Hard Surface Convex Sharpening?

M

Mtn Hawk

Joined
Nov 8, 2005
Messages
270
There are a lot of instructions, tutorials, threads, posts, etc., about convex sharpening on a soft surface (such as sandpaper on a mousepad) but I haven't seen much about sharpening on a hard surface. Using a hone for both relief grinding and convex sharpening saves weight in the wilderness. I'm aware that freehand relief grinding puts on a slightly convex edge but on some knives I like a little more metal behind the edge.

I know that convex sharpening on a hone must be done with an edge-trailing stroke and the spine must gradually be raised as the stroke progresses. I'm getting fairly decent edges this way but there is room for improvement. If someone can be more specific and detailed I'd appreciate it!
 
i like to do a relief grind with a course grit paper at a very low angle.

but i used to do convex on a stone before i got some sandpaper...

just basically do what you described, and take each stroke at a slightly different different angle. rolling each stroke works too. make sure you are hitting the whole edge edge though, don't miss any spots.
 
Convex Sharpening on a Hard Surface Stone:

Sharpen edge forward, spine trailing. I start with the highest angle I want (at the very edge), and as I push the blade forward, I smoothly drop the angle down just a bit. You don't need very much difference in angle to accomplish a convex edge.

Work your way down the length of the blade.

Hone or strop edge trailing as usual.
 
The best way I have found to sharpen a convex edge in the field is to put a sheet of sandpaper of your leg.
 
siguy said:
take each stroke at a slightly different different angle.
Click to expand...

This is the only way I put a freehand convex edge on. Does't seem to be mentioned often in convex sharpening threads, though. A lot less chance of rolling the edge than with a soft surface. Start in the middle, then do the lower strokes, then the high strokes. With an aggressive strop (large abrasives) you can make it look real pretty in no time. Varying the angle during the stroke is much harder to keep consistent for me.
 
Thanks for the replies!

siguy-- I also relief grind at a very low angle. This makes a big difference in cutting and chopping efficiency. I've used sandpaper but hones are easier for me.

take each stroke at a slightly different different angle
I never thought of this. As Broos said, it isn't mentioned much. Thanks for bringing it to my attention! :)

Grampa-- I've never heard of the edge-forward method but will give it a try. Would this decrease the chance of rounding the edge?

3wolves-- Good idea, but to keep my pack weight down a hone does double-duty for both relief grinding and sharpening.

Broos-- Thanks for the additional info!

Would you please give me some suggestions for large abrasives? I'm currently using chromium oxide (0.5 micron) but I think this is too small.
 
diamond paste or spray is available to pretty large sizes. I have some 10 micron and it is WAY more aggressive than CrO2. Even 1 micron diamond paste seems much more aggressive than plain CrO2 to me. I've been meaning to try some 20 micron diamonds, also. I think Bark River has some larger abrasives you could use, too (I haven't tried it yet but reviews are good).
 
Last edited:
When I put a convex edge on a blade using benchstones, I just sharpen in sections and my shoulders, elbows, and wrists make sure it's convex whether I wanted it to be or not. I use edge-leading and edge-trailing until I'm ready to remove the burr. Then, I either do all edge-trailing or start each side edge trailing and move on to edge leading to finish (depending on whim). Has worked so far.
 
IIRC, none other than Bill Moran -- who's sort of considered the Father of the Convex Grind -- maintained his with a regular benchstone. And another not-so-obscure guy, Jerry Fisk, does the same. Again IIRC, Fisk has said that all he does is make every 4th or 5th pass on the stone at a slightly greater angle, freehand of course, which easily produces a convex edge. So in a way it's one of those skills that's almost so easy, it can elude us. :)
 
Maybe I'm missing something, but if each sharpening stroke is done at a slightly different angle, as siguy suggests, then wouldn't a convex edge be obtained by drawing the entire edge across the stone on each stroke? If so, it seems this would be easier and quicker than convex sharpening in sections, as is done on a soft surface.

Broos-- I appreciate the info. That gives me a good abrasive range to play around with.

thombrogan--

I just sharpen in sections and my shoulders, elbows, and wrists make sure it's convex whether I wanted it to be or not
So, basically, you are sharpening as if you are forming a microbevel, only doing it in sections rather than drawing the entire edge across the stone? I know that it's impossible to consistently hold the same angle freehand, so some convexity will naturally occur.

I use edge-leading and edge-trailing until I'm ready to remove the burr.
I raise a burr on both sides when relief grinding and take it off with a few slightly higher-angle edge-leading strokes. After that, I sharpen at a slightly higher angle than the relief grind, alternating sides with each stroke (to keep both sides of the edge equal), so no burr forms. Should I not alternate sides during this stage so a burr is formed?

Dog of War-- Great info!

So in a way it's one of those skills that's almost so easy, it can elude us.
Yes, good point and I understand that well. :) Many times I've missed a simple and obvious solution by looking for the complex.


Thanks again to everyone for the replies! This info is very helpful and interesting.
 
Thanks for the history, DOW!

Ask Thom about cubic boron (?) - it may even be better than diamonds.
 
mtn hawk, i personally use the stropping motion in long sweeps along the entire edge for each pass, instead of doing sections at a time. so just like when i sharpen on a stone, but edge trailing.

also, a note that i had forgot; whenever i sharpen on a stone with edge trailing, i tend to convex the edge by accident. when edge leading, i have a much crisper edge. that might be something to think about and experiment with...
 
Mtn Hawk said:
So, basically, you are sharpening as if you are forming a microbevel, only doing it in sections rather than drawing the entire edge across the stone? I know that it's impossible to consistently hold the same angle freehand, so some convexity will naturally occur.
Click to expand...

It's just the natural convexity that occurs from being human.

Mtn Hawk said:
Should I not alternate sides during this stage so a burr is formed?
Click to expand...

You should keep doing what you're doing. There's no preventing burrs, so everything that discourages or eliminates them is good. Forming a large burr when only a microscopic almost theoretical burr is possible just creates more work, wastes more steel, and eats up into the relief grind you worked so hard to create.

Broos,

I know nothing about boron carbide powder. Other than Keith DeGrau sells 1 micron paste that's handier than the 0.7 micron powder I got from ESK Ceradyne and you don't have to order in huge quantities from some Bundes Republik called Deutschland.
 
If you sharpen with a stone free hand, you will create a convex edge.

It's just the natural variability in the human machine.

You don't have to work to do it, it will just naturally occur.
 
I sharpen with a 3 inch black hard arkansas stone held in the hand. Edge trailing strokes with a slight rolling motion, as if I were stropping. Always turn out perfect, polished, hair whittling convex edges this way. Been freehanding the same way for years and years now.
I think DoW has the right idea there, it's just one of those things that's so natural and simple that you should almost be doing it absent mindedly to do it right. Otherwise you're bound to overthink it and wind up with only a So-So edge. My two cents for what they're worth.


Gautier
 
siguy--

...whenever i sharpen on a stone with edge trailing, i tend to convex the edge by accident. when edge leading, i have a much crisper edge. that might be something to think about and experiment with.

I sharpened a Mora today, edge leading and slightly varying the angles, as you suggested, and got a significantly better edge! The hair I shaved seemed to pop off more than scrape off, which is the level of sharpness I am looking for. Sharpening just one knife isn't enough to draw a definite conclusion but I'm happy about it and will definitely continue to experiment with this method.

I appreciate you and others pointing out that freehand edge leading strokes will give convex edges. I was stuck on the idea convex edges could only be done with edge trailing strokes because that's the way it's done on a soft surface. It's kind of ironic that I used to obsess about consistently maintaining the same microbevel angle. Now I find out that it's better if I don't!

thombrogan-- Good points about burrs!

Grampa-- Yes, I see what you mean. I've had poor results convex sharpening on a soft surface but have heard so many good things about convex edges from you and others that I didn't want to give up on them..

Gautier-- I'm not getting quite the edges I want this way but it could easily be "operator error" or "overthinking" (wouldn't be the first time). I like to experiment with different techniques and haven't given up trying.

Everyone's suggestions and information have been very helpful and much appreciated!

PB Wilson-- That's a question someone more knowledgeable than I am will have to answer.
 
I always finish my convex sharpening on hones edge leading. As for dished hones I like them as flat as possible with them dished for me it is harder to keep a low final angle of a convexed edge.
 
i never considered flat stones to be important.. till I started accumulating good stones and knives in quantity..

flat matters. dished is doable, especially if you're a one rock kinda guy who knows his rock.. but flat REALLY HELPS on bigger blades, whereas it's not as critical with smaller ones.

80% of my work is edge-leading, i do about 10% of it with knife held firm, STONE MOVES (very small burnishing stones) .. and 10% edge trailing (on my finest japanese stones that're worth several times more than the knife).. but the edge trailing is to protect the ROCK, not the blade..

i sharpen edge first and do NOT sharpen the EDGE FIRST.. working behind the edge (what everybody tells you to check you're not doing) .. to start with, then gradually working down TO the edge.. i dunno how you could possibly do it the way i do and NOT get a convex edge.. just repeatedly 'grind down the shoulder'.. whereever it decides to be.. and repeat on the next finer grit...

when you've got about 5/16 of an inch of mirror along the edge from heel to tip.. work on the tip a little more very gently. RIGHT AT the tip.. VERY gently.. points are hard to do correctly, it takes a clear eye and patience. Due to the taper of some points from all 4 directions you sort of estimate the arc angle and extend it but the last 1/4 inch of the tip is hardest to accomplish. GENTLY is the way, don't take too much, polish your way there .. fast can wait..

if you think you're too SLOW but you get good results, shaddup.

if you're fast but it's not perfect, slow down.
 
You must log in or register to reply here.
Back
Top