Is it possible to oversharpen a knife?

C

Clint Simpson

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Nov 13, 2001
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"Fill your bowl to the brim and it will spill. Keep sharpening your knife and it will blunt."
Lao Tzu

Is it possible to oversharpen a knife? I'm not taking about making a mistake and having to repair the damage (blunting) to the edge. I'm taking about going so fine that the edge has a lesser cutting ablity. :confused:

After sharpening my knife on 400 grit wetdry paper the knife could almost melt the hair off my leg (more room than arm). But after using 800 grit paper, it would scrape dead skin(meaning: angle was too high) but not cut hair. If used at a lower angle it would glide off and still not cut.

What is going on and WHY?
 
Yes and no. ;)

You can reach the point where the edge is too polished. For example, when I sharpen an edge to cut rope, I get awesome performance at 150 or 220 grit, then the performance gets worse and worse up to about 800. At 800, it'll melt its way through- I've progressed from sawing the fibers with microserrations to slicing them.
 
Perhaps in the time of Lao Tzu this was literally true, but I would expect that the sharpening implements or your technique would be limiting, but not counterproductive.

I think that passage is just trying to emphasize that you can only do so much before your actions become counterproductive. Kind of like: "Too many cooks spoil the soup," or the 20-80 principle. The Tao Te Ching is really intended to be a guide for life, not sharpening instructions :)
 
S2nd said:
The Tao Te Ching is really intended to be a guide for life, not sharpening instructions :)
Click to expand...
Sorry, sorry, I was confusing in my post

I used Lao Tzo as a reference. The real issue is my own experence.
400 grit=shave hair
800 grit= no shave hair

Why and more importantly HOW?

The problem of being well-read/educated (in the abstact) is knowing that anything tends to relate to something else on some level. The trick is knowing how far to take it to be useful without going to far.

Wait! I just realized, that is what Lao Tzu was talking about :rolleyes:
BTW, I'm not complaining just clairifing
 
Silly me! :D

My only thought is that the edge may be getting rounded if the paper gives too much.
 
I would imagine that you produced a very small burr or wire edge on the 800 grit that you didn't cut off properly. Read this thread: http://www.bladeforums.com/forums/showthread.php?t=336624
and do exactly what Vampyrewolf says. 800 grit is actually still a fairly rough grit so I doubed that you overpolished your edge. Which also means, that producing a burr at this grit is actually quite easy if you are working on edge. Besides polished edges usually perform better in push-cutting and shaving is a push-cutting action.

As far as the title of your thread is concerned. Barbers would indeed say that it is possible to over-hone a razor. Due to the very small included angle you can produce a large wire edge on a razor which you can not strop off. Once you try to strop the wire edge it literally tears off. Similarly it is possible to over-hone a chisel or a knife by working to long exclusively on one side which results in an overly large burr which again is very hard to cut off without tearing it off, leaving a ragged and dull edge.
 
People have touched on most of the problems with extensive sharpening. Let me add a touch or two.

If you sharpen at somewhat obtuse angles (like 20-degrees per side or higher) you ability to shave may depend on having a burr along the edge which is thin and weak, but cuts off hair. Continued honing is likely to remove the burr which reduces shaving ability and also you may slightly round your edge which further increases your edge angle. If you do a very clean job of sharpening at this angle, which is hard to do with sandpaper, you can get a burr free edge that is sharp, but it is not a great shaving edge. Also as you polish an edge like this it will slice less effectively. When you have an obtuse edge it slices much more effectively with a rougher, microserrated edge finish.

If you sharpen at an acute angle you can get burrs the roll over or tear off. You need to hone edge forwards for a bit at a more obtuse angle to remove the burr and go back to sharpening. For this kind of edge you will definitely have a better shaving edge if you work with 1500 grit or finer. You need to work with very light pressure as you get to the end of honing. You need to avoid rolling or rounding your edge. I like ceramic hones since they produce a fine edge and are very smooth and hard. I find less chance to round an edge with a ceramic hone.
 
Clint Simpson said:
400 grit=shave hair
800 grit= no shave hair
Click to expand...

I shave my face with a straight razor and it comes off an 8000 grit water stone and then gets stropped with 0.5 micron compound and then polished on a plain leather strop. The grit isn't the problem.
 
When your bowie looks like the nib of a fountain pen, you've sharpened too much! ^-^ Aside from what was mentioned about the burr, it kind of depends on what you consider sharp... a good sawing sharp rope cutter might not cut rope so well anymore if you sharpen it to a good push-cut edge.
 
These responses deal with polishing the bevels. Sharpness really is a function of the angle of these bevels to each other. If you oversharpen - grind to an angle that is too acute - the edge will deform in use and, in effect be blunt. So the original quote was actually a good one.

I polish the bevels on my own knives with an 8000 grit water stone. I've found that going beyong that doesn't provide enough improvement to be worth the work, although I do have a 12,000 grit that use occasionally when I have time.
 
If the sharpness test that you are failing is shaving, the problem is not too low a honing angle. I just looked at my Dovo straight razor and it is honed to 7-degrees per side. In addition it is deeply hollow ground so there is not much metal behind the edge either. Razor steel is not all that hard either, it is just fine-grained. I doubt that you could get your edge much below 12-degrees per side even if you tried.
 
What Jeff said!

Besides, modern blade steels actually support surprisingly acute angles, Something that Lao Tzu probably didn't have access to.
 
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