Convex sharpening - What am I missing?

F

Flanker

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Oct 28, 2007
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In my knife drawer there are a few Spyderco folders, a couple of Ontario Rat's and a Helle of some sort. What they all have in common is a shaving sharp edge, thanks to my Spyderco Sharpmaker (man, I love that thing). But next to them lay two convex blades, a BRKT Northstar and a Fallkniven F1 that aren't feeling too good.

I've tried a mousepad with 1200 wet/dry paper and some cardboard (don't have a proper strop yet) loaded with both black and green compound. All used patiently with the edge at 12-15 degrees, trailing the edge and using light pressure. I just can't get these things as sharp as I'd like, and it's annoying me. They're not extremely dull or anything, just not sharp enough! I seem to get them to an ok "utility edge" but no further.

I've watched YouTube videos of this stuff, and can't see any flaws in my technique. Any tips before I go mad and sell two of my best knives here? Isn't 1200 grit coarse enough? Or is the covex edge just not for me? *sniff*
 
i think that if they aren't sharpening up then you should try going down to like a 600 grit paper and working up to 1200 grit.

the cardboard is fine, its what i used for a year before i realized i could chop up an old belt for leather.

also, try coloring in the edge area on both sides of the blade with a sharpie marker and making a couple of passes. this will tell you if you are actually hitting the edge or just polishing the sides of the knife. if you aren't hitting the edge, try raising the knife a few degrees at a time until you see that you are hitting the edge, then keep sharpening at that angle.
 
Are you actually hitting the edge? Try the Sharpie trick to be sure. Since the convex edge continues to curve "in" all the way to the edge, the final angle can be "wider" than you might think.
 
I like that trick with the sharpie Siguy.

I had the same problem, I got the BRKT strop and I can get my blades sharp now. I am still going to give that marker thing a try, as I can improve.
 
Are you "rolling" the knife as you draw it across the sharpening medium? Try increasing your angle slightly as you finish each pass.

Most freehand sharpened knives (except the so-called "Scandi's") have a convex edge due to variations in how the knife is held.
 
i had the same problem trying to convex an old kabar bowie blade a put a handle on. I started at 320 and went 400 and then 600. I just couldnt get it as sharp as i wanted. So i tried the sharpie trick and realized that i wasnt always removing material from the edge, so i picked the blade up a few degrees and now i'm starting to get somehwere.
Even if you have to paint the edge every 20 strokes to get it right thats ok. Eventually you'll get it. Also i believe that the Northstar and the F1 are tool steel, so it will take a little while longer than it would with a lot of other blades.

Since the blades in question are already convexed i wouldnt go down to 320, but maybe 600 would be a good starting point. And remember not to push too hard :)
Hope that helps.
Chris
 
Three things to know about convex sharpening. Maybe four.

1. It seems to take everybody (even folks who have been VERY good at getting a razor-sharp V edge, for decades) a VERY long time to get the hang of convex sharpening. It took me several hours to learn, and the first several knives I tried to sharpen that way, I gave up on. It did FINALLY come. So, don't go selling your dull convex knives yet. (Or, if you do, sell them to me, for a fire-sale price!)

2. The Sharpie technique is VERY helpful. Lets you know when you're actually sharpening the edge, and when you're removing steel from less-relevant areas.

3. One thing that some people find helpful is to put a layer of something soft--e.g., a strip cut out of a computer mouse pad--under the sandpaper, on top of whatever hard, flat surface you're using for your strop. I use a paint-stirring stick, the long kind.

4. Bear in mind that the initial sharpening using a convex sharpener may take more time than usual, because you may have to remove a pretty decent bit of steel from the whole region just spineward of the edge, in order to get the very edge genuinely sharp. You might get faster results by putting a good, sharp V-edge onto it, and then doing your convex sharpening. This way, you may be focusing your sharpening efforts onto the shoulders of the V-shaped edge bevel, and you can gradually convex the already-existing V-shaped sharp edge.

Don't sweat it. It takes everybody a long time to learn; it's not just you, nor your knives. It's kind of like learning ancient Greek--everybody I know who's done it really didn't get it "down" the first try, but had to keep working at it. Convex edges are the same way--and a wicked-sharp convex edge is truly a sight to behold in a woods knife. Good luck!
 
Will try the sharpie trick tomorrow and see how it goes. I'll update then. Thanks so far :-)
 
Also, be sure you aren't pressing down too hard. If you press too hard, you can actually be dulling the edge rather than sharpening it.
 
Very lightly push the blade forward, edge leading, from flat on the strop to where it starts to catch. That is your bevel angle, continue stroping (edge trailing) at this angle until happy, satisfied, pissed or whatever. This has worked for me,

Shane
 
I'm impatient. I do my edges on the belt sander. It took me a while to get the feel for it...and I'm still learning....but David Farmer gave me some good tips that let me get a shaving edge pretty easily.

Scott Gossman and Dan Koster have some good tips and videos on convexing IIRC.
 
Ok guys... I finally got it right! Tried the sharpie trick, and there was nothing wrong with my angle. Turns out I was applying too much pressure. Just holding the knife and letting its own weight do the work turned out great. My Northstar now has a razor edge again :)

Now I'm working on my Valiant Golok - It's a bit worse, but I'm getting there.
 
Flanker said:
Ok guys... I finally got it right! Tried the sharpie trick, and there was nothing wrong with my angle. Turns out I was applying too much pressure. Just holding the knife and letting its own weight do the work turned out great. My Northstar now has a razor edge again :)

Now I'm working on my Valiant Golok - It's a bit worse, but I'm getting there.
Click to expand...

When I have a convex edge that does not feel sharp, the first thing I do is take several light strokes on a 12" ceramic rod. I start well back from the edge and approach carefully. You can feel the edge when you get there. If the blade has a good profile this is usually enough.

If the ceramic rod doesn't work it means the edge is too thick and you will need to re-profile a bit. I'm lazy like bruche, so, if the edge is way too thick I'll use a belt sander; start coarse and work up to fine. If the edge is only a little too thick I just use a large DMT diamond bench sharpener. Usually I start with coarse and work back to fine. I've used this technique to get a finer edge on my Northstar and Aurora.

I'm surprised to hear you have a Valiant golok that is not sharp enough. Try a large ceramic rod first. Use it just like you were sharpening a carver with a butchers steel. It's easier to hold a constant angle on a large blade with a rod than with any other sharpening implement (short of a belt sander).
 
Well, the Valiant is now razor sharp too. It was sharp, but not THAT sharp out of the box. Just got it today, it's a 10" Golok Jagal... It was a pain in the ass doing it on a mousepad with 1200 grit wet/dry but I nailed it in the end! On a large blade like my 10" golok you can actually hear when your hitting the edge correctly. The sound of the blade against the sandpaper changes pitch just a little bit. Anyone else experienced this?

Will try sharpening it with ceramic rods or my pen-like diamond hone next time it needs a touchup. Thanks for the tip, HighDesertWalker.
 
Flanker said:
Well, the Valiant is now razor sharp too. It was sharp, but not THAT sharp out of the box. Just got it today, it's a 10" Golok Jagal... It was a pain in the ass doing it on a mousepad with 1200 grit wet/dry but I nailed it in the end! On a large blade like my 10" golok you can actually hear when your hitting the edge correctly. The sound of the blade against the sandpaper changes pitch just a little bit. Anyone else experienced this?

Will try sharpening it with ceramic rods or my pen-like diamond hone next time it needs a touchup. Thanks for the tip, HighDesertWalker.
Click to expand...


Glad that worked out for you. I should have mentioned that a ceramic rod is the best big blade touch up tool I've ever found. When I'm working in the yard (pruning, etc.) I carry one along. Just a few strokes every 20 minutes or so keeps a blade razor sharp. :)
 
Cheeeezus... Tell me about it! I grabbed the fine grit rod from my Spyderco Sharpmaker, just to try a finishing touch on the Valiant. Dear god, it's the sharpest thing ever! I'm grinning like an idiot here :D

Now I just need to get me a leather strop and make a hoodoo hone for field sharpening of the F1 and Northstar. Thank you HDW, I think that's the best tip I've gotten so far on these forums
 
My guess would be that you're not lifting straight up at the end of the stroke and was dragging the edge on the stone ever so slightly.
 
Unless I'm just touching up an edge, I start with 220 grit sandpaper. OOOOOOO. Big whup. Your sharpmaker is taking off a fine sliver of metal over a small area. You're trying to reconvex something down to a zero edge if you're goin at 12 degrees. Thats a fair bit of metal to remove, and you're using 1200 grit paper. Those knives are just laughing at you. It'd be like building the sears tower with tweezers.

Start with 220 grit, go to 400 grit, then 600, then your 1200. (I never go past 400 grit.)

Cardboard makes the best strop I've ever used hands down. Nothing removes a burr as fast as plain old cardboard without loading it with anything at all.
 
Does anyone here offer sharpening on Convex edges. I do fine on all the other edges but struggle with the convex. I too just picked up a new F-1. It's sharp as hell now but that may not last long.;)
 
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