Need some Tips: Convex Sharpening

You could well be applying too much pressure. Perhaps counter intuitively I think it is easier to dull the edge as you seem to have on the fine grades. Aside from any tendency to want to press harder to make the abrasive work better papers like 2000 are themselves much more compliant than the rougher stuff. I sharpen big blades on whole sheets of wet and dry on big bits of foam that are a little softer than a mouse pad. It's even easier to see the effect on that. Fine stuff up the 2000 end wants to wrap the edge readily whereas 120 doesn't. Either ease off on the pressure when using the fine stuff or make your backing stiffer. It's probably worth you going to 400, and when you're happy you've got it all dandy there carefully working back to 2000 again and strop.
 
I have experienced the same struggle, but I think I identified the issue. For me, it was that the blade angle was too steep, and I was using too much pressure. For example, if the original bevel is 20 deg, and you use that angle on the pad, I think you end up dulling the edge if you use too much pressure. I think the compression of the pad actually drags the abrasive across the edge, if that makes sense. I had better luck keeping the blade angle a bit more acute, and using less pressure (I have heard the pressure described as what you would use to shave). My grit sequence is usually 320,600, 1000, 1200. Make sure the paper is held flat on the pad (I tape it down with blue painter's tape). Once the edge is convex, it should only take a few light swipes with the finer grits to resharpen. Watch out for the rounded edges on the mouse pad- be sure you start behind those. I am no expert, but that has been my experience. I did notice that I had a harder time with a 6" blade than a 3" blade. I can't explain why. Maybe the pad was too small to get the motion down.
 
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"I did notice that I had a harder time with a 6" blade than a 3" blade. I can't explain why. Maybe the pad was too small to get the motion down."

Makes sense. Although this method is more forgiving than others regarding the angle at which the edge hits the abrasive each time it can be easy to dig either end of a long blade down too deeply, get the wrapping effect, and round the edge. The longer the blade the easier it is to do that. Doing goloks can be a git for that. You can be hitting one bit great whilst rounding of another. Similarly one sees people get knives sharp up at the handle but can't do the belly, or the opposite. Makes me think a short Wharnie has to be the easiest to learn on.
 
i dont think he's stropping his edge. i'm going to call him tomorrow and find out exactly what the problem is and resolve his sharpening problem.
 
C Bryant, if you started with a knife that didn't really need sharpening, then 2000 was plenty coarse enough. With a knife that is already sharp, there is no need for coarser paper. Also, it sounds like you are on the right track with the Sharpie.

As others have more eloquently said above, you are using some combination of:
1. too much pressure ("buttering toast" is a good guide to pressure, I like "shaving my face with a disposable")
2. too steep an angle -- this is an easy way to wrap the abrasive around the trailing edge and blunt it. IMHO, this is worse than too much pressure.
3. too soft a backing. In combination with #1 above (and to a lesser extent #2), this will bury your edge in that sandpaper and round it right off.

Try slathering up the entire bottom half of the blade with the Sharpie, starting with a very flat angle, and gradually working up to a steeper angle until the marker just disappears from the edge. Any steeper is too steep.

PS -- thanks for checking out the vids. :D:thumbup: Hope they helped.
 
The only thing I would add to Tradja is keeping an eye on the blade profile. If you have a very shallow convex - you want to convex more of the edge - if the convex is more of a edge convex - you want to go a little steeper.

TF
 
You guys rock! Thanks for all of that info. KEEP IT COMING!!

*I would have to agree that I was probably using too much pressure.
*I think I was ok with the angle....kind of. I made sure to pay attention that the angle was not too steep, hell I was nearly laying it flat (seemed like it anyway).
*Back to pressure, I bet that the mousepad was too soft for the pressure I was using. If lighten up with the pressure, I think the mousepad would be just right.
*I was using 2000 girt because the blade had a decent edge on it to begin with. I needed a practice subject so I figured 2000 would be good to maybe clean it up a bit.
*As baldtaco-II was saying, I did notice that right at one spot on the belly of the blade I seemed to get the edge really nice, it was actually sharp. I must have had my stroke just right to hit that spot but not the rest of the blade.

That being said.....
Now that I have successfully rounded my edge and made it almost useless...or better stated dangerously dull, what grit should I use to bring it back? Keep in mind I don't need to reprofile the edge, just bring it back.

Richard- I will talk to you tomorrow, looking forward to it.
Tradja- Those videos are fantastic, thank you.

Thanks again to all of you who offered up some info, I really appreciate it,

KEEP IT COMING! I am determined to get this!
 
I have found that the belly of the blade gets sharp faster too - I think it is because from heel to tip - it is always getting the most contact with the abrasive. You have to watch this.

TF
 
Derrick and many other knowledgeable convex dudes do tip-to-heel (there is a very brief chapter on this among the KSF vids at his request).

I have started to sharpen this way, but my tips, belly, and straightaway all get pretty sharp using either tip-to-heel or heel-to-tip.
 
Less pressure and keep the knife at a very shallow angle. When I do it, the spine is only about 1/4" or slightly less off the mouse pad. The tendency, if you are used to sharpening v-bevels is to match what appears to be the bevel angle with angle you are holding it. On a convex you want to hold the knife much shallower then the actual angle (or convex) at the edge. The mouse pad will wrap around and form that hump on its own. If you are lifting the spine to high (making a more obtuse angle) the wave of the mouse pad will wrap over the edge and dull it.
 
BTW...in case you guys didn't pick up on it, tradja is the guy who made the vids on my site.

He is one heck of a teacher. The videos using a 2x4 to explain convex edges is simply brilliant.
 
Disclaimer: I've just dabbled with free-hand convexing of edges and had mediocre results.

I'm a proficient free-hand sharpener using flat, hard stones/hones. With practice its fairly easy to just feel the angle as you draw the blade across the stone. As a beginner I spent more time looking at how far the spine is lifted from the stone.

But with convex sharpening it seems like you are adding another variable, the amount of downward pressure exerted against the sharpening medium. So now you have to make sure the angle is consistent, without being able to feel the shape, and you need to make sure that you are using the same amount of pressure with each stroke. This all just seems so much more complicated and inexact, what am I missing?

Using power equipment to convex an edge makes perfect sense to me, hold the blade right for one or two passes and voila nice and sharp, but for free-hand sharpening, it seems like such a nightmare.
 
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a belt sander is the only way to go. when i started making knives over 17 years ago thats how i done it. almost every knife i made was a convex edge blade.
 
Ok, here is another question for ya....

I'm sure this is somewhat dependent on the manufacturer of the paper, but how long can I expect a piece of this very fine grit sandpaper to last? It seemed like it lost it's abrasive quite quickly. Is it good for a few sharpenings or should it last a while? Being so fine it is difficult to tell if most of the abrasive was gone or if it was just a bit worn down.

Hey Richard J, give me a call sometime this week after 1pm my time if you can. I should be available to chat.
 
I actually did it kind of on accident just a few days ago...Once I figure out what I did I will try and post...
 
ok guys, I used a bunch of the tips you gave me and had a bit more luck. The blade is shaving sharp, but about half of the edge is like that. From right where the belly starts back from the tip to the middle, maybe 3/4 of the way to the handle is pretty sharp, the rest is fairly dull. So a bit more practice and I might be somewhat competent at it! This time I use a piece of leather instead of a mousepad (I still think the mousepad has potential) and pretty much pretended I was buttering toast. Worked decently. Thanks for the tips so far, and if any of you guys think of anything else plese feel free to add it here!
 
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