Help with edge aggression!

S

SirSharpSauce

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Aug 1, 2013
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Would someone please educate me as to why my knives lack the edge aggression to cut objects other than newsprint or the like?

Although my knives are mirror polished by stropping compound and can pushcut/slice newsprint and shave hair, the end result does not have the aggressiveness of a coarsely sharpened knife and cannot bite into what I am cutting. I can literally run it across my fingers without it cutting into me.

Does it have something to do with my stropping? What am I doing wrong?
 
Over agressive stropping can round over and edge as well as polish out the microserrations that even a fine sharpmaker ceramic will leave. Go back to the rods and reform the burr, then remove as much of it as possible using light strokes on the rods, and finish with 2 strokes per side on the strop, you should get most of the bite back. A good coarse edge will still have more aggressiveness but the fine ceramic stones are quite capable of putting an edge on that will bite into the pads of your fingers.
 
I run my PM2 with a 34 degree polished bevel and a 40 degree medium grit microbevel. The MB adds some bite to the blade, but it can still pushcut most things.
 
SirSharpSauce said:
Would someone please educate me as to why my knives lack the edge aggression to cut objects other than newsprint or the like?

Although my knives are mirror polished by stropping compound and can pushcut/slice newsprint and shave hair, the end result does not have the aggressiveness of a coarsely sharpened knife and cannot bite into what I am cutting. I can literally run it across my fingers without it cutting into me.

Does it have something to do with my stropping? What am I doing wrong?
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The preceding responses all have good points, especially the possibility of rounding. There is also the amount of variation along the cutting edge. Once an edge has been polished to the level where it appears unified, it has fewer features to catch on some materials and begin a cut. Depending on what you're testing against, there are substantial performance gains/losses relative to how the edge has been prepared, and with what abrasives.

Next time you're sharpening an edge with a full progression, take the time to deburr cleanly at every stage, stop and do some testing of several materials. Better yet do three edges, one coarse, one medium, and one fine. This way you can do your own head to head testing.

Last thought, examine your fingerpads a day or two after doing a three finger test where they didn't feel sticky. Sometimes you're cutting across the fingerprint without catching. After a day or two and with the skin dry, small cuts in the outer surface will be visible.

HH
 
HeavyHanded said:
Last thought, examine your fingerpads a day or two after doing a three finger test where they didn't feel sticky. Sometimes you're cutting across the fingerprint without catching. After a day or two and with the skin dry, small cuts in the outer surface will be visible.

HH
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this has been my experience with the crispiest mirror polished edges, the 3finger tests doesnt work with those. at least with my calused fingers. i often feel nothing until i reach enough confidence to cut myself to blood.

for the op, there are several ways to obtain a mirror polish, imho a charged strop is not the best one, a charged strop should be the last step for edge cleaning, it's not good for completely replacing a scratch pattern with a finer one. keep minimal passes on the strop and if you want a more refined scratch pattern buy the uf rods. the edge will be crisper if the desired polish is obtained from a hard substrate and stropping kept minimal to clean the edge.
 
There is also the scratch pattern to think about. This was my problem when i first started stropping. I though i was rounding the edge cause i could still puch cut but lost all slicing ability. But the way i was stropping (heel to tip/edge trailing) was causing the scratch pattern to change orientation. I found out that it still would slice, but in a push slice instead of the usual pull slice. I had to learn to strop tip to heel which still feels weird to me.
 
My two Spyderco "Militaries" of CPM M-4 and S90V are my "Braggin Rights" knives.:D

I sharpen to 30K Shapton, then strop to .25 micron.

My final test is to take the knife into the lavatory and "dry shave" with it. (Not a whole face shave, just a couple of swipes.)

If it passes this test, the edge will feel fairly smooth to the touch.

I've never had a problem cutting anything with them.
 
In my experience the more polished the hardrr it is to touch my edge.

I know many using sharpmakers get fantastic looking mirror edges but very blunt, I dont get how that happens.

My mirror edges are almost untouchable and smooth. I dislike toothy.

I strop on a 8000 stone VERY lightly and it pops hair, thick asian hair.
 
HeavyHanded said:
The preceding responses all have good points, especially the possibility of rounding. There is also the amount of variation along the cutting edge. Once an edge has been polished to the level where it appears unified, it has fewer features to catch on some materials and begin a cut. Depending on what you're testing against, there are substantial performance gains/losses relative to how the edge has been prepared, and with what abrasives.

Next time you're sharpening an edge with a full progression, take the time to deburr cleanly at every stage, stop and do some testing of several materials. Better yet do three edges, one coarse, one medium, and one fine. This way you can do your own head to head testing.

Last thought, examine your fingerpads a day or two after doing a three finger test where they didn't feel sticky. Sometimes you're cutting across the fingerprint without catching. After a day or two and with the skin dry, small cuts in the outer surface will be visible.

HH
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SO very true. I'm sometimes amazed at how ugly my fingertips look, the day AFTER I've spent time sharpening, stropping, testing, feeling the edges on my knives. They really get carved up, but I often don't notice how much until hours later, at least. I often notice it first, when rubbing an eyebrow or my cheek to scratch an itch or whatever, and my fingertips feel like files on my face. My immediate reaction is, "Where in heck did THAT come from??" Then I notice all those little parallel cuts on my finger, that I just KNEW weren't there before. :D

As mentioned, either rounding or over-polishing, or an edge angle that's a bit wide can all impact how aggressive the 'bite' will be, when initiating a cut. With tougher materials especially, like hard plastic or cardboard, a wide/obtuse edge angle (V-bevel) can really get in the way. If the apex is very clean & pure, just convexing the shoulders of a somewhat wide V-bevel can make an improvement. But, thinning the grind and edge angle will make the bigger difference, and can forgive a lot of variation in edge coarseness/polish otherwise.


David
 
Same thing happens with me, I mirror polish my knife, resulting in smooth, quick slicing of paper, but when it comes to biting down on things, it just slides across with no incision. If you are looking to have an all around knife to do daily urban tasks, I would recommend starting coarse then move on to 1000 grit paper, after that you may do some medium stropping. Heck, even the jeans you're wearing can do a considerable job stropping, it works just fine for me. I think mirror polishing my edc knife is a waste of time, I will only do it if I need the knife for a specific, precision demanding job. Takes practice and some patience if you want a proper mirror edge, rounding it off is not that hard to do by accident.
 
None, I just use a Norton India stone and remove the burr or refine the edge on that. DM
 
I just use green compound on my jeans.

There's no way your finger will slide down a blade without getting cut if it's really sharp, mirrored or not.
 
Since I took these micrographs for the "Washboard vs CS Recon" thread, thought I'd paste them over here. Pretty sure most folks understand to some extent the correlation between edge aggressiveness and grit rating. Not sure how many people have had a closer look at edges from various grit levels - might make it a little easier to visualize just how these edges interact with a material when cutting, why some edges last longer when used for different tasks, and why some edges are just a poor choice for certain jobs.



All pics at 640x, the ripple effect visible in some of the scratch patterns is camera-induced.

First one is off 320 grit sandpaper, test knife is a smaller Voyager - Aus8 flat grind. I did nothing to it coming off the sandpaper except to do the best job I could in terms of burr removal and a wipe on my pant leg. This edge can just shave some arm hair - cannot crossgrain pushcut newspaper. Can crossgrain drawcut very fine curls from the newsprint.
WB_640_320_zpsd3faadab.jpg


Same edge after stropping on paper - noticeable improvement in cutting. It can now just crosscut newsprint but very noisy and hitching as it goes. Drawcutting is a dream - edge is very catchy yet can shave a bit more arm hair.
WB_640_320_Paper_zpsfb4d5cb6.jpg


On to the 600 grit,straight off the sandpaper - cutting even better than the 320 grit with paper stropping, at least in terms of fine cutting - will now crosscut paper noisily but confidently, still plenty of bite. A real good kitchen utility edge. Can shave arm hair a little better, almost clean.
wb_640_600_zps0ce3da89.jpg


And after stropping with paper, about 30 passes with moderate pressure. A very nice jump up in cutting ability - now crosscutting paper quietly yet still plenty of 'catch' to the edge. Shaving arm hair cleanly, still three finger sticky.

wb_640_600_Paper_zps05778188.jpg


On to the compound. Another jump up in fine cutting yet still very three finger sticky. Now very close to my comfortable upper limit for EDU. Again, easily crosscutting paper with a whisper and cutting a circle from same paper. Didn't test it, but likely capable of treetopping some leg hair. At this point, probably not capable of cutting rope etc as well as either the 320 grit edge or the 600, and certainly not for as many cuts. A large jump in chopping though - consider how much less friction is being generated compared to the 320 grit edge when pressed into a material. Consider how much more friction is being generated by the 320 grit edge when drawn, and how those larger edge features will tear into a material when drawn across.

WB_640_Compound_zps4cdd6780.jpg


And after stropping with paper, again about 30 passes. Now feeling very sharp, cutting across my finger pads when I do a three finger test. Still feeling a bit of "drag" as it does so, I can make out the surface cuts - they'll be more visible tomorrow. Still some surface variation along the apex, but nothing compared to the 320 and 600 grit edges. Estimated at a 4k JWS. With even more polish those edge features will disappear at this magnification and the mechanics of how the edge cuts will continue to shift favoring pressure cutting and chopping.

WB_640_Compound_Paper_zps8a1b60ca.jpg


Here's a last one, not from this series but decided to add it anyway - same magnification. This is off a Spyderco EF stone and stropped on Flexcut Gold followed by plain leather. Both this edge and the preceding one could whittle hair. This edge now has almost zero edge variation - little advantage when cutting to draw with it, almost a straight pushcutter/chopper. Micron scale in upper left is the approx width of a single red blood cell 7.7u (actually a blood cell is a little larger). Edge is no longer three finger sticky - with light pressure it slides across the fingerprints until enough pressure is applied that it will cut.
CAT_640_Scale.jpg
 
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I never got much edge improvement when stropping on plain paper (perhaps some after 200 passes)until I applied slurry to it. Then I noticed a step up in improvement when stropping on leather with the same slurry applied. I think the pores in the leather hold the slurry better. If you don't let the blade get closer to dull then stropping is an effective edge maintenance and saves steel on your blade. Thanks for posting the series of photos and all the effort sharpening that went in to it. Different stone binders will leave a different looking and cutting edge than coming off sand paper. Plus the difference of edge leading or edge trailing strokes. Then I've noticed an edge is capable of push cutting sisal rope coming off a 320 grit Norton India stone. DM
 
Wow, thanks for the photos HH! you def. have technique down if you can do that all by hand! what kind of microscope/metallograph you using?

I think those photos demonstrate exactly what happens in a toothy vs polished edge.
 
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