Convex sharpening help please

P

Plinthman

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Mar 30, 2008
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I have just bought a Fallkniven F1 which came very sharp. After a bit of use it is still quite sharp but will not easily slice through a piece of paper held in the air. Is this the right time to sharpen? I understand that it is harder to sharpen the duller it gets.
I have heard that a good method of sharpening convex grinds is with a mousepad and wet & dry paper, but I cant find much information on how to do this so I have a few questions:

1. What kind of mousemat: soft/firm/thick/thin?

2. What grits of wet & dry are needed (I currently own 600, 800 and 1200)?

3. How hard to I press on the blade while stropping?

4. How do I know when to move up to a finer grit?

5. What would be a typical amount of strops for each grit of paper?

6. Can I bugger up the knife if I do it wrong? should I practice on a cheap knife first?
 
what Esav said

I'd like to add that it sounds like a little touch up on a ceramic stick will be enough for now. I can reccomend the Sharpmaker for this.
After a couple of touching ups like this you will be starting to form a V grind on your edge, and when that becomes clearly visible to the eye, then it's time to knock the shoulder off, and smoothen the edge convex again. The mousemat/sandingpaper is a very effective technique then.

Take it easy on the grit. Better 10 passes extra on a fine grit, then 1 pass to much on a rough grit.
 
Martin Swinkels said:
Take it easy on the grit. Better 10 passes extra on a fine grit, then 1 pass to much on a rough grit.
Click to expand...

This is very important, and something we don't mention often enough. Sharpening of any kind should always be done gently, just brushing the blade across the medium. Don't be in a rush to remove steel! :)

My personal technique for touching up a convex edge is to take a fine ceramic stone and strop the edge across it with a turning wrist, to keep it convex rather than v ground. But this sort of action comes with experience. 40 degrees on the Sharpmaker may very well restore the razor edge on your F1 with just a few passes.
 
Leather strop. Bark River black and green compounds. All you need. Stay away from the crock sticks etc.
 
Martin Swinkels said:
what Esav said

I'd like to add that it sounds like a little touch up on a ceramic stick will be enough for now. I can reccomend the Sharpmaker for this.
After a couple of touching ups like this you will be starting to form a V grind on your edge, and when that becomes clearly visible to the eye, then it's time to knock the shoulder off, and smoothen the edge convex again. The mousemat/sandingpaper is a very effective technique then.

Take it easy on the grit. Better 10 passes extra on a fine grit, then 1 pass to much on a rough grit.
Click to expand...

So you are saying it's easier/better if you give it a flat (V) grind first, then the convex edge is easier to create? Would that give you more of a flat grind with convex bevel rather than full primary convex? Does it even matter if your primary is a flat grind or convex? I don't have any experience with convex, so I'm in the dark.
 
Here's my setup. 7-8oz leather glued to hardwood or MDF. Then, wet/dry taped to the leather. I rarely go below the 1000 grit, most of my sharpening (or, maintaining a sharp edge) is done on the 1500 and 2000.

One side:
convex-01.jpg


The same "strops" flipped over:
convex-02.jpg


I generally strop about 10 times one way, then 10 the other. Then I'll go about 5 and 5. Then back and forth a couple of times, once on each facing of the blade. Then strop with leather and green compound (or lately, the white).

Go to Esav's link for "sharpening the BRKT way". THat's the way I learned. After a time, you'll develop your own technique and feel for it.
 
heelflip_kid said:
So you are saying it's easier/better if you give it a flat (V) grind first, then the convex edge is easier to create? Would that give you more of a flat grind with convex bevel rather than full primary convex? Does it even matter if your primary is a flat grind or convex? I don't have any experience with convex, so I'm in the dark.
Click to expand...

It's easier for sure.
If you want to keep edge geometrie the same as it was n.i.b. you 'll have to work the whole grind with each sharpening.
 
Esav Benyamin said:
My personal technique for touching up a convex edge is to take a fine ceramic stone and strop the edge across it with a turning wrist, to keep it convex rather than v ground.
Click to expand...
Do you have further instructions on convex sharpening with a hard stone, or any info you can refer me to about this subject? I've tried it myself and have not been successful, but would like to learn.

Thanks!
 
db--

Thanks for your reply and the link.

I never got good convex edges with the mousepad/sandpaper method, either, so thought I'd try a stone. I get good edges with a low-angle relief grind and microbevel, but would also like to learn to convex sharpen. Most of my knife use is in the wilderness so I need to keep things as simple and lightweight as possible. It's a lot easier and less bulky for me to carry one stone than it is to carry around a mousepad and a lot of sandpaper in different grits.

Maybe I'm missing something, but my understanding is that once you raise a burr you are at the extreme edge and can't get the knife any sharper, except by lowering the angle, which you are not doing in this case. I don't understand what you are accomplishing by continuing to raise a burr with finer grits, except maybe polishing the edge a bit.

Also, how are you getting a convex edge by holding the edge flat to the stone? I would think this would put on a flat "V" edge, not a slightly rounded convex edge.

Thanks..........
 
Good questions. 1st by scrubbing back and forth quickly my natural motion produces a rocking motion that will give you a convex edge bevel. You can ajust this to how much of a curve you want by how much you rock the blade. personally I don't pay to much attention to how much I rock I just scrub away and try and keep both sides fairly even and centered. I mainly check for how much of a angle I want and never raise the spine up higher than that. then I will rock the blade down as low as it can go if I want a full blade with convex grind. So scrubbing from flat to the stone up to the spine raised only as high as you want your edge angle is a full convex grind but you can do any amount you want from very little rocking, just remove the shoulder, to a full grind. Heck if you want you can even micro convex edge bevel on a full convex grind, or really any combo of curve or thinning you want or need.Now you sure don't have to raise a burr at every grit level, in fact once you get the hang of sharpening this way you don't ever have to raise a burr. It is just easier to learn to do it and for me to explain it in writeing by the burr method. Now my finishing strokes are all edge forward with a light touch and kind of a scooping motion alternating sides. It really is much easier than it sounds.
 
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"I don't understand what you are accomplishing by continuing to raise a burr with finer grits, except maybe polishing the edge a bit."


exactly. all you are doing is polishing the edge so that it will in theory push cut better. if you want to draw cut more, then just break the burr by stropping or skipping several grits to a very very fine abrasive from a courser grit.
 
db--

Thanks for your reply. I learned to sharpen this way from The Razor Edge Book of Sharpening, by John Juranitch, but I had no idea before now that this put a convex edge on a blade. I was quite surprised and am glad the subject came up, as this is interesting knowledge.

Usually I raise a burr by using small circular motions, since this is easiest for me, but I'll try the "back and forth" method you describe. Just a couple of questions, if you don't mind: I assume the back and forth movement is at a right angle to the edge, and not along it? Also, I'm not sure what you mean by "rocking". Do you mean slightly and constantly raising and lowering the spine when forming a burr, or another kind of motion?

I'm not real good at visualizing from words and want to be sure I know what you mean. Thanks!

siguy--

Thanks for confirming I am on the right track with my thinking.
 
Yes to both of your questions. Circular strokes should work just as well as my scrubbing motion. In fact when your just shapening or raiseing a burr the stroke you use shouldn't matter . I really don't even think about the rocking motion as I sharpen. Maybe another way to describe it is a sloppy hold, don't even try to keep to a angle just let the sharpening stroke do its thing I think it is pretty hard not to get a convexed bevel free hand unless your really good at holding an angle and keeping to that angle for every stroke every time you sharpen..
 
db--

Got it! :D

Thanks a lot for the instructions and clarifications. I have learned much from your posts on this and other threads. :thumbup:

jonnyfgroove--

Glad you are learning and laughing. :) As you can see, there are several knowledgeable people on this forum who graciously share their knowledge with others.
 
Since there arn't many cheap covex blades about, would be ok to practice on an old SAK that I have? I know these dont have a convex edge, but wouldn't the mousepad technique create one? Don't really want to ruin my F1.
 
Yes it is ok. In fact I convexed all my SAKs and prefer them convexed. A Vic SAK is a pretty thin blade and is fairly easy to put a shallow convex bevel on. Go for it.
 
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