this post was submitted on 28 Jul 2024
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Tips/Tools for sharpening a recurved blade? (fedia.io)
submitted 3 months ago by [email protected] to c/pocketknife
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Hey guys! I've just recently gotten into collecting pocket knives, and I wanna make sure I'm taking proper care of them. My last two purchases have been karambits, both with fairly steep recurved blades, whose edges I'd like to be able to maintain.

I know that normal sharpening stones aren't going to allow me enough contact with the blade to actually put an edge on it, so I've picked up a Smith's DRET sharpener and have been practicing on an old dull knife with a stiletto blade, just to try to get some basics down. I'm getting better with it, but I'm struggling to get an even, consistent edge. Even without any special optics, I can see with my own eyes that I've got wildly uneven angles.

Granted, I'm practicing with a very low-quality knife that was already in pretty rough shape. I've managed to get the edge from "literally unable to break the skin with 20 pounds of pressure and aggressive sawing motions on my forearm" to "can cut through paper with about half of the blade before bunching up", though it's come at a cost of scratching the absolute hell out of the rest of the blade (which is just me being sloppy).

I figure that once I'm able to get competent enough with sharpening a normal blade shape that I'll move on to testing with a donor karambit. I picked up a super cheap, mall-ninja-ass karambit on Amazon because the reviews were all poor and said that the knife arrived completely dull, so I figured this would be perfect to practice sharpening. Unfortunately, it arrived with a surprisingly sharp edge, so I'm gonna have to abuse this knife for a bit before I can even practice anything on it.

Just curious what sort of tools y'all recommend for dealing with recurved blades, or any techniques I could try to incorporate into my practicing. Thanks!

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[–] dual_sport_dork 4 points 3 months ago

I don't know about the "right" way, but what's always worked best for me on this type of thing are round sharpening rods. So I think you're on the right track with the DRET and its round profile.

As always, the key is keeping a consistent angle between the sharpening stone and the knife. Free hand sharpening with a round rod is even harder than with a flat stone. You might think about setting up some manner of angle jig. If it were me, I'd steal the idea from the Spyderco Sharpmaker: Make some manner of jig that holds the rod at a specified angle, and move the knife down along it holding it precisely vertical rather than trying to move the stone. Come to think of it, the rounded corners of the Sharpmaker's stones would probably work pretty well for that task also.

If you want to educate and/or annoy yourself, grab a cheap linen magnifier from the internet. You can easily inspect your edge geometry up close with one of those and see if you're hitting the correct angle, if you've rolled the edge, where any inconsistencies are, etc.

[–] [email protected] 2 points 3 months ago (1 children)

Recurve blades are my favorite profile, so I've spent a lot of time sharpening them. Any sharpener that has a relatively narrow edge will work. Round rods, as mentioned here, are a good choice. The Spyderco Sharpmaker comes with triangular rods that are perfect for this. As long as your sharpener has a radius less than the curve of you blade it should do a good job.

One of the most effective sharpeners for curves are those small crossed stick sharpeners. Avoid using carbide sharpeners, but ceramic or diamond dust work well. Here's my favorite of this type: https://www.amazon.com/gp/product/B00AU6CM2I/ref=ppx_yo_dt_b_search_asin_title?ie=UTF8&th=1

Best of luck!

[–] [email protected] 2 points 3 months ago (2 children)

Thanks, I was also eyeing the Sharpmaker, but I'll check this out, too! I was always under the impression that pull-through sharpeners were bad for edge retention since it leaves scratches parallel to the edge; have you had any issues with yours maintaining an edge?

[–] [email protected] 2 points 3 months ago

I think the problems with pull-through sharpeners are almost all related to the common use of carbide sticks for the rough sharpening. Carbide basically tears off chunks of metal instead of abrading it smoothly. That can do real damage to the edge.

I've gotten excellent edge retention with that particular pull-through sharpener. I have looked at the result of both stages under a serious magnifier without finding any tears or scratches. The main limitation is that you're stuck with the default angle.

Something like the Sharpmaker gives you more control. It's great for things like re-profiling or setting a secondary bevel. It also gives you a choice of angle.

[–] godot 1 points 3 months ago* (last edited 3 months ago)

Scratch patterns are in my experience a little overblown, particularly at high degrees of polish. The sharpener they linked you finishes on ceramic, which generally is fairly fine.

Pull through sharpeners’ biggest problem is that they can’t practically get a clean, consistent apex that follows the sweep of the edge. To get close the housing of the sharpening material needs to be extremely rigid, the pressure used needs to be consistent and light, the angle of the knife in the sharpener needs to be consistent from pull to pull, and the sharpening material needs to be very clean. Otherwise the act of sharpening, while perhaps polishing the bevel, drives the apex into steel residue or abrasive or shifts its angle. That will round, grind down, or rip tiny chunks out of the apex. Still gets a pretty sharp edge.

I don’t find pull throughs suffer much with regard to retention. They don’t get a knife as sharp initially, so they do start with a shorter clock. But from there retention is okay. They completely avoid wire edges, which is nice, so in inexperienced hands in a way they much improve retention.

For most knife steels and uses, pull through sharpeners are okay when used with a light hand. What I’m calling a “clean, consistent apex” isn’t practically necessary in pocket knives. The Sharpmaker and several cheap jigs can produce edges like that, though, and those edges definitely feel better in use. At the reasonable additional cost that’s worth it to a lot of people.

[–] godot 2 points 3 months ago

It is possible to sharpen a recurve edge on a waterstone with a rounded corner, but having wasted my time learning how I prefer the Sharpmaker. It’s near enough to the same speed, more intuitive, and more difficult for a new sharpener to make a mistake.

Some jigs have rounded stones specifically for recurves; I know there is a Lansky set. I haven’t used one, myself.

I suspect almost all heavy use recurve blades, carpet knives come to mind, are sharpened using pull through sharpeners. There are shaped sharpening stones specifically for recurves historically used in trade work, but they’re going to kind of suck.

Perhaps not a useful avenue for you right now, but my best results on recurves have by far been from paper wheels.

I know you asked how, but if you end up with only a few recurves paying a pro to do it is a reasonable option. Sharpening recurves is a niche inside a niche. No method I’ve tried of doing it by hand feels elegant or “right”.