Cliff Stamp
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- Joined
- Oct 5, 1998
- Messages
- 17,562
I had been intending to look at this in detail ever since I put up the review of the OK-45 from Kyocera, but never got around to picking up the necessary sandpaper. The weekend while looking for something else I spotted a small pack of SiC sandpaper in three grits for $1, which reminded me of the ceramic blade and so I now had the means to look at its sharpening. As noted in the review, I had damaged the edge with some attempts at sharpening, mainly with rods, and when I finished the blade could just barely slice paper and was thus at just a few percent of the initial sharpness. I can not imagine actually wearing it to this dull a state just cutting food in the kitchen, it would take many years.
I made a series of hones cutting small strips of the sandpaper and attaching them to 1/4 inch thick cardboard. I did this because I wanted the abrasive to give a little so that the angle tolerance would be low, as my freehand sharpening skills are not that high. The sandpaper came in 240, 320 and 400 grit, and there was enough of it to make 28 of the strips for each grit, which were about 2 cm wide and 6 cm long. After each session of honing the sharpness was tested cutting paper a few ways, slicing up a roll of 100% cotton (the sleeve of a shirt), and checking it under magnification to see how the edge behaved. The "hones" were not wore out after the session, so that package of sandpaper had enough material for more than 50 honing sessions (more than one lifetime for one blade).
Using the 240 grit strip I gave the blade ten passes per side edge trailing, and then 10 per side alternating. The edge was full of chips of up 1mm deep [x20 mag]. The blade didn't see any increase in paper slicing ability, it could only slice photocopy paper at an angle, and tight to the point at which I was holding it. On the fabric, it took two complete passes of the blade using heavy pressure. For comparison, when freshly sharpened it only took about 25% of the blade to make a complete cut. The blade virtually would go right though the fabric almost in a press cutting motion.
Onto the 320 grit strip, the edge was given 20 strokes per side and then 10 per side alternating, the chips were now cut in half. The paper slicing ability took a huge jump as it cuts very smooth on an angle, and could cut straight down on a slice but needed a tight close grip, about a half and inch or so from the edge contact to where the paper was held fixed. The fabric slicing ability also took a huge jump and now only needed about 3/4 of the blade length.
The 400 grit paper was then used for the same amount of honing. The edge now went back to having similar chips as in the 240 grit honing, and were more frequent. However the paper slicing ability got smoother again, and the fabric was down to needing about half a blade length. I then tried some fifteen micron SiC paper that I bought from Lee Valley, and it didn't improve the cutting ability, but the finish changed. The edge got smoother overall, the chips were cut in half and the frequency much reduced.
I then finished up with some five micron SiC paper, also bought from Lee Valley, and again used the same number of honing passes. The edge finish got a little smoother under magnification, but the paper slicing ability went up significantly and now the blade was approaching the ability to push cut straight down, start a cut on a draw and then turn it into a smooth push. The fabric was now only taking about 25% percent of the blade length and was approaching a push cut. The edge was now also just barely starting to shave.
I then used the blade in the kitchen on carrots, meats and the like and the performance was very high. Easily in the same class as what you could expect from production steel knives, and easily sharp enough to cut any food with the exception of things like over ripe tomatoes.
Just to see what effect it would make , I later on used a strip of 0.5 micron CrO paper in the same manner as in the above. To my surprise the finish improved significantly, and the blade started to gain shaving ability quite rapidly and after a few sessions of 20 passes per side, it was able to shave decently well (I was just working on one section of the blade to speed things up, there is a huge jump from 5 micron SiC to 0.5 micron CrO which slows the honing down). The blade was now cutting the paper very smooth, with no loss of fabric slicing ability. The edge was approaching a smooth straight line under the scope.
I don't quite understand the behavior of the edge finish, it seemed almost random and didn't correlate well to the cutting ability. I then took a steel blade (TAC-11) and ran it through the same series of hones. The edge improved in a smoother manner as the grits were progressed through. The steel blade was also much sharper at any given grit. After the five micron paper it was shaving quite smoothly.
In short, 400 grit SiC sandpaper, which you can find almost anywhere, will put an above average edge on the ceramic blades from Kyocera , there is no requirement for expensive or hard to find hones. This edge can be refined with higher grit sandpaper, the automotive section of most hardware stores will carry it up to 2000 grit, and to get the finest shaving edge, just as with steel blades, you will want to finish with CrO. Based on the fact that the CrO will sharpen it, it seems likely that waterstones might work as well. I intend to look at this later on, as well as using the fine diamond pastes from DMT.
Ref :
http://www.physics.mun.ca/~sstamp/knives/ok_45.html
-Cliff
I made a series of hones cutting small strips of the sandpaper and attaching them to 1/4 inch thick cardboard. I did this because I wanted the abrasive to give a little so that the angle tolerance would be low, as my freehand sharpening skills are not that high. The sandpaper came in 240, 320 and 400 grit, and there was enough of it to make 28 of the strips for each grit, which were about 2 cm wide and 6 cm long. After each session of honing the sharpness was tested cutting paper a few ways, slicing up a roll of 100% cotton (the sleeve of a shirt), and checking it under magnification to see how the edge behaved. The "hones" were not wore out after the session, so that package of sandpaper had enough material for more than 50 honing sessions (more than one lifetime for one blade).
Using the 240 grit strip I gave the blade ten passes per side edge trailing, and then 10 per side alternating. The edge was full of chips of up 1mm deep [x20 mag]. The blade didn't see any increase in paper slicing ability, it could only slice photocopy paper at an angle, and tight to the point at which I was holding it. On the fabric, it took two complete passes of the blade using heavy pressure. For comparison, when freshly sharpened it only took about 25% of the blade to make a complete cut. The blade virtually would go right though the fabric almost in a press cutting motion.
Onto the 320 grit strip, the edge was given 20 strokes per side and then 10 per side alternating, the chips were now cut in half. The paper slicing ability took a huge jump as it cuts very smooth on an angle, and could cut straight down on a slice but needed a tight close grip, about a half and inch or so from the edge contact to where the paper was held fixed. The fabric slicing ability also took a huge jump and now only needed about 3/4 of the blade length.
The 400 grit paper was then used for the same amount of honing. The edge now went back to having similar chips as in the 240 grit honing, and were more frequent. However the paper slicing ability got smoother again, and the fabric was down to needing about half a blade length. I then tried some fifteen micron SiC paper that I bought from Lee Valley, and it didn't improve the cutting ability, but the finish changed. The edge got smoother overall, the chips were cut in half and the frequency much reduced.
I then finished up with some five micron SiC paper, also bought from Lee Valley, and again used the same number of honing passes. The edge finish got a little smoother under magnification, but the paper slicing ability went up significantly and now the blade was approaching the ability to push cut straight down, start a cut on a draw and then turn it into a smooth push. The fabric was now only taking about 25% percent of the blade length and was approaching a push cut. The edge was now also just barely starting to shave.
I then used the blade in the kitchen on carrots, meats and the like and the performance was very high. Easily in the same class as what you could expect from production steel knives, and easily sharp enough to cut any food with the exception of things like over ripe tomatoes.
Just to see what effect it would make , I later on used a strip of 0.5 micron CrO paper in the same manner as in the above. To my surprise the finish improved significantly, and the blade started to gain shaving ability quite rapidly and after a few sessions of 20 passes per side, it was able to shave decently well (I was just working on one section of the blade to speed things up, there is a huge jump from 5 micron SiC to 0.5 micron CrO which slows the honing down). The blade was now cutting the paper very smooth, with no loss of fabric slicing ability. The edge was approaching a smooth straight line under the scope.
I don't quite understand the behavior of the edge finish, it seemed almost random and didn't correlate well to the cutting ability. I then took a steel blade (TAC-11) and ran it through the same series of hones. The edge improved in a smoother manner as the grits were progressed through. The steel blade was also much sharper at any given grit. After the five micron paper it was shaving quite smoothly.
In short, 400 grit SiC sandpaper, which you can find almost anywhere, will put an above average edge on the ceramic blades from Kyocera , there is no requirement for expensive or hard to find hones. This edge can be refined with higher grit sandpaper, the automotive section of most hardware stores will carry it up to 2000 grit, and to get the finest shaving edge, just as with steel blades, you will want to finish with CrO. Based on the fact that the CrO will sharpen it, it seems likely that waterstones might work as well. I intend to look at this later on, as well as using the fine diamond pastes from DMT.
Ref :
http://www.physics.mun.ca/~sstamp/knives/ok_45.html
-Cliff
