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Sharpmaker idea: rods for convex edges?

Aug 11, 1999
Hi Sal and all,

Every few months, it appears, someone asks you if the Sharpmaker can be used to maintain, or create, convex edges. With the ceramic rods, not really; but would it be possible to design new rods for this purpose?

I imagine this would be possible with round rods comprised of a hard core and soft (leather or rubber?) surface sleeve, with pins or fasteners to securely affix pieces of SiC cloth paper wrapped around the soft surface. The idea is to provide a sharpening surface that "gives" a little, and therefore follows or creates a convex grind rather than flattens the face of the edge, as with current ceramic and diamond sharpeners.

I suggest leather and rubber simply as examples for the texture/characteristics needed in a surface sleeve. There are probably other synthetic materials to consider that can more effectively "give" or slightly yield to a harder surface (i.e., blade edge), yet remain resilient over extended use. This surface sleeve (1/8" thick?) may need to be replaceable.

I suppose a soft sleeve can be made to fit over the current ceramic rods. However, a round rod with a triangular heel to fit in the base is, I imagine, better than the triangular design for this purpose, as it allows for uniform tension across the whole surface. This would minimize tearing of the SiC cloth or other unequal wear, as well as allow for sharpening of recurved blades.

SiC paper is simply a suggestion, too; perhaps better abrasive wraps are available. In any case, SiC wraps or something similar would also allow for a wide range of grits, from highly abrasive to extremely fine. This might be a solution to the perennial "diamond sleeves" request, too. On the other end of the spectrum, one could, conceivably, even wrap around a piece of leather with jeweler’s rouge or stropping compound to final-polish the edge.

Okay, Sal & Co., now tell me what’s wrong with this idea and RRRIP IT APART! :)

My .02,

Why don't we try an adaptation of Schmackey's(Spelling from memory?)idea to test yours?

He posted Pictures showing SiC or similar paper clamped to the triangular rods.

Why not do the same thing with a soft backing as a prototype?

I will look around and see if I can come up with something and give it a try.
Yes, let us do that.

I've done this a bunch since then, and it works great. A cheap, fast, efficient solution.

As for convex edges...I bet we can adapt this idea with some makeshift parts.

In fact, I use a round wooden dowel (7/8" dia. x 11" long) with a piece of leather stapled to it, for sharpening convex edges. I wrap SiC paper around it, secured by binder clips; it works well for sharpening my khukuri, and I've used it to help shape convex edges on two other blades. Takes a while, but works. Fun "exercise" for knife knuts.

I haven't seen Schmackey's pic but have tried something similar. I used a three-layer "newspaper-leather-Sic" wrap around ceramic hones, fastened behind by binder clips. It worked fine, although not as well as on the wooden dowel for me. Partly due to its round surface, and partly due to its greater length, I think.

Anyhow, thanks for the reply; let's see what others think --


[Edit] Oop! Was typing as you were posting, Schmackey. Thanks for the link. You beat me to the idea, and with a nice pic, to boot! (All for an amazingly low $19.95 :))
This is a great idea! If we can come up with a simple method with parts that we can get all over the world and put up pics of the final device with instructions on building and use! That would be very very cool. I suggest we name ourselves the Convex Club or something like that;) ! I have been interested for a long time on wways to get a convex edge without a slack belt sander! Cool thread.
storyville -- a question, if I could please. It is based upon my total lack of mechanical aptitude and spatial concepts:
Would a flat arrangement work as well as your dowel? Is there an advantage to the curve the dowel presents?

One more: How much edge area can you work on at one time with your dowel arrangement?

Thanks in advance,
I was thinking about using an old Mouse pad as the backing and trying to configure it so that the flats and at least one triangle point is available as an option.

I need to get some different sheets of paper and select my test knives.
Bugs and others,

Wrapping leather or affixing hard rubber/foam to a flat surface, e.g., SDouglas’s mouse pad, should work fine. It would essentially function the same as a benchstone or sanding block ... and you can make it to *just* the right size for yourself! (Not too wide or narrow, not too short/long, etc. -- "custom benchstone," so to speak.) It’s really not complicated, and I say that as a pretty klutzy person. If I can do it, anyone can -- really.

I use a dowel because I originally wanted to maintain the convex grind on my khukuris, which have an aggressive forward-bending positive angle, or "recurve." A flat stone wouldn’t be able to sharpen the inside curve of the recurve, at least not as easily (e.g., you could use a corner, for example; but the SiC paper might wear away quickly or even tear). I also prefer the rounded surface because you can simply turn it slightly to get to a clean, unused portion of the abrasive surface, as the section you’re working with wears away. With a flat block, of course, you would wear away a larger contact surface less aggressively, which can provide for a slower, more controlled job.

Also, the dowel obviously provides less contact area than a flat stone or block, and essentially works like a thick steeling rod. The smaller contact area allows me to focus on a particular part of the edge that may need more attention, e.g., a "sweet spot" worn or damaged by chopping. Either way, rounded or flat surface, it should be easy to "adjust" angles along the same edge, e.g., slightly thicker edge profile at the sweet spot, and keener angle along the khukuri’s recurve and toward the handle for slicing. So it the difference -- flat or rounded -- also comes down to preference; it may be best to use both.

I should note that this isn’t my "genius" here; it derives from Cliff Stamp’s suggestions for convex sharpening, as well as others at the Himalayan Imports forum. Those guys are *truly* experts at this stuff.

Anyhow, two more cents --

Some interesting ideas. Also, nice pic Shmackey.

A convex edge is put on with a slack belt grinder (in America). Have any of you tried using a sanding/grinding belt clamped between two points, with "Slack" built in by not making it tight. Then use the belt by hand like using a stone. You probably wouldn't want to go much past the center of the arc. I don't know if than makes sense without a pic.

Hey Sal,

I haven't tried that, but it sounds similar to using a leather strop, barbershop style, yes? To compare and contrast approaches, maybe we could get some of the makers in Shoptalk to donate their used belts for the cause :)

I think the "method" we're proposing here is intended as an "easy to carry" and fairly idiot-proof alternative. The slack belt approach you suggest is probably much faster (and yes, putting on a convex grind takes a good long while), but sounds like it might require a higher level of skill (at least so it seems to me, the sharpening equivalent of "village idiot"). The leather (or rubber, hard foam, mouse pad, etc.) on hard backing offers a kind of "introductory" approach to the whole idea of applying a convex edge.

I'm hellishly busy at work right now, but will try to "rig" something for the Sharpmaker and give it a go over the next few weeks. Will "report back" my results when I get a chance --

I have used a wide leather belt with Chrome polish as a 'loose' strop, it gives very good results and possibly gives the convex edge Sal is refering to.
I finally went to the Hardware store and picked up some material for a Prototype and it seems to be working.

I picked up a combo pack of 3M Sanding sponges and some 3M emory cloth.

I cut the Sanding Sponges in half lenghtwise and clipped them to the Sharpmaker rods using 3 of the clips that Shmackey used.

The knife had a tendency to cut into the sponges so I covered them with the Emory Cloth and this is working very well.

I am using the 15 degree angles on my 204.
I will post my results when I finish.
I am pretty much finished sharpening an A.G. Russell ATS-34 Bird and Trout and a Camillus 154cm EDC.

Both knives are sharp enough to filet paper.

I don't have any magnification to say that they have a true convex edge but the process seems to work.