Alright, massive first post with lots of questions/thoughts but bare with me. I sharpen mainly chef knives/slicers/paring knives and have consistently had issues maintaining a "shaving sharp" edge for any great deal of time (predominantly with larger knives). I have both carbon steel knives and various stainless in a range of rockwell hardness from both Japanese and Western makers alike (mora, victorinox, aus 8, aus10, ginsanko, and sg2 among others). Whilst they maintain working sharpness they become noticably duller after fine slicing only a few bunches of shallots or similar (will still cut but sharpness has degraded by a fair amount). I've spent months trying to figure out the root cause of this. Here are some details about how a general sharpening session would be (I'll include the initial sharpening of a new knife or a knife with unknown edge geometry)
Lets say im about to sharpen a 61 rockwell ginsanko chef knife that is 50mm wide at the heel and 250mm long (similar approach and results with my carbon gyutos as well). I'm free handing and raise the spine of the knife about 5mm off the stone at the heel to set a bevel (this would be around 6 degrees per side?) And typically finish at like 12mm off the stone for the micro bevel (this would be around 13 degrees per side?). My terminology may be incorrect here but those are the angles im using anyway. I typically use back and forth or scrubbing strokes in initial shaping of the edge and move to heel to tip strokes in subsequent sharpenings and when I'm close to finishing a knife
(New knife)
- destress lightly on a flat soaked cerax 700 (or 320 in the case of severely dull knives)
-grind right side until edge stops reflecting light
-lightly destress twice on the same stone again
-grind the left side until the edge stops reflecting light
I pay attention here to whether one side has stopped reflecting light sooner than the other and by roughly how much quicker this process has occurred. As Japanese knives are generally assymetrically ground and sharpened often the right side will be finished much sooner than the left. It's at this point I'm unsure whether to:
-raise the angle on the side that took longer to prepare to account for the assymetry of the blade (and potentially lower the angle on the side that was prepared sooner) to keep the grinding times relatively similar per side
Or
-keep at the same 50/50 angle and grind more on the side that took less time to prepare so that the edge eventually moves closer to the side that originally took longer to prepare, eventually resulting in similar grinding times per side. (This process tends to involve a constant destress and prepare cycle keeping the number of passes per side needed to prepare each side in mind). This can take a while to even out in some cases
Whichever route I've opted for I now know for future sharpenings what angles are required for even grinding on each side. After that initial bevel setting or if I'm touching up that knife after use in the future the process is then:
-destress once lightly on the stone
-grind each side of the blade evenly until the light stops reflecting (This tends to happen rather quickly with decent 300-700 grit stones).
-I will typically make a bit of a slurry on the stone with a diamond plate or nagura and move to alternating heel to tip strokes trying to change the scratch pattern each time. These are made edge leading to reduce the chances of forming a burr (the slurry/mud helps with this). This may typically be about 8 or so per side. Blade slices well at this point and in the case of finer grit stones it may shave also at this point
(Although not important)
-clean off the stone or grab a finer polishing stone
-raise the angle to 13 degrees per side (or in the case of the assymetrically sharpened blade ~8 degrees one side and ~16 the other) and use alternating edge trailing strokes crossing the patterns again to reduce the likelihood of another burr forming. This is typically only around 2 each of heel to tip and tip to heel strokes on each side (In the case I decide to go with an 8k finishing stone I will usually use double these angles however typically I will use a 3000 grit stone). The blade will usually shave ok at this point
-use the same edge trailing strokes at my original shaping angle to "backbevel" and reduce the effect of any 'blunting' the micro bevel bas causes. This can be anywhere from a couple of strokes to like 15 per side. Blade usually shaves even better than previously (although i dont think I've ever been able to get tree topping sharp that people describe. Even my gold dollar straight razor that I use for shaving doesn't do that although I find it fine enough to do the job without any irritability)
At this point I'm pretty confident ive produced a wire edge here despite the apparent keenness. To elimimate it ive been playing around with:
- trying another light edge leading microbevel pass or parallel to the edge. I have also tried doing this with the original shaping angle. As the majority of my sharpening stones are friable waterstones its pretty easy to trash the edge with an edge leading pass without improving it. Using higher grit and harder stones help slightly.
-alternating an edge leading pass at shaping angle on each side on my norton fine followed by alternating trailing passes on a finishing stone (3 or 8k)
I have tried other stones and approaches but overall the blade has felt pretty similar in use at this point.
-There is no light reflecting on the edge, the knife feels to cleanly cut paper and can usually perform a 90 degree push cut on paper pretty easily.
-In the case of the assymetrically sharpened/honed blade it will typically shave at a lower angle on the side with the lower angle applied (generally the right side) compared to the other.
-The 50/50 blade will shave reasonably evenly on both sides.
At this point im happy enough to use the knife and within 5-10 minutes notice slight dulling occurring. I get the light out on my phone and scan the edge again and typically there will now be light reflecting off the edge in areas that feel blunter than others. This typically happens more closer to the tip of the knife but will appear in sections of the blade. I have tried honing just the microbevel til the light fades as well as that plus the back beveling and it never stabilises. If i continue on the microbevel for too long it just thickens the edge without improving cutting ability and just makes the next sharpening job more time consuming on the knife.
From what I gather the angles im using are lower than what generally gets recommended but even at "normal" angles the same issues arise so I've continue doing what I'm doing so my edges at least remain thin and cut decently until I figure out exactly what is happening. I should also mention that at work we use poly boards that aren't perfectly flat so I havent ruled that out as a possibility yet. I am going to try another board tonight to see if that makes any discernable difference.
Lets say im about to sharpen a 61 rockwell ginsanko chef knife that is 50mm wide at the heel and 250mm long (similar approach and results with my carbon gyutos as well). I'm free handing and raise the spine of the knife about 5mm off the stone at the heel to set a bevel (this would be around 6 degrees per side?) And typically finish at like 12mm off the stone for the micro bevel (this would be around 13 degrees per side?). My terminology may be incorrect here but those are the angles im using anyway. I typically use back and forth or scrubbing strokes in initial shaping of the edge and move to heel to tip strokes in subsequent sharpenings and when I'm close to finishing a knife
(New knife)
- destress lightly on a flat soaked cerax 700 (or 320 in the case of severely dull knives)
-grind right side until edge stops reflecting light
-lightly destress twice on the same stone again
-grind the left side until the edge stops reflecting light
I pay attention here to whether one side has stopped reflecting light sooner than the other and by roughly how much quicker this process has occurred. As Japanese knives are generally assymetrically ground and sharpened often the right side will be finished much sooner than the left. It's at this point I'm unsure whether to:
-raise the angle on the side that took longer to prepare to account for the assymetry of the blade (and potentially lower the angle on the side that was prepared sooner) to keep the grinding times relatively similar per side
Or
-keep at the same 50/50 angle and grind more on the side that took less time to prepare so that the edge eventually moves closer to the side that originally took longer to prepare, eventually resulting in similar grinding times per side. (This process tends to involve a constant destress and prepare cycle keeping the number of passes per side needed to prepare each side in mind). This can take a while to even out in some cases
Whichever route I've opted for I now know for future sharpenings what angles are required for even grinding on each side. After that initial bevel setting or if I'm touching up that knife after use in the future the process is then:
-destress once lightly on the stone
-grind each side of the blade evenly until the light stops reflecting (This tends to happen rather quickly with decent 300-700 grit stones).
-I will typically make a bit of a slurry on the stone with a diamond plate or nagura and move to alternating heel to tip strokes trying to change the scratch pattern each time. These are made edge leading to reduce the chances of forming a burr (the slurry/mud helps with this). This may typically be about 8 or so per side. Blade slices well at this point and in the case of finer grit stones it may shave also at this point
(Although not important)
-clean off the stone or grab a finer polishing stone
-raise the angle to 13 degrees per side (or in the case of the assymetrically sharpened blade ~8 degrees one side and ~16 the other) and use alternating edge trailing strokes crossing the patterns again to reduce the likelihood of another burr forming. This is typically only around 2 each of heel to tip and tip to heel strokes on each side (In the case I decide to go with an 8k finishing stone I will usually use double these angles however typically I will use a 3000 grit stone). The blade will usually shave ok at this point
-use the same edge trailing strokes at my original shaping angle to "backbevel" and reduce the effect of any 'blunting' the micro bevel bas causes. This can be anywhere from a couple of strokes to like 15 per side. Blade usually shaves even better than previously (although i dont think I've ever been able to get tree topping sharp that people describe. Even my gold dollar straight razor that I use for shaving doesn't do that although I find it fine enough to do the job without any irritability)
At this point I'm pretty confident ive produced a wire edge here despite the apparent keenness. To elimimate it ive been playing around with:
- trying another light edge leading microbevel pass or parallel to the edge. I have also tried doing this with the original shaping angle. As the majority of my sharpening stones are friable waterstones its pretty easy to trash the edge with an edge leading pass without improving it. Using higher grit and harder stones help slightly.
-alternating an edge leading pass at shaping angle on each side on my norton fine followed by alternating trailing passes on a finishing stone (3 or 8k)
I have tried other stones and approaches but overall the blade has felt pretty similar in use at this point.
-There is no light reflecting on the edge, the knife feels to cleanly cut paper and can usually perform a 90 degree push cut on paper pretty easily.
-In the case of the assymetrically sharpened/honed blade it will typically shave at a lower angle on the side with the lower angle applied (generally the right side) compared to the other.
-The 50/50 blade will shave reasonably evenly on both sides.
At this point im happy enough to use the knife and within 5-10 minutes notice slight dulling occurring. I get the light out on my phone and scan the edge again and typically there will now be light reflecting off the edge in areas that feel blunter than others. This typically happens more closer to the tip of the knife but will appear in sections of the blade. I have tried honing just the microbevel til the light fades as well as that plus the back beveling and it never stabilises. If i continue on the microbevel for too long it just thickens the edge without improving cutting ability and just makes the next sharpening job more time consuming on the knife.
From what I gather the angles im using are lower than what generally gets recommended but even at "normal" angles the same issues arise so I've continue doing what I'm doing so my edges at least remain thin and cut decently until I figure out exactly what is happening. I should also mention that at work we use poly boards that aren't perfectly flat so I havent ruled that out as a possibility yet. I am going to try another board tonight to see if that makes any discernable difference.
