don’t have to figure that you’ll nail it on the first try. if the knife seems too dull, less adjustment. If it rolls, more. The better the knife, the more latitude you have to work. I keep saying knives because tools this soft are uncommon and sharpening a pocket knife *well* (which is a treat) is less common. But apply it to tools if you have some one off tool that just won’t hold an edge in your work. Maybe it actually will if it’s accommodated. A truly defective tool is only one that’s so bad that it can’t be accommodated at all.
Of Making by Hand with Wood and Steel 