I have an 800 grit waterstone I bought at the local woodworking shop. It was quite smooth when I got it, but after lapping it a couple of times, it feels quite coarse. I also have a coarse/fine India stone from Norton. My question is regarding the grits of the 800 and Fine India. The orange fine India seems to give a sharper edge than the lapped 800 grit stone. I tried sharpening my BM TSEK w/ slack sandpaper, then finishing with the Fine India or the waterstone. The India seems to give a sharper edge. From what I've read, the waterstone has the finer grit, so what's happening? Looking at the micrographs in Leonard Lee's book on sharpening, the 800 grit looks more coarse than the India, and this is reflected in the edge I'm getting. Do the waterstones cut with an effectively coarser edge for their grit, or do I just need to clean the India? Even if I do need to clean it, I like the edge it produces better, and it lasts longer.
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Sharpening Info Needed w/r Waterstones
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The waterstones are graded by the Japanese Industrial standard which produces different grit numbers than the U.S. system (also two different grading methods... the older sedimentation method is slightly coarser than the newer electrical method) and their grits are coarser than our grits but also go much finer.
800 grit JIS is 14 microns +/- 1 micron, meaning half the particles will be between 13 and 15 microns with 97% larger than 9 microns and 97% smaller than 31 microns. Some of the better manufacturers may grade their product more tightly than the standards require and have fewer stray oversized or undersized particles, but 14 microns is what they would be shooting for at 800 grit JIS (which would be closer to 700 grit US) 1,500 grit US would be about 4000 grit Japanese and have 3 micron particles.
Here is a table showing the micron size and error ranges for JIS grits (newer system) http://members.cox.net/~yuzuha/jisgrits.html
Here is another table that shows a rough comparison between US, European and JIS grits with some examples (i.e. green chrome rouge etc.) http://users.ameritech.net/knives/grits.htm
800 grit JIS is 14 microns +/- 1 micron, meaning half the particles will be between 13 and 15 microns with 97% larger than 9 microns and 97% smaller than 31 microns. Some of the better manufacturers may grade their product more tightly than the standards require and have fewer stray oversized or undersized particles, but 14 microns is what they would be shooting for at 800 grit JIS (which would be closer to 700 grit US) 1,500 grit US would be about 4000 grit Japanese and have 3 micron particles.
Here is a table showing the micron size and error ranges for JIS grits (newer system) http://members.cox.net/~yuzuha/jisgrits.html
Here is another table that shows a rough comparison between US, European and JIS grits with some examples (i.e. green chrome rouge etc.) http://users.ameritech.net/knives/grits.htm
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yuzuha's post is very informative.
I'll add that it is not uncommon for a stone to become "rougher" after lapping it. New they are kinda smooth anyway, and as you sharpen them the surface still kinda rounds over or blunts. When you lap them you clear out all of this "smoothness" and expose a nice roughened surface. A newly lapped stone will cut quicker and rougher, and a sit wears in a bit it will cut slower but produce a finer edge.
If you liek the smoothness of your india stone, then use that! Don't mix the means with the end. Use whatever you need to get the edge you want.
If you are looking for an even finer edge, try a 6000 grit watersone after that india stone. Of course you'll really be optimizing the blade for push cuts at this point though.
I'll add that it is not uncommon for a stone to become "rougher" after lapping it. New they are kinda smooth anyway, and as you sharpen them the surface still kinda rounds over or blunts. When you lap them you clear out all of this "smoothness" and expose a nice roughened surface. A newly lapped stone will cut quicker and rougher, and a sit wears in a bit it will cut slower but produce a finer edge.
If you liek the smoothness of your india stone, then use that! Don't mix the means with the end. Use whatever you need to get the edge you want.
If you are looking for an even finer edge, try a 6000 grit watersone after that india stone. Of course you'll really be optimizing the blade for push cuts at this point though.
Cliff Stamp
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Crayola said:
This isn't very pronounced with most waterstones due to the nature of the bond and the speed at which they break down. They only way this is a real issue is if you lap with such a coarse grit you actually do macroscopic damage to the surface of the stone, lap a 800 grit stone with beach sand for example will leave large gauges in the surface which will produce a irregular finish.
-Cliff
Fine India and most certainly 800 grit waterstones are actually really coarse. They are meant to clean up and re-cut an edge that doesn't have major chips in it (though even small chips can be removed with an 800 grit waterstone). At this grit level it is really not so important how fine the edge is. Cutting speed is far more important. For a final edge you should be using something in the 2000-10000 grit range (japanese standard). Except if you are mostly cutting rope or bread were a really coarse edge might be beneficial. But again, how fine the stone leaves the edge is less important for those applications.
I lapped the stone w/ 100 grit SiC sandpaper backed by a worn out DMT stone. I like the finish it leaves on a couple of kitchen knives, but want something finer for my work knife. I was thinking of getting a 4000 grit stone and using the two together. 6000 is kinda expensive, and I dont see a need for something that fine for my knives. I have a couple of chisels, but I have to get a lot better at sharpening them before a stone that fine will help.