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Post by Lord Cobol on Jun 25, 2013 18:12:17 GMT
Been doing some reading - trying to research my way up from crappy sharpening to merely mediocre - and I've come across wildly different opinions about the importance of mirror polish: - It's vital. The more polished the better. - It doesn't matter. Geometry is key. - It's a mixed bag, a double-edged sword. Helps or hurts depending on what you want to cut and how you want to cut it.
That 3rd theory works like this: all other things being equal (geometry, steel, etc) 1: High polish helps push-cutting, like shaving, because as you cut deeper into something, unevenness along the sides behind the edge creates drag. 2: High polish **HURTS** slice-cutting, like cutting tomato and many other kitchen tasks -- tiny saw-teeth in the edge work as, well, saw-teeth to dig in and get you started. I *guess* that polish helps as the slice progresses, but not as much as it hurts at the start. So, blades sharpened on a coarse stone might out-slice mirror-polish blades, but won't out-shave them.
Agree? Disagree?
If true, there could be odd consequences: - The famed AccuSharp jaggies might not always hurt as much as you thought (the fixed "V" angle might still suck, just not the jaggies). - Out of all the blades in your kitchen, the one that needs mirror polish most might be the cleaver (?) - The edge that looks better under a microscope might not really be better. - You might want to polish differently depending on blade curvature and the skill of the user (assuming that curve and/or skill mean a slicing motion, while a straight sword in the hands of a klutz will just be chopping into things).
*** Here's my big question: could you get (some of) the best of both worlds by going all mirror-polish on all of a convex edge, then lightly touching up just the extreme front edge with something a bit coarser ????? ***
Silly me. I was planning to get an unsharpened sword to practice sharpening on, double-edged so the edges could have different geometries, one "battle sharp" and one "scary sharp" (if I'm good). Now I need to do each geometry with two different polishes, so I have to search for a quad-edge sword :(
There's money at stake here, as I also try to *purchase* my way up from crappyness to mediocrity. Answers to the above might help me decide whether to buy goodies like a Spyderco Ultra-Fine bench stone and/or a strop.
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Post by Sir Thorfinn on Jun 25, 2013 19:44:18 GMT
My .02 You may get different opinions, but geometry is very important. Polish is as well, but IMO if you mirror polish to the edge, and get that scary sharp edge, it will still cut better than something left by an accusharp or jaggedy edged method...yes, the fine toothed edges assist in slicing, but once you get that sharp, jagged wont help much.
From a mechanical standpoint, once you get the edge to scary, its easy to change it slightly, and put a little toothyness into it by doing a few light strokes at an additional degree or two. The problem is to do that in any sort of controlled way, you need expensive tools.
Hows this though...I have a crappy 50.00 viking sword that I reprofiled and have one side hair popping sharp, and bottles are effortless. It cuts by gravity. I assume a good polish on a katana would do even better.
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Post by adamthedrummer on Jun 25, 2013 20:56:43 GMT
Well a smooth super fine edge will cut cleaner then a jagged edge, a little jaggedness might help bite into soft targets but the friction caused will kinda negate that, in theory. Imagine shaving with a jagged razor, tug tug ouch. :-)
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Post by Ulrich on Jun 25, 2013 21:47:06 GMT
-------------------------------- Disagree. A blade that has a grinding on coarse stones might do a better cutting job, but in fact it's not cutting but sawing. When it comes to the question which blade is the sharpest, I'd go absolutly for the technical measurement of the edge. There's no rule from 1-10 or stuff for sharpness, but the edge can be measured with high end measurement tools. The thinner it is, the sharper it is. The achievable thinness depends on the structur of the material, like the size of the martensit crystals. But away from mostly company or university owned measurement tools, I'd go at home only for hair popping=sharp, complete the hanging hair test=ultra sharp. That's not very scientific, but it works. And ja, if you've got the sharpest possible edge, the geometry will determine how deep the cut goes. So a supersharp edge in combination with a flat angle will do the best cutting job.
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Post by adamthedrummer on Jun 25, 2013 22:19:56 GMT
Indeed...but then the old problem of thin edge easier to damage. So where to draw the line?:-)
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Post by willhart on Jun 25, 2013 22:27:03 GMT
Ok I wrote a big long answer, but apparently it didn't get posted. This is my opinion and I'm not that experience as others.
It may be easier to dull and edge with a softer back on the sandpaper, but you can dull it the same with the sand paper on a hard block. It's all about technique and consistancy/practice.
Using a softer back usually is to give it a natural convex edge.
I've used Arkansas type stones, the cheap tri-hone at Home Depot and real arkansas stones and due to how hard they are, I can see how you can clog them. Compared to Japanses Water Stones, you won't have that problem, and Japanese water stones take off metal faster. The downside is the wear down faster. You can buy cheaper waterstones from Amazon or the dual sided ones 220/1000 for about $30. But note the 220 side is really for reshaping or taking of a lot of metal.
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Post by willhart on Jun 25, 2013 22:32:21 GMT
Another thing is the lower grit you use to sharpen, the better it will saw due to the teeth, but those little teeth will break off faster and your edge will dull or roll faster too.
The higher up in grit you go the less little teeth you have and it should stay sharp longer.
Now depending on what you're cutting you may or may not notice, but I can tell a big difference in how long my kitchen knives stay sharp when I use my belt sander to sharpen them, vs an accusharp. The accusharp does make them sharp, not razor sharp like the belt sander, but the sharpness doesn't last long.
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Post by willhart on Jun 25, 2013 22:34:14 GMT
Sorry for the spamming of replies. Lord Cobol, would you mind replying to your thread instead of editing your original post? I don't want to reread through it again and try to find out what you've added since the last time I read your post
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Post by Ulrich on Jun 25, 2013 23:11:51 GMT
--------------------- Ja, that's right, bro.
---------------------
---------------------- I wouldn't draw it anywhere. The technical sharpness can be the same, but on a heavy niku combat blade the edge damages wouldn't have the same negative effect as on a highly optimized cutting blade. When a cutting blade is thin and supersharp it depends strongly on the individual skills of the user not to ruin it, but some damage on the edge is always be given.
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Post by Lord Cobol on Jun 25, 2013 23:16:33 GMT
@wilhart - I haven't edited it. But I do have another thread going with different questions and I see your reply there. @wilhart - The accusharp-edge not lasting as long is interesting. adam - the shaving example fits with the theory I mentioned at the start. Shaving is the classic example of NOT slicing, so smoothness should help (both front and behind the edge) and jaggies would not help. Re my "big question" ("could you get (some of) the best of both worlds by going all mirror-polish on all of a convex edge, then lightly touching up just the extreme front edge with something a bit coarser ?") saying "a bit coarser" was poor wording. I was thinking "a bit coarser than what put the mirror polish on", which would still be "fine" by most standards. Anyway, picture a mirror smooth convex edge with just a small fraction of a milimeter of kinda-fine-but-not-mirror at the exteme edge. Has anybody here even tried that?
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Post by Ulrich on Jun 25, 2013 23:37:04 GMT
The grain of the stones you need for mirror polish is much higher than what you need for just a hair popping sharp edge. So it's no problem to have a mirror polish and a saw or just useful sharp edge. I often heard that cutting feels more comfortable when the edge is more saw-like (under a microscopic view). Maybe I've done the same experience, but I cannot really say that, cause I havn't take a microscopic view on the edges I've used for slicing.
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Post by adamthedrummer on Jun 26, 2013 0:42:35 GMT
Probably a matter of personal preference in the end, cutting style, sword type, experimentation will be the ultimate answer. :-)
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Post by Sir Thorfinn on Jun 26, 2013 0:57:21 GMT
Yes, you can add a little toothless to the final edge, but that takes years of practice or precision tools...
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Post by willhart on Jun 26, 2013 4:10:27 GMT
Oops my fault Cobol, I got confused. Your posts seemed so similar I thought you were editing the post, that's why the looked different Here is a good post from another forum that shows a magnified view of an edge for comparison. forum.grtc.org/viewtopic.php?f=9 ... t=15#p6033 You can see the difference as you go up in grit and then the final strop. Going up in grit in sharpening isn't for looks only. It will help keep the edge sharper, longer.
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Post by Lord Cobol on Jun 26, 2013 7:42:01 GMT
Yes, I read that thread a while back, and just re-read. Starting about halfway thru it is a good exposition of the "more polish is better" theory. But I have also seen people who claim to be expert expound two different theories. My hybrid guess/theory is that polish behind the edge is always good; polish on the edge too is good for shaving, chopping into things, etc; but that too much polish on the edge can be bad for cutting things where you have to slice (tomato, rope, etc). Reduced durability of an un-smooth edge is a concern; increased surface area making it more vulnerable to rust shouldn't be an issue if you are good about your monthly cleaning & oiling. Or if you live in S California like I do
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Post by Lonely Wolf Forge on Jun 26, 2013 12:50:08 GMT
as far as im concerned geometry accounts for roughly 80% of cutting ability as far as swords and cleaving through flesh ext. a poor geometry sword with an ultra hair popping muramasa edge still wont perform worth a damn if the geometry prevents it from cutting, this is why secondary bevels suck, the edge can be super sharp, but the bevels create an impact and bat away the target before the edge can even have time to cut. this is why you see some guys who are able to cut tatami and such with blunt swords and good technique, though the sword is blunt, it has proper geometry and paired with good technique they are able to make cuts. when it comes to swords in my opinion, youcant sharpen your way out of poor geometry. Now lets assume 2 blades of equal geometry, the one that is polished and refined better, is going to be sharper and cut better than one thats left jagged. IMHO. this is shown to be true when im making my blades. ill hit them with a low grit belt sander, do a test cut and it will rip/tear the paper, then ill sharpen with medium grit, repeat the test, and it will literally saw right through but wont slice, once i use the fine grit belt, then polish with a strop and rouge however, the blade will SLICE the paper without ripping/tearing/gouging. so the saw style edge might cause more damage, but its not going to "cut/slice" as well.
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Post by L Driggers (fallen) on Jun 26, 2013 14:18:09 GMT
There is nothing wrong with a secondary bevel, I'll put my up agianst anything else. Just alot of hype, yes a good edge can make up for bad techique. But learn to use your tools right. I have no touble slicing paper with my edge, can even do the slice in the air trick.
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Post by Lonely Wolf Forge on Jun 26, 2013 15:32:00 GMT
but can you get silent cuts on empty bottles with a big fat 45 degree secondary bevel? no matter how sharp it is, its not going to happen
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Post by aussie-rabbit on Jun 26, 2013 15:42:46 GMT
Here is the youtube showing the edges under the microscope -
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Talon
Member
Senior Forumite
Posts: 2,554
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Post by Talon on Jun 26, 2013 15:43:43 GMT
viewtopic.php?f=3&t=3412The secondary bevel vs apple seed debate has already been covered many times,i'll go with Tinker on this subject.
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