In theory it should work, but why not in practice?

D

DocNightfall

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Nov 20, 2006
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I had learned to sharpen on sandpaper last week and I was hoping to discover some more low-cost sharpening alternatives. So as an experiment, I cut a strip from an old leather belt, put it down on a flat marble counter top, and smeared a layer of cheap minimally abrasive metal polish on the leather. I spread the metal polish thinly and evenly then left it to dry. (On a tangent: does anybody know the particle size in microns of garden variety metal polish?)

About fifteen minutes later, it was completely dry and I set to work with my el cheapo strop. About fifty strokes per side on an old carbon steel utility knife significantly improved its push-cutting performance.

So I kept going. I stropped about fifteen minutes per side, making sure to maintain light pressure and a constant low angle, then I tested again.

Push cutting performance didn't improve. In addition to that, the edge had lost its aggression. It push cuts copy paper and shaves well (I was even able to whittle a coarse hair one time), but now I can run my fingertips up and down the edge with more than light pressure without hurting myself! Now when I use it to cut stuff, it actually cuts less efficiently, because adding a slicing motion to the cut doesn't speed things up a great deal compared to just push cutting.
 
Stop when it's sharp.
Your angle may be too acute, or you may be pressing too hard, too.
 
DocNightfall said:
How do you know when to stop?
Click to expand...

Hope this might help. I have used my leather strop long enough that it has become dark black and very shiney. After I finish on the stones, I always have some degree of a burr depending on the steel. If I hold the strop just so, in the light, I can see which side the burr is on by the way it disturbs the shiney black surface of the leather. Ex; in one direction, the burr side of the blade will rough up the shiney surface and that tells me that is the burr. In the other direction, the blade will replace the shine and that tells me no burr. I just work until I have a shiney surface in both directions.
 
Even in theory it doesn't work. The leather always wants to wrap around the front of the edge (what is there to stop it?). If you only strop a little bit you will only round the edge off a little (and mostly straighten, debur, reduce the width of the edge). Stropping on anything that is not hard and stiff will eventually round off the edge.

To visualize the situation on a larger scale imagine stropping on foam rubber. The foam rubber does not form a graceful curve under your blade and extending out behind the edge as you strop. It wants to pop back up rather steeply right where your edge leaves off. This causes it to rub upwards across your trailing edge. To improve the situation imagine that you laid a sheet of mylar about as stiff and thick as an audio CD on top of the foam rubber. As you stropped on that surface it would form a graceful arc against your blade and edge. You could strop on that indefinitely without dulling your edge.

So try something smoother and stiffer than leather if you are going to strop for a long time. Otherwise strop only briefly. You could look for a mouse pad that has a stiff and smooth upper surface.
 
I see. I thought that keeping a low angle and using very light pressure would avoid that sort of problem. So would it perhaps be better to smear my metal polish on a piece of cardboard and strop with that? I'm referring to the kind used for backing on legal pad. I've stropped on cardboard before to remove burrs, but without any abrasive added to the surface.

What kind of surface could I strop on indefinitely without the edge eventually getting rounded?
 
I'm still learning how to hone with leather. I've poked around the web allot and came up with a few sites that seem to offer some good advice. This is one of the best I've found:
http://www.handamerican.com/lhone.html

Gary
 
To strop indefinitely you would need a very flat and stiff surface. For what you are trying to do I have used plastic viewgraph material (I think it is polyester, like Mylar) over the top of a short stack of 20 pound copy paper on top of a good hard desk. Since you are using an added abrasive you don't need a rough abrasive "strop". A smooth one will give you a better result. I use diamond paste on top of the viewgraph material.

Maybe you should just give up the notion that you should strop for long periods of time. The only reason that people do that is to put a convex edge on a blade. It is not the normal path to a razor sharp edge. If you just want a razor edge do a good job of honing with flat hones (edge-forwards rather than the edge-trailing stropping direction) then do a brief interval of stropping (probably only 5 or 10 strokes per side--alternating sides with each stroke). Be sure that you debur before you start to strop or you may just end up with a weak edge.
 
Lest I forget: Thanks for all the help, Jeff.

My intention was to have an extremely convenient way to maintain a highly polished edge. If I had a system that would allow me to strop indefinitely without rounding the edge, I could simply strop a knife a few strokes before and/or after each use and I would never have to break out the stones.

Where can I find this viewgraph plastic?
 
Viewgraph is a brand name for overhead projector transparency stock. It is obsolete technology now that we have computer projectors. Anyway I would go to a big discount stationary store and look for "overhead projector transparency" sheets. While you are there you could look for various kinds of smooth flat plastic. You might find something intended for report covers, sheet protectors, notebook dividers, or file folders that would work as well. You want something smooth (so that your edge is smooth) and stiff (so that you protect your edge contour). You may also want to get some pads of paper to use as the support for your plastic. The pad will hold the paper in place.

Another thing you could try is to simply use a nice slick magazine as your strop. It is pretty smooth and stiff. I have also used computer photo-paper or plastic photo-paper as a stropping surface.

You may find that if you use nothing but stropping to maintain your edge you eventually get a weak edge with some flimsy burr at the apex. The problem is that your edge is flexible and bends away from your strop as you work. After a long period of stropping instead of matching the contour of your strop the apex of your edge will project out virtually straight like paper or foil. It will be weak and will flop over. The best way to keep this under control is to do a little edge-forwards honing (alternating sides left-right-left-right) at a significantly increased angle before every 10th stropping session. You even have to do this with straight razors. You can't maintain an extremely acute edge indefinitely solely by stropping.

Here's a link about deburring.
http://www.bladeforums.com/forums/showthread.php?t=355227
 
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