Sharpening: Shaves one way, not the other!

WadeF

WadeF

Joined
Apr 12, 2000
Messages
2,116
Here's a question. Usually when I sharpen my knives I can get them to easily shave my arm hair, but usually it only shaves in one direction! Any ideas? Could it be there is still a burr and it's catching the hair on one side and passing over the hair on the other?
 
Try holding your arm the other way. It always works for me. :D

If that doesn't work, a little light stropping on a leather hone will usually do the trick.
 
WadeF,
Steve's right. I used to have that same problem. You can solve it by making a couple of real light passes on either side of the blade on your stone with the blade at a 35 or 40 degree angle. I Sharpen my knives with sandpaper held on a mousepad and take the edge down to 1000 grit, sometimes as far as 2000 grit. I've not had that problem this way.
 
Sounds like your edge has rolled to one side. Try using a kitchen steel or stop to straighten it.
 
I had the same sharpening problem, I solve this by using my stone a bit like a steel, ie I take the stone at an angle of about 20-25 degree from vertical and make a few light passes on both sides like if it was a steel. I prefer to use my stone rather than a real steel because, first a don't have a steel :D (but I should get one finally for my kitchen knives), second because the small rails on it will give you an edge with microscopic serrations (take a magnifying jeweler's scope and it's there) which gives kitchen knives an extra biting edge to cut meat and stuff, but not a real polished edge... though I have to admit that a steel gives good (maybe the best) results to get a "field" edge, I mean a more versatile edge to cut through fibrous materials. Another solution is to give your blade some stropping on leather with an adapted polishing compound, but I find it don't give great results on highly hardened blades (I'd say over rc 58).
Now you have choice :)

-- Xavier.
 
The strop will help a lot. You can strop on cardboard on a firm surface if you don't have leather, though the inside of a belt on a firm surface will work too. Stropping compound is nice but not necessary for edge straightening.
By laying the knife flat on the strop & just putting pressure toward the edge as you strop, you can get repeatable results & good edge alignment. It's the same technique barbers use for straight razors.
This will also give you a microscopic convex edge which will make the edge stronger & that last bit sharper.
 
Originally posted by slices
The strop will help a lot. You can strop on cardboard on a firm surface if you don't have leather, though the inside of a belt on a firm surface will work too. Stropping compound is nice but not necessary for edge straightening.
By laying the knife flat on the strop & just putting pressure toward the edge as you strop, you can get repeatable results & good edge alignment. It's the same technique barbers use for straight razors.
This will also give you a microscopic convex edge which will make the edge stronger & that last bit sharper.
Click to expand...

I do have a leather strop. I have experimented with it a few times. I don't have any compound for it and have just been using the bare leather. How much pressure should be applied when stropping? Also I have learned you can find the stropping angle by moving the blade forward and tilting it up until the edge bites and then draw it back. Is this how most of you go about it? :)
 
The burr is weak metal that you want to get rid of. Using a steel or stropping without abrasive will leave you with a weakened edge. The best approach is to hone the burr off then reset the edge. After you do this stropping may be helpful if you want to be able to shave.

A burr forms when you remove a lot of material at a low angle. It tends to happen more if you hone with edge-trailing strokes (stropping motions) or if you work one side of your blade and then the other side. Even in ideal circumstances you will tend to get some burr for anything other than a trivial amount of sharpening.

To remove a burr you need a sharp-cutting medium-fine hone. I like to use a diamond hone, but any hone that is not too fine will probably work, just make sure that it is not loaded up with debris. I periodically scrub my hones with a brush using water and abrasive sink cleanser. Now use some light edge forward honing strokes with your edge super-elevated to about twice your normal finishing honing angle. For example if you back-bevel your edge using 15-degrees per side and finish using a few strokes at 20-degrees per side then you should debur using an angle of 40-degrees. Your strokes should alternate from side to side every stroke. Don't go too hard since you are making your edge more obtuse at this step.

After maybe 5 strokes per side your burr should be gone. Try and feel it. Once it is gone, go back to your normal finishing angle (say 20-degrees) and do about as many alternating strokes at this angle as you did for deburring (use equivalent light pressure). At this point you can strop if you like to. This procedure will give you a sharp and durable edge.
 
Originally posted by Jeff Clark
After maybe 5 strokes per side your burr should be gone. Try and feel it. Once it is gone, go back to your normal finishing angle (say 20-degrees) and do about as many alternating strokes at this angle as you did for deburring (use equivalent light pressure). At this point you can strop if you like to. This procedure will give you a sharp and durable edge.
Click to expand...

Alright, this makes sense. :) Now, I have an EdgePro with 180, 220, 320, and I think 620 or something around there stones. Which would you recommend? The 320? 220? Also when you say 5 strokes per side I assume you'd do 1 stroke, flip, do another stroke, flip, etc? :)
 
Shaving on one side but not on the other is a sign of a rolled edge. This will not be removed by steeling, and stropping is really ineffective at removing it as well. The rolled metal needs to be cut off with edge-into honing, if possible not on rods but on wide hones. It can be done with rods but the force should be minimal as the contact area is so low that great pressures are generated easily and will act to steadily deform the edge.

-Cliff
 
There are a lot of variables that can confuse grit comparison by numbers. With a diamond hone a 600 grit would be ok. With most other hones either 220 or 320 would be about right. Scratch the hone with your finger nail. You want to use a hone that feels like it is sanding your nail, but doesn't have a lot of drag. You don't want it to feel smooth like an Arkansas stone.

As Cliff mentioned, a narrow hone (like a rod) applies its force to a small edge area. This will tend to bend the burr to the other side rather than cut it. So apply very light pressure and maybe 8 strokes per side total. You are correct that you alternate sides right-left-right-left etc.
 
It's easy to mount DMT diamond hones on an edge pro. You'll need a piece of brass or steel tubing 3/8 " by 3 ". Just unscrew the round knob handle, remove the tubing that it comes with, & replace it with the above. That will allow you to tighten up a diamond hone with no problem. The main benifits with 'em are that they always stay flat & they remove metal fast. Check your Edgepro stones & lap 'em flat if need be, flat stones are important.
But as already noted, the real problem is the edge is out of alignment. If you just do light push cuts & want an extremely sharp edge, then strop the rolled edge into alignment. A razor will roll it's edge just by feeling the edge with your thumb. It's basically an aligned burr. That's the kind of edge you will have if you finish by stropping it into alignment.
Honing will strengthen the edge if you remove the burr completely, but you still need to be sure that the edge is in alignment when you finish. A 20x or preferably 30x magnifying glass will help a Lot! Radio Shack has an inexpensive 30x self lighted microscope that is great for this, catalog #63-851.
If you don't get a scope, you still can learn to feel the burr. Then remove it using the techniques from Jeff & Cliff.
Ask yourself what you will be using the knife for & set the edge up accordingly.
I carry a knife which will cut hair without touching the skin. If I were to use it for cardboard or wood, even once, I'd have to resharpen it. I use the knife in my other pocket for everyday work. It has a more durable edge.
When you ask which stone should you use on the Edgepro to remove the burr, that's up to you. Coarser stone creates a more agressive edge, finer stone, more polished edge. You may want to read the manual again on page 9 where it explains feeling for the burr, removing it, and finishing the edge. The technique you described for stropping works fine Wade, so does the one I described. Try each & see which gives the best results. Different knives will respond to different techniques. But to really polish the edge, not just align it, use stropping compound rubbed into the strop.
Here are some tables that may help you to cross reference between the different grits & classes of sharpening media. But the answer is really more about getting the edge aligned than what grit is used.

http://www.ameritech.net/users/knives/grits.htm

http://www.gemsociety.org/info/chmesh.htm
 
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