sharpening problem??

S

Slate

Joined
Feb 10, 2004
Messages
10
One of my standard sharpness tests is slicing through a sheet of newspaper or notebook paper. But I've been noticing that, depending on whether I'm slicing "with the grain" of the paper or not, I'll either get a nice clean slice or a ragged tear. Sometimes the blade will have trouble even getting past the edge of the paper--the paper will just wrinkle and cave in when I try to slice. Yet I can take the same blade and shave hair off my leg with no problem. I'm guessing that I'm missing something during the sharpening process. (I use a Sharpmaker and I make sure to raise a burr, etc, etc.) Any tips?
 
Try stropping, a wire edge can form and roll from side to side when cutting paper yet still feel sharp.
 
Another issue with paper slicing can be blade thickness. If you have a thick blade with a saber grind the paper folds up trying to get around the blade thickness.

When you cut paper you depend on the paper to not fold over, accordion, twist, or tear. Slicing away from yourself is sort of cheating, but it puts the paper in tension which makes things work most reliably. If you are pushing through the paper edge-on with no tension you are relying on cutting forces to push down the plane of the paper. If you push off-center or the paper is in some way assymetrical (or anisotropic) it will start to fold, accordion, twist, etc. Some paper can have a slick side and a rough side and this might give you trouble. As you observed some paper has a definite direction that the grain runs. If you cut across the grain there is very little to keep the paper from rolling. You might really need a straight razor to cut that paper cross-grain.
 
anisotropic: Describes a structure whose appearance varies with the angle of observation.

I had to look that one up Jeff.
 
If you're ever at a show with Sal Glesser at the Spyderco table make sure you ask him to show you show to shave paper with the spine of a blade. It puts shaving paper with the edge in a whole new perspective. ;)
 
Actually anisotropic describes a material whose properties are not uniform in all directions. For example a wooden board is pretty strong if you try and stretch it along the grain, but it splits pretty easy if you pull it apart across the grain. Any fibrous material where the fibers are not randomly arranged is likely to have different strength and different elasticity with the grain verses across the grain. A non crystaline solid like glass is pretty isotropic. A crystaline material can be electrically polarized or have mechanical properties that vary depending upon the orientation of the crystal lattice. The model in my head was of something like a thin mat of parallel reeds bound together by thread. It is easy to roll up the mat and hard to cut it cross-wise. If your paper looked like the mat on a microscopic scale it would roll over if you tried to cut it cross-wise without support. Lengthwise it would be trivial to cut it.
 
I did some stropping on a piece of cardboard last night and it made a noticeable difference. On the one hand, I'm not going to get too worked up about the paper cutting thing, because I've never had any trouble cutting things I need to--I'm happy with the performance of my blades. On the other hand, I think it's time to get serious about stropping--ditch the cardboard and get some leather and some of that goop to rub into it.
 
Slate said:
...I think it's time to get serious about stropping--ditch the cardboard and get some leather and some of that goop to rub into it.
Click to expand...

Good for you.

May I recommend one of the pre-loaded strop blocks from knivesplus? I recently got one and they're excellent.
 
When you strop be careful to either match the angle of your edge bevel or go to a slightly lower angle. Also use light pressure or you will tend to round off the edge. You want a fairly stiff strop.
 
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