OK, what is the proper angle and motion for sharpening convex edges with sandpaper? I'm wanting detailed advice on everything from how you hold the knife to how you move your hands while doing it.
Up until now I've been using Japanese waterstones and have gotten proficient at sharpening my gyutos with a 90/10 edge and got the Murray Carter DVD, sharpening with a very low angle, works great for double bevel and single bevel edges. I also removed the bevel shoulder/convexed a couple of knives on the waterstones by varying the angle, it worked but seemed like using strops might be easier and faster.
I finally set up some leather strops and sandpapers as recommended by Mike Stewart and tried them on several convex knives: a Dan Koster santoku and a "table knife" from Valiant, both full convex ground, as well as a Tosagata white steel Satsuma knife which I had previously convexed myself. The Tosagata seemed to sharpen up just fine, but because the edge is rather thick it's not quite as sharp as a thinner blade would be. The Koster knife came with a flat bevel from the grinder, I had to remove the shoulder with sandpaper, it also got very sharp but not as sharp as a thinner blade would be. The spine is between 3/32 to 1/8" thick, full convex grind. It cuts pretty well now. On these two knives I only stropped near the edge, I did not do the blade surface.
The table knife came as a small "gift" from Valiant after I had to return one of their goloks for repair. It looks like a butter knife, but the convex edge was sharp as hell when I got it. It is thin and fully convex. I've read everything I could find on convex edges, they say that to properly sharpen a convex blade, a little metal should be removed from the entire surface of the blade each time it is sharpened. OK, so I laid the blade flat on the papers with the leather strop on wood underneath, after going through grits from 400 to 1500 and then with black buffing compound, I found the blade got a lot duller than it had been previously. So trying to remove metal from the entire side didn't make it sharp.
I had also read somewhere else to tip the blade up until it bites into the leather, in order to find the correct angle where you'll hit the edge. I tried this, but the angle seemed so high that I did not even attempt to strop at such a high angle, I was sure it would dull the blade further.
In the end the only technique which seemed to restore some sharpness to the blade was to strop at about a 15 degree angle like one would use on a stone. Only the lower portion of the blade contacted the abrasive with this method. It's so-so sharp now, but I don't think it's as good as the original edge it had.
It is said that to prevent the edge from gradually thickening over repeated sharpenings, metal should be removed from the entire surface each time. It seems like one would have to vary the angle in order to hit all parts of the blade: Do the upper part near the spine first, then strop the edge last to restore any sharpness lost in the previous step.
Questions: 1) What angle should be used? 2) Maintain a constant angle while stropping, or is any wrist motion used during the stroke?
Using strop/sandpaper didn't seem as easy as people say, I was able to sharpen the blades, but my results are not as good as what I'm getting with stones. So I conclude that my technique must be lacking!
Up until now I've been using Japanese waterstones and have gotten proficient at sharpening my gyutos with a 90/10 edge and got the Murray Carter DVD, sharpening with a very low angle, works great for double bevel and single bevel edges. I also removed the bevel shoulder/convexed a couple of knives on the waterstones by varying the angle, it worked but seemed like using strops might be easier and faster.
I finally set up some leather strops and sandpapers as recommended by Mike Stewart and tried them on several convex knives: a Dan Koster santoku and a "table knife" from Valiant, both full convex ground, as well as a Tosagata white steel Satsuma knife which I had previously convexed myself. The Tosagata seemed to sharpen up just fine, but because the edge is rather thick it's not quite as sharp as a thinner blade would be. The Koster knife came with a flat bevel from the grinder, I had to remove the shoulder with sandpaper, it also got very sharp but not as sharp as a thinner blade would be. The spine is between 3/32 to 1/8" thick, full convex grind. It cuts pretty well now. On these two knives I only stropped near the edge, I did not do the blade surface.
The table knife came as a small "gift" from Valiant after I had to return one of their goloks for repair. It looks like a butter knife, but the convex edge was sharp as hell when I got it. It is thin and fully convex. I've read everything I could find on convex edges, they say that to properly sharpen a convex blade, a little metal should be removed from the entire surface of the blade each time it is sharpened. OK, so I laid the blade flat on the papers with the leather strop on wood underneath, after going through grits from 400 to 1500 and then with black buffing compound, I found the blade got a lot duller than it had been previously. So trying to remove metal from the entire side didn't make it sharp.
I had also read somewhere else to tip the blade up until it bites into the leather, in order to find the correct angle where you'll hit the edge. I tried this, but the angle seemed so high that I did not even attempt to strop at such a high angle, I was sure it would dull the blade further.
In the end the only technique which seemed to restore some sharpness to the blade was to strop at about a 15 degree angle like one would use on a stone. Only the lower portion of the blade contacted the abrasive with this method. It's so-so sharp now, but I don't think it's as good as the original edge it had.
It is said that to prevent the edge from gradually thickening over repeated sharpenings, metal should be removed from the entire surface each time. It seems like one would have to vary the angle in order to hit all parts of the blade: Do the upper part near the spine first, then strop the edge last to restore any sharpness lost in the previous step.
Questions: 1) What angle should be used? 2) Maintain a constant angle while stropping, or is any wrist motion used during the stroke?
Using strop/sandpaper didn't seem as easy as people say, I was able to sharpen the blades, but my results are not as good as what I'm getting with stones. So I conclude that my technique must be lacking!
