Convex blade sharpening

[C_Claycomb]

Falling Rain,
Re the WD-40, I would use water instead. I find that WD40 evaporates too quickly and you end up with a gummy paste of steel and abrasive particles on the paper. Water washes the particles away much better.

Due to the way that the Hoodoo hone removes metal, I believe it is necessary to reduce the angle that the blade is held. If the knife is held at the normal angle that one would use on a bench stone it doesn't work so well. The rubber mat gives under the pressure from the blade such that the very cutting edge meets the abrasive at a greater angle than one really wants. It is possible to sharpen a convex edge on a flat stone, just so long as it is just a touch up, and not a regular thing. Just kiss the very edge of it with the stone, you can do more, but that takes (a little) more practice than using the wet-n-dry method.

Think of it this way, a convex edge is just a series of flat facets with the corners knocked off

As for wanting to get it sharper before stropping. Do you use the same Hoodoo hone to sharpen your scandis, or are those done on a water stone? I find that due to the way the abrasive on the Hoodoo hone removes metal, you get more of a burr than you would on a water stone, and unlike on a water stone, you can't easily change the angle for the last couple of strokes to remove that burr. For convex edges, stropping is part of the sharpening process, it is much more important than it is for flat ground edges.

If you really want to know how to sharpen convex edges, have a look at Longstrider's collection of Fallknivens

Whatever you do, don't go and flat grind a perfectly good convex bevel, at least, not if you are doing so just because you haven't worked out how to sharpen it

 

[Andy]

when practicing sharpening I always advise using a really fine abrasive dry with some felt tip to get a feel of where your removing metal from. The reason for the fine abrasive is that it won't remove as much metal when your doing it wrong so wont be such a big problem to correct later, if you use wet paper the felt tip will get washed off

I aim to remove metal from the edge to a bit past the lamination marks on my F1, if your using the soft side of a mouse pad the angle will be really low. Don't put much pressure on as you will round the edge. I go upto about 1200 on the soft side and then flip the mouse pad over and polish the edge with 2k /2.5k grit. At home I'll then give it one or two very light strokes on a hard stone (sharpmaker in my case) to make sure there isn't a burr left (stropping any knife when there is a burr you can feel will leave a weak edge, by using fine ceramics you cut off the weak metal.

 

[falling rain]

Falling Rain,
Re the WD-40, I would use water instead. I find that WD40 evaporates too quickly and you end up with a gummy paste of steel and abrasive particles on the paper. Water washes the particles away much better.

Due to the way that the Hoodoo hone removes metal, I believe it is necessary to reduce the angle that the blade is held. If the knife is held at the normal angle that one would use on a bench stone it doesn't work so well. The rubber mat gives under the pressure from the blade such that the very cutting edge meets the abrasive at a greater angle than one really wants. It is possible to sharpen a convex edge on a flat stone, just so long as it is just a touch up, and not a regular thing. Just kiss the very edge of it with the stone, you can do more, but that takes (a little) more practice than using the wet-n-dry method.

Think of it this way, a convex edge is just a series of flat facets with the corners knocked off

As for wanting to get it sharper before stropping. Do you use the same Hoodoo hone to sharpen your scandis, or are those done on a water stone? I find that due to the way the abrasive on the Hoodoo hone removes metal, you get more of a burr than you would on a water stone, and unlike on a water stone, you can't easily change the angle for the last couple of strokes to remove that burr. For convex edges, stropping is part of the sharpening process, it is much more important than it is for flat ground edges.

If you really want to know how to sharpen convex edges, have a look at Longstrider's collection of Fallknivens

Whatever you do, don't go and flat grind a perfectly good convex bevel, at least, not if you are doing so just because you haven't worked out how to sharpen it

Well I spent 2 hours sharpening my Nl5 Idun the other night and am more confused than ever now. I tried sharpening again drawing the knife away (as with stropping) with not much luck. I then tried drawing the knife across the hone very carefully with the edge leading using alternate strokes on each side of the blade and got the edge pretty sharp and keeping the convex shape. (this seems to go against the advice on using the Hoodoo hone). I then tried stropping very carefully as normal and ended up blunting the edge off again I use my waterstones for scandi grinds and strop with no problems at all. I hook the strop to a door handle for this. Do I need to lay the strop flat on a hard surface for stropping a convex blade I used a small angle to sharpen drawing the blade with the cutting edge trailing but not much luck starting with a course grit moving onto a finer grit. When I did the same with the edge leading (as with a scandi grind sharpening) it seemed to work better As for using water instead of WD40 I would have thought the slurry you get with the WD40 would have helped with the sharpening. I'll give it a go again with water then Chris. Try everything. I can get my Sami, frost's mora, and other scandi super sharp but am struggling getting the convex blade as sharp as them. I certainly don't want to re-profile the convex blade ....................I just want it sharp

 

[addyb]

I don't mean to sound rude, but maybe you're overcomplicating things? Here, try this.

It's a page that I found on google one night a long time ago and I think it gives very plain, straightforward instructions. For a strop I just take my leather belt off of my blue jeans and hang it from my closet door. I paste some buffing compound onto it and pull it as taught as I can get it. (A loose strop will dull your blade instead of helping it) Every single knife I use this method on reaches the "scary sharp" stage within minutes. Even little Swiss Army Knives. If I'm really in a sharpening mood then I'll cut a chunk out of an old cereal box, lay it flat on my desk, paste some buffing compound onto it and strop with it. But that's only for blades that are flat ground.

Good luck!

Adam

 

[Hoodoo]

One of the problems with the mousepad technique is that if you press too hard and/or hold at too steep of an angle, you can roll the edge. You can try to use a stiffer piece of rubber or even a piece of thick leather as backing or just don't press so hard or hold the knife as steep and take your time.

 

[addyb]

Touche' sir!

 

[C_Claycomb]

As a final resort, you could ask around and find someone trustworthy on here who is used to sharpening convex edges and let them have a go. I am not saying this as a solution, but if they are able to put the kind of edge on the knife that you want, then at least you will know that it is possible, and just a matter of technique. At the moment it sounds as if you are beginning to doubt that it can be done

I too often sharpen on a hard stone, initially having the blade go in both directions on the stone, towards and away from the edge. I role the angle of the knife to work the convex, then finish off the last few strokes into the edge at an angle that touches the edge and little more, then strop.

As has been said, pressing down too hard while stropping will blunt the edge.

I don't know whether you are factoring in blade angle to the comparison with your scandi knives, if is possible that they all have smaller included blade edge angles than the Fallkniven. that alone is going to make them seem sharper.

 

[Longstrider]

As a final resort, you could ask around and find someone trustworthy on here who is used to sharpening convex edges and let them have a go.
--- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- --- ---
If you really want to know how to sharpen convex edges, have a look at Longstrider's collection of Fallknivens

I can take a hint Chris (and appreciate a compliment when I see one)

Falling Rain, if you want me to take a look at your knife, I'll do so willingly for the price of the return postage. Thickness of blade should be no barrier to edge sharpness. My A2 has a 6mm thick blade but will shave my arm no problem.

One thing that I have noticed with the way many people use the mouse mat and W+D technique with convexed blades is that they worry about scratching the blade so hold the knife at too much of an angle to the W+D. This leads to the edge still being convexed but at a far steeper angle than it should be. The actual edge may end up as sharp, but the blade thickens so quickly behind the edge that it seems hard to use. It's a bit like the difference between a sleek looking speedboat and a narrowboat. The sharp bit is just as thin, but the body becomes too thick too quickly to make using the blade effectively a nightmare. The trick with this method is to sharpen with the blade virtually flat on the mouse mat, allowing the contour of the depression it makes in the mat determine the shape of the grind, use finer and finer paper until the whole blade is ready for stropping, then strop the whole width of the blade. This way you get no scratches and a very acceptable edge.

As a few of the guys here know, I sharpen pretty well everything with my DMT Diafolds followed by a loaded strop. These are flat diamond hones but they are still a very effective tool for convexed edges if used correctly. I use this method on all my fully convexed knives and my axes (all convexed) and can shave arm hair with any one of them all day long (well, at least until I run out of arm hair! *LOL*)

 

[sharp88]

Laying the blade flat on the stone and gradually tilting the bevel until you reach the end of the stone and the required edge angle worked for me fine. I did this with my F1 a couple of hours back n gave it a good strop n it was popping hairs off my arm and slicing paper without taring it great.

 

[Simon E]

I find that if you steel the knife (or use a ceramic steel) after the mouse pad trick, the hairs will fly off, I mean its insane and you will look like Chewbacca with mange but they really do fly off

Get a #1200+ ceramic steel and see what I mean.

*If you are not familiar with the technique its nothing like you see a chef do. Place the steel in an upright (90 deg) position and place the blade at an angle that seems way too obtuse. Then allow the blade to travel down the steel using only the weight of the knife, do not press, it will seem like you are not doing anything, but you can go from seemingly blunt to scalpel very quickly. So the blade goes against the steel, let it drop/rub against the steel and draw it back to that it goes from handle to tip nice and slow. Two or three times each side should have it hair popping sharp.

 

[OldJimbo]

The most valuable tools I have for sharpening are a lens and a felt pen. My bet is that either the edge is not uniform and so you are only sharpening parts of it, or that there's some steepening of the convex at the edge so that prevents proper sharpening. If my bets are wrong and the problem is some sort of edge rolling of a wire edge, then the lens will pick that up too.

 

[Hoodoo]

As an aside, I don't know what most folks do when they use sandpaper but this works well for me. When the paper gets loaded up, I use a toothbrush to clean it. I don't use water or anything else, just a toothbrush to remove the debris.

 

[addyb]

Hoodoo,

That's a spectacular idea and I would never have thought of that. When my paper's loaded I usually just go and buy more. See, this is why you're in the management (mod) and I'm not!

Adam

 

[Hoodoo]

Hoodoo,

That's a spectacular idea and I would never have thought of that. When my paper's loaded I usually just go and buy more. See, this is why you're in the management (mod) and I'm not!

Adam

That's why Tony pays me the big salary. Don't tell the other mods though.

 

[falling rain]

I can take a hint Chris (and appreciate a compliment when I see one)

Falling Rain, if you want me to take a look at your knife, I'll do so willingly for the price of the return postage. Thickness of blade should be no barrier to edge sharpness. My A2 has a 6mm thick blade but will shave my arm no problem.

One thing that I have noticed with the way many people use the mouse mat and W+D technique with convexed blades is that they worry about scratching the blade so hold the knife at too much of an angle to the W+D. This leads to the edge still being convexed but at a far steeper angle than it should be. The actual edge may end up as sharp, but the blade thickens so quickly behind the edge that it seems hard to use. It's a bit like the difference between a sleek looking speedboat and a narrowboat. The sharp bit is just as thin, but the body becomes too thick too quickly to make using the blade effectively a nightmare. The trick with this method is to sharpen with the blade virtually flat on the mouse mat, allowing the contour of the depression it makes in the mat determine the shape of the grind, use finer and finer paper until the whole blade is ready for stropping, then strop the whole width of the blade. This way you get no scratches and a very acceptable edge.

As a few of the guys here know, I sharpen pretty well everything with my DMT Diafolds followed by a loaded strop. These are flat diamond hones but they are still a very effective tool for convexed edges if used correctly. I use this method on all my fully convexed knives and my axes (all convexed) and can shave arm hair with any one of them all day long (well, at least until I run out of arm hair! *LOL*)

Thanks for the offer longstrider. Buckshot has said he'll go over it with me and he lives nearby in Oxford so if all else fails I'll take you up on your kind offer. :You_Rock_ I guess I'm just simply not used to convex blades. I sharpen my GB Small forest with the GB axe stone puck and can get that beautifully sharp. As i do with my other flat grinds. It seems that despite all the great advice from folks it's one of those things that I need to be shown in person than try to follow written instructions. --- Well it is for me anyway not being the brightest pixie in the forest Thanks for everyones advice. It's going to be another 'bow drill' for me this one. Chuffed to bits when I finally get the hang of it finally

 

[OldJimbo]

Yep, Hoodoo has good ideas: it was his advice which started me using a lens all the time.

 

[Hoodoo]

Yep, Hoodoo has good ideas: it was his advice which started me using a lens all the time.

Well Jimbo, I think both of us are like the proverbial blind squirrel that finds a nut once in awhile.

 

[falcon]

I was chatted to a guy selling knives at the WG about my previous difficulties sharpening the F1and he offered to sort it out. Basically he gave it a fairly brief going over with ceramic stones inclining the blade at a fairly steep angle due to the convex grind. Result...an instant and significant improvement..

 

[Longstrider]

Falcon, The thing to watch out for with the method you describe is that some folks will sharpen the thing by only touching the edge with the hone. This is fine for the occasional light touch up, but over time will lead to the edge becoming too thick to be servicable as the edge is worn away and becomes thicker and thicker with a very obtuse edge angle.. To correctly sharpen a convex blade you should remove steel from the whole of the grind, not just the very edge.
Ceramics tend to be pretty fine so doing this occasionally should be no problem, just don't think it will be one and only answer to long-term edge retention on a convexed knife.

 

[falcon]

......so it's important to use the Hoodoo hone to remove metal from a deeper portion of the convex grind then?....cheers