This is a new thread born out of another on steel quality and progress. Part of the discussion turned to the use of lower edge angle than normal, less than 10 degrees per side. It was posed that some sharpening research and references recommend minimum angles of 15 dps (degrees per side). Rather than muck up an already long thread, I thought starting a new one would be better. The sharpening references used so far are Leonard Lee's The Complete Guide to Sharpening and Dr. Verhoeven's paper on experiments in knife sharpening. Lee's book is a great resource and covers sharpening everything from adze's to nail clippers. Verhoeven's work looks at the best way to finish a shaped edge and remove the edge burr.
I'm not sure where the fixation on 15 dps comes from, as Lee doesn't follow that recommendation. To expand beyond knives, he uses paring chisels for wood work with angles of 15 degrees inclusive. For camp and utility knives, he recommends 12 to 15 dps edge angles, finely polished. For kitchen knives, he recommends the unusually low angle (even for me) of as little as 5 dps, finished with a little tooth, say 1000 to 1200 grit in waterstones, or medium grit, such as a Norton Fine India stone.
I've read Verhoeven's sharpening paper and don't remember it being recommended there either. He found in one experiment that going from 20 dps to 10 dps caused excessive edge roughness when ground on the Tormek 220 grit coarse stone, but an intermediate step on the Tormek waterstone essentially alleviated the issue. It is not clear whether the issue was caused by the low angle only, or a combination of low angle, coarse grit, or issues inherent in powered wheel sharpening. Likely it is a combination of all of these. Coarse grit is accentuated at lower angles, and sharpening on a powered wheel at low angles was very sensitive to wheel eccentricity, even with freshly dressed wheels.
It's also worth noting that one of the standards for edge quality was a hand honed straight razor with an edge angle of ~8.5 dps. So, is honing at a lower angle more difficult? It would seem so with powered sharpening wheels. His experiments did not cover the level of difficulty with hand honing at such low angles.
Personally, my edge angles have been creeping down over the last few years. I now run EDC knives in the 7-12 dps range, with a microbevel 2-3 degrees higher to ensure efficient use of very fine finishing abrasives and to help ensure the removal of any small burr remnants from coarser shaping. This has proven durable for even work tasks, such as cutting fire proofing from beams, caulk from concrete, and even light metals for the 7 dps edge.
My most used chopping knife is running around 15-17 dps, with a small microbevel for the same reasons. This has proven durable during yard work, including root cutting and cutting of invasive TV antenna wires. I actually think I could go lower, but haven't had the motivation to lower the bevel angle down to 12.
The down side to running these lower than normal angles is the time it takes to rebevel the knives. As long as the bevels are sharpened with out dry power tools, even digging, accidental rock impacts, and occasional twisting against concrete has not caused excessive damage (deeper than the edge bevel width), and in all cases so far, the damage has been removed in 3 sharpenings or less, except for the rock impacts on the chopper. The steels so far are 1055, H1 (Spyderco), and an AUS-6 class steel, though the exact grade isn't known. I will say, using lower angles like this, one starts to appreciate Spyderco's and slip joints more. There are no thumb studs to get in the way.
I'm not sure where the fixation on 15 dps comes from, as Lee doesn't follow that recommendation. To expand beyond knives, he uses paring chisels for wood work with angles of 15 degrees inclusive. For camp and utility knives, he recommends 12 to 15 dps edge angles, finely polished. For kitchen knives, he recommends the unusually low angle (even for me) of as little as 5 dps, finished with a little tooth, say 1000 to 1200 grit in waterstones, or medium grit, such as a Norton Fine India stone.
I've read Verhoeven's sharpening paper and don't remember it being recommended there either. He found in one experiment that going from 20 dps to 10 dps caused excessive edge roughness when ground on the Tormek 220 grit coarse stone, but an intermediate step on the Tormek waterstone essentially alleviated the issue. It is not clear whether the issue was caused by the low angle only, or a combination of low angle, coarse grit, or issues inherent in powered wheel sharpening. Likely it is a combination of all of these. Coarse grit is accentuated at lower angles, and sharpening on a powered wheel at low angles was very sensitive to wheel eccentricity, even with freshly dressed wheels.
It's also worth noting that one of the standards for edge quality was a hand honed straight razor with an edge angle of ~8.5 dps. So, is honing at a lower angle more difficult? It would seem so with powered sharpening wheels. His experiments did not cover the level of difficulty with hand honing at such low angles.
Personally, my edge angles have been creeping down over the last few years. I now run EDC knives in the 7-12 dps range, with a microbevel 2-3 degrees higher to ensure efficient use of very fine finishing abrasives and to help ensure the removal of any small burr remnants from coarser shaping. This has proven durable for even work tasks, such as cutting fire proofing from beams, caulk from concrete, and even light metals for the 7 dps edge.
My most used chopping knife is running around 15-17 dps, with a small microbevel for the same reasons. This has proven durable during yard work, including root cutting and cutting of invasive TV antenna wires. I actually think I could go lower, but haven't had the motivation to lower the bevel angle down to 12.
The down side to running these lower than normal angles is the time it takes to rebevel the knives. As long as the bevels are sharpened with out dry power tools, even digging, accidental rock impacts, and occasional twisting against concrete has not caused excessive damage (deeper than the edge bevel width), and in all cases so far, the damage has been removed in 3 sharpenings or less, except for the rock impacts on the chopper. The steels so far are 1055, H1 (Spyderco), and an AUS-6 class steel, though the exact grade isn't known. I will say, using lower angles like this, one starts to appreciate Spyderco's and slip joints more. There are no thumb studs to get in the way.
