Mixed results stropping - advice?

D

Dog of War

Joined
Sep 4, 2004
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I've been stropping knives for years, but am a little embarrassed to admit with varying degrees of success. With compound like CrO I've never been satisfied with results I get on smooth leather..... on rough leather it's much better, particularly if the blade has a pretty low edge angle.

I've read a bunch of stropping guides and posts on forums. Maybe I'm not holding the angle steady? If not, how do you do it? (I can freehand sharpen fine so I don't think it's a motor control deal.) HandAmerican's suggestion of raising the spine till the edge just bites the leather then backing off slightly doesn't work even using blade-weight only pressure and being careful not to lift the spine at the end of the stroke.... I either get no improvement or round the edge. And if I do see some good result it's only sections of the blade. BTW I can do tools like chisels, I assume because of the large flat edge.

Any suggestions or tricks? Or should I just stick with rough leather and low edge angles? Could it be leather that's too soft, or too hard, or too much compound?
 
I'm no stropping expert, but I'll contribute what little I know about what works for me.

I use the HandAmerican method you described, although I admit sometimes I put a bit more pressure than just blade weight - but it seems to work fine.

Now, you mention "too much compound", which may be part of the issue. You'll want the leather to be in there as much as the compound. I can still see plenty of leather showing through the CrO, but if I wipe my finger on it a little green comes off on it. That should be just about right.

Another thing is, I get the knife good and sharp on stones and then only do a few strokes on the strop. I've heard that it's too easy to go to screaming sharp, then keep stropping and begin to undo what you've achieved.

And finally, maybe you're doing everything right and you just have higher standards for what constitutes "sharp" than I do. :)
 
Thanks. Thinking it's time I order a strop and compound from HandAmerican.... having the right leather and compound, designed to work as a system, sounds like a smart thing to do if I'm going to try relearning it right.

One other question, I finish sharpen almost all my knives with a very minimal microbevel, and depending on the steel, the "difference" between the microbevel and primary edge angle can be pretty large - say, like a 40 degree included micro on a knife profiled to 20-25 degrees included. I wonder if this is a factor, having only this very small final edge offering very little bearing surface when stropping? Maybe that steep little shoulder between edge bevel and the relief portion explains why rough strops are working for me, but not smooth leather, the rough stuff being able to give and flex over the shoulder and just "lick" the final edge?

Thanks again. I doubt it's my high sharpness standards, Torz; you're the one who's got things working, and I'm still trying to figure it out. :)
 
Sounds like you're 'rounding' the blade edge.

Because of the elastic nature of a leather strop, you've got to carefully control both pressure and the incident angle between strop and blade.

Use a lower incident angle on the strop than you do on the stone. This will tend to form a mini-convex secondary bevel - rather than simply rounding the edge.

Using an abrasive on the strop, mirror-polishing will be visible quickly. Rocking the blade under strong light will reveal the mirrored-zone where the blade is contacting the strop. Start at a very low incident angle and check the mirrored zone to see where the strop is contacting the blade. You want to kind of 'sneak up' on the incident angle until you're forming a mini-convex secondary bevel that just reaches the edge (sharpening) - instead of actually rounding (dulling) the edge.

Hope this helps!
 
Dog of War said:
I finish sharpen almost all my knives with a very minimal microbevel, and depending on the steel, the "difference" between the microbevel and primary edge angle can be pretty large - say, like a 40 degree included micro on a knife profiled to 20-25 degrees included. I wonder if this is a factor, having only this very small final edge offering very little bearing surface when stropping? Maybe that steep little shoulder between edge bevel and the relief portion explains why rough strops are working for me, but not smooth leather, the rough stuff being able to give and flex over the shoulder and just "lick" the final edge.
Click to expand...

You have to adjust the stropping angle just like using a stone. Leather is more forgiving to slop, but it isn't limitless. I run the same profiles, often more exteme like 2-3 with a 15/20 micro, usually it is 8-12 primary and then 20 micro. The green buffing compound works very well for a few passes, the sharpness degrades beyond a few passes and you lose massive amount of aggression for little gain in push cutting sharpness.

-Cliff
 
OK, I seem to be getting somewhere now. And all three of your posts have been very helpful.

Freshly sharpened knife, strop ready ..... deciding to work really slowly and carefully, I angled the knife moving edge forward just until it bit into the leather. Then doing all I could to hold the angle (motor skills are not what I thought, holding the angle pulling right-left is tough for me using blade weight only) I slowly, lightly stropped edge trailing. Two passes per side, working each section and patiently working the belly made a noticeable improvement on an already shaving sharp edge.

After doing the first side, I looked for the mirrored zone and sure enough, I see exactly what you mean, gud4u. Let's you spot areas that didn't get hit, too-- good trick!

And just like you said, Cliff, a couple more passes turned out to be too much of a good thing. Results were very good with only like a total of 6-8" of stropping travel, doubling that ends up dulling the edge.

Appreciate the help, guys, I think I better understand the principles of what's happening when stropping. It all makes sense, too, when I consider how effective I know rough side stropping can be, just the lightest of pressure on the edge is all you want.
 
Hm, technically you are lapping and when lapping the lap should be softer than the thing you are lapping (the grit embeds itself in the softer surface and scratches the harder surface) Which is why things like sticking a sheet of mylar or acetate on a piece of glass etc. have been suggested (grit embeds in the plastic). Copper clad circuit board has also been suggested (and ought to work pretty good, though I'm not sure how optically flat circiut board material is and copper compounds aren't exactly non-toxic). Soft cast iron is the favored material for making machinist's laps as it is softer than steel, cheap enough to be made into thick flat plates, and can be surface scraped if needed (scrape off a thin layer of the lap itself to get rid of the embedded grit if you need to change the grit you normally use, escpecially if going to a finer grit).

The advantage to hard leather is that it IS flexible, because knife blades are generally not flat (grab your favorite kitchen knife, or non-collectable outdoor knife, and lay the side flat, lengthwise, on a new 8000-10000 grit stone and give it some short push-pull strokes (in the heel to tip, tip to heel direction) and look at the blade... you'll see little polished spots because the blade is actually curved in places, wavy and full of dips and bumps (some caused by the forging, some by holding the side against the buffing wheel a bit longer in one spot than another). Your edge may look straight, but it is also wavy to some extent. Leather is flexible enough to conform to the waves along the length of the edge (a good thing), but if you use too much pressure, it will also flex parallel to the width of the blade, possibly enough to round the edge if your angle is too steep (that is why they tell you to find the angle where it bites then back off some and use light strokes. If you're rounding your edge, that means you didn't back off far enough and/or using too much pressure).

It may not work for you, but what works for me is on knives with a wide secondary bevel (the one that actually forms the edge) is to pretend that instead of trying to strop the edge, that I'm polishing the corner right where the secondary bevel meets the primary bevel. On knives with a very thin secondary bevel, I just lay the primary bevel flat on the strop as if I was trying to polish the side of the blade. It doesn't seem like it would do anything to the edge, since it is not touching the leather when I get all set to start a stroke, but somehow, quite by magic, it does (I'm thinking maybe little grit laden fibers spring up after the blade passes and whip at the edge sort of like a bunch of microscopic flap wheels).
 
I think what I've learned here explains a lot, not just smooth leather stropping but what's happening when you strop on rough leather, or polish an edge with a buffer, even.

Having used rough strops for a good while I know you can dull an edge with one of these too. It just takes longer because it's the "fuzz" on the leather that's doing the work and giving you the very, very light pressure needed. Plus I'd assume it's more forgiving than smooth leather.

Something else .... I sometimes deliberately over-strop, and then go back and reapply the microbevel with the Sharpmaker fine rods, ever so lightly. This produces some of the most consistent and fine edges I can achieve (of course I learned this from the many times I've dulled an edge stropping.)

To me edge consistency is very important and tells me the whole job was done right. I understand better now how a little bit of very light stropping actually can refine an edge. Outside of that, stropping, except like that with a hollow ground straight razor laid down completely on its spine to guarantee consistency, isn't nearly as precise and consistent as what you can achieve on more solid media, particularly if using some mechanical means to control the angle (jig, v-rods, etc.)

I would think with very fine solid abrasive and precise angle control, you could exceed the sharpness you can get by stropping. I know a couple guys who use "scary sharp" for tools in their wood shops and they don't strop. And if you consider razor blades, which as I understand are neither honed nor stropped .... well there obviously are ways to get an edge as sharp or sharper than stropping.

After all this I have to laugh because I can't say that I really think stropping makes a better working edge for 99% of the stuff I cut with a knife. It's just the challenge and having the skill, because someday I might need it for something, you know? :) I'll keep working at it, if I come up with any breakthroughs will let you know.

Thanks for all the help everyone.
 
Dog of War said:
Something else .... I sometimes deliberately over-strop, and then go back and reapply the microbevel with the Sharpmaker fine rods, ever so lightly. This produces some of the most consistent and fine edges I can achieve (of course I learned this from the many times I've dulled an edge stropping.)
Click to expand...
I have experienced the same thing ( by mistake ).
In my case, with the EdgePro, I go back to the grit size I used just before I stropped. Just a few swipes each side to re form the edge but not too many.
The trick seems to be to know when to stop, just before you re form the burr. But the edge produced this way is very ,very sharp.
 
First of all, the knife has to be either shaving sharp or very close to shaving sharp for stropping to even have an effect. If an edge won't take hair off your arm first, even with considerable effort, it's a lost cause.

I actually strop at a slightly steeper (higher) angle than I sharpened and I use a very flat, smooth loaded strop, not a rough one.

Also, try lying the strop on the soft arm of the sofa and working while you're in front of the TV, rather than using it hanging.

.
 
When you compare the hardness of chromium oxide (the green buffing compound) with the hardness of steel alloys you should be able to enhance your edge through the cutting action of the compound while you are stropping. On straight carbon steel and some of the softer stainless (like 12C27) this has worked for me. On the fancier stainless grades it doesn't seem like I get much advantage over plain leather. Maybe that is from stropping too hard or too long.

On the other hand when I use submicron diamond grit I can substantially improve my edge. I use a somewhat complient backing when I strop, usually a pad of writing paper. I cover it with a somewhat stiff material, usually photo paper or plastic view graph slide material. The combination is complient over a scale of millimeters, but is relatively smooth and straight on a scale below a millimeter. Half micron and quarter micron diamond dust does a more uniform job of cutting carbides than I get with chromium oxide. It allows me to get a finer edge without rounding. I use very light pressure and try and match my primary edge angle rather than my micro-bevel. I allow for the strop complience to take the strop around to the micro-bevel.

I often go back and put a ceramic micro-bevel on my finished edge. That can get me a lower micro-bevel angle than a strop wants to produce. It also gives a micro finish that slices well.
 
This is great information, guys. I figured there was more to this than what I understood, but it's becoming obvious that slight changes in abrasive, leather (or whatever holds or backs the abrasive) stropping angle and pressure can change results drastically.

It would be interesting to see under magnification what the surface of a piece of leather we think of as being "smooth" and "hard" looks like when a blade edge comes in contact. I suspect there's a surprising amount of give, maybe even microfibers like suggested, depending on the leather.

I'm also interested that I'm not the only one who often adds a final microbevel after stropping .... I've always wondered if it wasn't just because my stropping lacks skill that I'm satisfied with an edge finished up this way. I mean, you never really know how sharp that edge is when somebody else is telling you about it in a book or post on a forum..... though I've read a ton of your posts, Jeff, figure you're "the man" when it comes to sharpening, so if it's good enough for you, I'm sticking with it.

BTW I don't remember this "Toolshed" forum when I started coming here, only the last few months it seems. It's the first thing I visit when I log on to BFC now.
 
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