Stropping without rounding the edge

If you are rounding the edge, you are doing one of a few things wrong.

Pressure..........You don't need or want pressure when stropping on leather. The leather (most leather) has a bit or even more give.

For light knives like pocket knives. No pressure. The weight of the knife and no more is necessary.

For bigger knives, like my heavy choppers, I will actually keep them lifted. If you don't, you might just be "wrapping the edge" and dulling it.


Or, you may be sweeping the edge. As a lot of people strop, at the end of the their stroke, there is a natural tendency to lift the spine as they finish. Almost like they are giving a little "flourish" or finishing lift. This will just dull the edge.



Be very "methodical" through the stroke about keeping the angle the same, or even going shallower.

I tend, toward the end of the stroke to back off the angle just a touch. It does no harm, and just polishes a tiny bit higher on the shoulder.



You can strop "hard" if you have a very firm backing. Like wood, or glass, or particle board etc.


I have a bit softer strop, so I take more care.


You can also strop at a much shallower angle and use more pressure. I have had success doing this with a leather strop, where the force is is causing the leather to try and "wrap" the edge, but because I am at a much much shallower angle, it is "wrapping" the edge at the correct angle.

I have done this with great success with a heavy chopper (10 inch .32 thick spine). It was tiring to lift the weight of the knife ( I spent a long time re profiling the edge, and then polishing it). So I went much shallower on the angle, and let the heavy weight of the knife rest on the strop. (Some one else had told me that trick, so I was not reinventing the wheel).
 
If you are meaning stropping in the nominal sense, that is running the blade over a grit impregnated underground such as leather or linen, but even the palm of your hand could be considered a strop with the ever present grime and dirt as the grit, then you will necessarily round over the edge every time whether you perceive it by unaided observation or not. On his website, The Japan Blade, Alex will lay it all out very understandably for any and all interested readers.

E.DB.
 
I use plain leather, no compound. I strop often throughout my sharpening, usually between stones. If I am using a more coarse grit, I use the rough side of the leather. As I finish, I use the smooth side, with lighter pressure. This is done on a bench. It seems to work for me, YMMV
 
SirSharpSauce said:
I've abstained from stropping lately because it only results in rounded edges.

How do you guys do it?!
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The term "stropping" can mean an awful lot of possible methods.

If you're talking about using a piece of leather loaded up with abrasives, then there's a real good sticky at the top of the page. The leather is conformable and pretty much uniform, allows the abrasive to sink into the surface rather than sink into the steel and produce a more uniform edge when viewed from the side. Unless great care is taken to prevent it, the pressure will spike along the apex as the leather returns to its previous volume after the edge passes over.

Even with light pressure this is liable to happen unless the surface area of the blade is large, spreading the pressure out more. A lighter touch is helpful too, but then it will require more passes across the surface to see an effect. Even if the edge isn't sinking into the leather, there is a tendency over time for the edge to round over with repeated stropping due to human error. Convex, Scandi, and straight edge blades seem to do best over time, these edges have a lot of surface contact - reduces spot pressure and increases feel for where the cutting edge is relative to the leather. On a V bevel you can roll the shoulder into the leather and use this to absorb some of the pressure, align the cutting bevel a little better to the line the leather takes as it expands - more pressure on the shoulder, less on the apex.

Even then, many people use a coarse and fine strop, this gives more bite to the leather with the coarse grit for refreshing the edge, then refine it a bit with the smaller abrasive. When using a leather strop, you should do as much possible work on your fixed abrasive (hard stones etc) as you can to reduce the chances of it going wrong.

Either way, the edge will become more uniform and polished as all the abrasives are hitting the edge with much more uniform pressure. Even with a relatively coarse grit the edge will feel smoother when cutting due to the greater uniformity along its profile and a smoothing of the grind troughs as they intersect with the apex.

To reduce the likelihood of rounding the edge, use a harder backing. Either compress the leather when its damp (there are instructions in the stropping sticky authored by Stitchawl), switch to MDF or balsa, wrap a sheet of paper around a combination stone, or check out the Washboard link in my signature - I made specifically to counteract both the smoothing and rounding effect from most stropping operations, but retain the ease of use and burr free removal of steel.

This at 1000x (1600 with digital boost), there is no rounding of the cutting edge, the edge stays three finger sticky - very catchy yet capable of treetopping hair or even whittling a hair:

after stropping with compound on two sheets of paper

1000_CMP_Calibrated_146u_zpsa2fa8796.jpg


And after stropping on one sheet of plain paper

1000_CMP_PP_Calibrated146u_zps7383f13c.jpg


If you don't care to invest in a Washboard, at least try using a sheet of paper wrapped around your stone - apply compound to that. The coarse side works better. In general, stropping is a great way to tune-up an edge, finish an edge off, maintain an edge with specific cutting qualities all with the least possible amount of steel removed - just have to figure out what combination of grit, surface, and backing to use, and how much pressure you can get away with.
 
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Tell us how you strop (duration, etc.) and what the edge is like before you start stropping (do you do test cuts before you strop? do you deburr?). Tell us what you use (which strop, which compound, etc.).
 
I've gotten away from leather and prefer balsa wood. It cheap, makes the compound used work faster and has very little chance of rounding your edge unless your drastically change the angle.
 
My mantra for stropping is along these lines:

  • Lighter pressure is always best.
  • Firmer substrates are almost always best (wood/balsa especially; or very thin & firm leather, cardboard or paper on hard backing).
  • Most edge refinement should be done on the stones, before stropping.
  • Stropping shouldn't take more than a couple minutes' time, and ideally shouldn't need more than 10 passes per side, on an edge.

It also helps greatly to get acquainted with how different compounds & substrates work with a given steel. Varying combinations of both factors can make a huge difference, either good or bad. Some compounds are too aggressive for some steels, even at very fine grit, and can quickly over-polish and round off edges. This is why it's beneficial to try many different combinations over a span of time, and see what works the best, with the least amount of time (passes) invested. Stropping almost always degrades sharpness when taken too long or too far.


David
 
Again, thank you all for your help. With the balsa wood strops, I've found an expensive set from the American Strop Company. Would I be able to use any piece of flat balsa wood instead? And what compound/paste do you guys recommend?

Also, will a properly stropped edge still have cutting aggression? After the stones, my edges bite pretty well, but after stropping they tend to slide across the fingernail with little to no aggression. Is this because of my improper technique? How is it supposed to feel when touched?
 
SirSharpSauce said:
Again, thank you all for your help. With the balsa wood strops, I've found an expensive set from the American Strop Company. Would I be able to use any piece of flat balsa wood instead? And what compound/paste do you guys recommend?

Also, will a properly stropped edge still have cutting aggression? After the stones, my edges bite pretty well, but after stropping they tend to slide across the fingernail with little to no aggression. Is this because of my improper technique? How is it supposed to feel when touched?
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Any piece of smooth wood will do. Doesn't have to be dead-flat, but a smooth and uniform surface is best. You can find balsa at hobby supply stores, and it's usually conveniently cut to widths ideal for stropping (2" - 4" is common, in thicknesses around 1/4", give or take). They also often carry basswood cut in similar fashion, and it should work well also.

The 'best' compound will depend a lot on what steels(?) you're sharpening. Green compound is great on simple carbon steels like 1095, CV, etc. Also works very well with simpler stainless, like 420/440-series, AUS-8, 8Cr, etc. So-called 'black' and 'white' stick-type compounds are very versatile with most steels. Diamond compound is ideal for very wear-resistant steels like S30V, etc.

Most of the 'aggression' you'll want in an edge should come from the final grit of stone you use. If you like a toothier edge, finish on a relatively coarse stone. Any stropping done afterwards should just basically clean up burrs & wire edges, and perhaps polish the 'teeth' a little bit. Too much stropping with more aggressive compounds (black, white & diamond) on a softer or less wear-resistant steel can polish a lot of 'bite' out of a toothy edge. So, as always, 'less is more' when stropping. If you find yourself needing to strop for more than 5 minutes on any blade, odds are you're overdoing it, and the sharpness usually suffers as a result.

A really crisp and somewhat aggressive edge should 'bite' a little bit, if feeling with your fingertips. A well-executed and highly-polished, crisply-apexed edge can deceive you; be careful. It can slice almost painlessly in the skin. On a fingernail, a crisp edge should immediately catch in the nail (toothy or not), and not slide off the tip of the nail, when just laying the weight of the blade on the fingernail (as if getting ready to shave a thin sliver of nail off).


David
 
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