Difficulty Learning To Use A Strop

C

CutterBoi

Joined
Nov 19, 2022
Messages
28
I'm having difficulty learning to use a strop.
I can put an edge on most of my knives using diamond stones and a very fine ceramic stone. However, when I attempt to use a strop loaded with compound, I invariable dull the edge of the knife rather than making it sharper.

Example:
K55K knife, C75 carbon steel blade (supposedly similar to 1075)
15 degree bevel, tiny 20 degree secondary bevel
DMT Dia-Sharp diamond fine (25 micron) > Dia-Sharp extra fine (9 micron) > Norton Ascent ceramic ultra fine (~J8000)
The blade is sharp enough to very easily cut hair on my arm, and to cleanly push-cut copy paper width-wise.

Stropping with any of the following combinations only dulls the edge:
TechDiamondTools 3 micron diamond paste 50% concentration, on a suede strop
Sharpal green compound, purportedly ~1 micron chromium oxide, on a suede strop
Norton 1 micron diamond paste 50% concentration, on a suede strop
Kent Supplies 0.5 micron diamond paste 15% concentration, on a smooth strop

I'm clearly doing it wrong.

I am trying the minimal-pressure method. Stropping with the same angle I used on stones dulls the blade, even on a smooth strop.
I've read that I should find the right angle by slowly, carefully running the blade edge-first down the strop, starting with the blade laying flat, raising the spine just until the edge starts to catch / bite, then slightly reducing the angle. I've tried this but I'm unsure how much bite to target. Am I looking for the point where I just start to feel the slightest bit of strop texture being transmitted through the knife edge? Or the point where the edge begins to grab the texture? Or the point where the edge begins to grab the solid leather?

More importantly, what does it feel like when I'm stropping at the proper angle? Should the knife feel like it is smoothly sliding / gliding across the strop? Or should I just barely feel texture through the knife blade, the faint vibrations as the edge lightly caresses the surface texture of the strop? Or should I solidly feel the texture of the strop as the blade moves across it?

Thanks.
 
I like to strop flatter than might be intuitive. Think "bevel" rather than edge and let the strop sort of sneak up toward the edge.

If you strop on jeans when you're wearing them, you'll see you don't need to be particularly precise because of the give (of the material and your supporting flesh).

I don't want to feel the edge dragging on the strop media...whether fabric, leather, or basswood.
 
On a substrate like suede, I'd minimize or even eliminate the use of compound at all. Any soft substrate like suede or other soft leather or one which will tend to compress under the edge, or wrap around the apex of the edge, will tend to round over the edge if any abrasive polishing compound is used, UNLESS you're very careful and also more experienced in the touch for using it. And it's more tricky trying to maintain flush bevel contact when stropping very narrow secondary bevels or microbevels on a soft substrate with compound. As with all things in sharpening, everything can work better with more experience. As you gain experience and develop a touch you know works well, then you can circle back and retry some of the things that're giving you trouble now.

Try the compounds on a clean piece of paper over a hard backing like hardwood, plate glass or laid atop a sharpening stone. The single thickness of paper over the hard backing will mimimize how much the paper compresses, and therefore minimize the risk of rounding or dulling the apex. Alternatively, try the compound on bare wood and skip the paper. Again, this additionally minimizes the opportunity for rounding of the apex and will leave the edge much crisper.

Save the suede for bare stropping only, WITHOUT compound. In that capacity, it's serving more to clean up loose, weakened remnants of burrs without being too abrasive against the apex. And for the C75 carbon steel, I'd keep the choice of the compound simple too - like using the green compound on the firm/hard-backed substrate. Diamond compounds really aren't necessary for such a simple steel and can be overkill as well. If the stropping method or technique is tending to round over the apex, diamond will simply do it much faster.
 
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Thanks all for your information and recommendations. I think I've made a break-through!

I spent many hours stropping on smooth leather and suede leather, with and without compounds of various types, at all sorts of different angles, examining the edge under a newly-acquired 30x binocular microscope to see what effects my attempts were having. The microscope showed that the edge just wouldn't improve beyond a certain fineness no matter what I did. While no burrs were visible, the black apex was covered with bright spots, which I interpret as being flat, reflective surfaces where none should be.

Stropping dulled the edge every time. The edge eventually reached a point where I was unable to return it useful sharpness with my Norton ultra-fine ceramic stone. I tried to redo the micro-bevel but this only made things worse. I finally reset the main bevel, working through grits from coarse all the way to ultra fine, eliminating the micro-bevel in the process. This finally made the knife sharp again. More importantly, stropping is now improving the edge. I'm relieved that stropping isn't a skill totally beyond my physical ability.

I haven't yet tried alternatives to leather for stropping but this is something I intend to try. I'm more comfortable and consistent with stones than leather strops. Stones give me better angle feedback than leather does, so my hope is that something harder and smoother than leather, maybe MDF, will be an improvement. I'll continue practicing on leather until I get the materials for this.

Next question:
Approximately how many strokes on a strop doped with chromium oxide compound should be required to bring a carbon steel blade to maximum sharpness? I know there are a lot of factors, but I'm hoping for something general like "anything more than 300 strokes per side is a waste of time for any type and hardness of carbon steel". I can have a lot of patience and focus, but that sometimes leads to a longer learning curve as I think "maybe I've just not gone far enough" and consequently waste time.


Thanks again!
 
CutterBoi said:
Approximately how many strokes on a strop doped with chromium oxide compound should be required to bring a carbon steel blade to maximum sharpness? I know there are a lot of factors, but I'm hoping for something general like "anything more than 300 strokes per side is a waste of time for any type and hardness of carbon steel".
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Goodness no, anywhere near that amount will have a negative affect on your edge, especially on a soft substrate.

Start with the bare minimum, 5 or 10 very light strokes per side. Test the edge and take it from there.
 
Regarding the number of strokes question -

As pointed out by 777 Edge above, you really want to minimize the number of passes. Stropping is all about the last, final refinement to the edge. It should produce a noticeable improvement in sharpness within the first 2 - 5 featherlight passes per side on the strop. Shouldn't take more than a minute of your time. If you're going to 300, or even to 30 strokes and not seeing any improvement, that's a definitive clue the edge wasn't ready for stropping in the first place. First, you need to do as much on the stone as you can to thin and reduce the burr before taking it to the strop. If the burr hasn't been thinned out enough and the apex not refined enough, stropping won't help at all and will instead further round off, overpolish and blunt the edge.

Additionally, if you do notice improvement in those first few passes, it's generally good practice not to take it further - especially with compound. Overstropping a very sharp and very fine edge will always diminish the result on any soft substrate like leather used with compound. Knowing when the edge is ready for stropping, and also knowing when to STOP stropping, are equally important.
 
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I do my best to eliminate burrs before I move to strops. I'm using the lightest stropping strokes I can achieve while maintaining consistent contact with the strop.
So, based on what you're posting, if I ever reach "tree-topping" sharpness, it will be with only a few strokes on a strop, right? I don't want to have my blades consistently sharpened to that degree, but this is what I'm targeting for learning / training purposes.

Here's an image I managed to capture through my 30x microscope of the blade of C75 steel I'm practicing on. The blade is sharp enough to very easily shave hair on my arm, but is not "tree-topping" sharp, and is not getting sharper. The number and size of shiny spots is not reducing. (There is no burr visible through the microscope.)
C75-Level7.png

Am I at the limit of apex fineness that can be achieved on this blade? Or should I be able to get this knife sharper if I can get a more refined apex on stones before hitting the strop? The last stone I use before hitting the strop is a Norton Ascent ultra fine ceramic stone.

I recently acquired a new Spyderco Endela in K390. The blade wasn't quite as sharp as I expected, so I gave the blade a few strokes on the ceramic stone, and now it's the sharpest knife I have. The apex of that knife's edge, viewed under 30x, is significantly smoother (very few shiny spots, apex is mostly visible only as a dark line) than what's shown in in the above image. And I've not stropped the knife.

I have a Gerber Freeman Skinner fixed blade knife in 440A that I acquired in the early 2000s. The knife's edge was also most recently touched up on the ceramic stone and, like the Spyderco knife, has an edge with far fewer reflective spots than what we see above. The bade on this knife was profiled and sharpened using a WorkSharp Ken Onion machine on the 25 degree setting. Interestingly, this same machine has always been unable to make the K55K knife (or any of my other cheap carbon steel knives for that matter) anywhere near as sharp, though this may be attributable to difficulty in maintaining angle when sharpening lower-height knives.
 
You are playing with a lot of variables at once, including the final edge structure and hardness. Some of this is going to just have to come via feel, and experience. There is a range of "toothy" edge that will grab hairs and cut them off, then as it becomes more polished, pushes them aside, then finally hits a point where the "tooth" of the hair is catching the blade instead, and then cutting again. Also, as you fatigue, it can become very easy to put more force than is needed, this causes the final edge to have a higher final angle than what you were wanting, or to have odd rolls and drag the edge more than intended. It sounds like you are on the right track, just let things develop over time, and you will start to find the connections. Again, try to isolate variables, they might not seem to matter, but you don't know that for sure yet.
 
Just a quick one - are you 'pushing' or 'pulling' the knife on the strop?
 
I haven't found that stropping really does much to improve an edge. My grandfather used a strop to touch up his straight razor, but the old razors were quite a bit softer, around 45 RHC from what I've read. Strops even with some sort of chromium oxide or diamond compound don't seem to achieve much with today's much harder steels.
 
Alberta Ed said:
I haven't found that stropping really does much to improve an edge. My grandfather used a strop to touch up his straight razor, but the old razors were quite a bit softer, around 45 RHC from what I've read. Strops even with some sort of chromium oxide or diamond compound don't seem to achieve much with today's much harder steels.
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They are brilliant bits of kit if you just need to retouch an edge. After gutting, skinning and butchering a deer recently, all I needed was a quick strop of my knife to bring the edge back. No aggressive steeling or stones needed.
 
CutterBoi said:
C75-Level7.png
Click to expand...
omg this is a 30x image and from here already we can tell that the apex isn't sharp. i posted 100x images on the forum somewhere and even at the higher magnification the apex should look like a clean straight smooth fine line.

i wouldn't strop this rough apex but spend more time on the stones to refine it.
 
Alberta Ed said:
I haven't found that stropping really does much to improve an edge. My grandfather used a strop to touch up his straight razor, but the old razors were quite a bit softer, around 45 RHC from what I've read. Strops even with some sort of chromium oxide or diamond compound don't seem to achieve much with today's much harder steels.
Click to expand...
I would take those numbers with a grain of salt, as the surface hardening difference between the spine and edge on a straight is a far higher ratio than it is on a knife. Most straights would be too delicate to be tested after production anyway. Overall though it really depends on the steel, hardness is less of a factor than abrasion resistance, and those are not directly linked. I'd guess that the biggest extreme would be a very hard 1095 blade vs a pretty "soft" 3v blade, I would expect that even if the 1095 blade was harder Rc-wise, the 3v would still be more abrasion resistant.
 
Ruari said:
Just a quick one - are you 'pushing' or 'pulling' the knife on the strop?
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Edge trailing. As for how I'm moving the knife, I don't know how to classify. The strop is in front of me so, when looking at things in relation to my body, I'm pushing for one side of the knife and pulling for the other. As for my grip on the knife, I try to keep that light and "neutral" so as to minimize the angle shifts caused by my natural, random twitches, shudders, and variations in movement as I move the knife along the strop. So the focus of my grip tends to be on a point that lies very close along the blade's natural twist-axis. Clear as mud, I think.

I suspect there's something wrong with this knife blade. I'm switching from the K55K in C75 to a 2nd-hand Kershaw Leek in 14C28N for learning purposes. I've re-ground the bevels to correct the bad sharpening attempts of the prior owner and reduce the edge's angle to 30 degrees inclusive. The edge already looks far better under then microscope than that of the K55K, and I haven't even finished using the DMT fine stone. I plan to do a little more work on fine, then extra fine > extra extra fine > Norton ultra fine ceramic, where I'll stay until I'm 100% sure things are as good as I can possibly get them on stones. I'm moving very slowly and carefully to give myself the best platform for success in stropping.
 
I have confirmed that there's no point in excessive stropping on leather with abrasive compound. Doing this does in fact round off the apex, even with very light strokes gliding on flats of the bevel.

I have discovered that a line of closely-spaced, tiny bright spots on the apex when viewed under 30x may indicate a micro-burr, even if you see no overhange. This will be accompanied by a significant reduction in sharpness. With the K55K in C75 carbon steel, three-to-five consecutive light strokes on the side over which the burr overhangs will clean it up and bring back the sharpness.

Readers should be aware of a few things before they purchase a cheap digital microscope:
* The camera assembly has little or no focus adjustment ability. Focus is controlled primarily by distance between this assembly and the target. The stand / base bearing the camera assembly on the majority of cheap digital microscopes reportedly have horrific issues with fine adjustment. This compromises the utility of such devices.
* The camera assembly usually has to be placed very close to the target. This may impede your ability to easily examine your knife under magnification from various angles.
* The claimed "magnification" on these units can be very misleading. If you take a close-up picture of your skin with the camera on a cheap phone, then get that picture printed out to billboard size, how much have you magnified your skin? 1" of skin may be printed to cover 14' of billboard space, which could be claimed to be 168x magnification. But how useful is that magnification? Not very. Stand right in front of the billboard and you'll discover that the dots making up the picture are quite large, so you won't get a whole lot of useful detail. These cheap digital microscopes operate similarly. They have a simple lens set that focuses light from a small point onto a larger (but still small) image sensor. The more "pixels" in the sensor, the greater the captured detail. The finer the focal point, the greater the captured detail. A very close focal point restricts depth of view. The lens set on these cheap digital microscopes does not come anywhere near 1000x magnification, and much of the claimed magnification is actually enlargement; the tiny dots picked up by the image sensor are displayed as big dots on the viewing screen, whether that be your phone, a computer monitor, or a small display affixed to the microscope's stand / base.
I don't have any hands-on experience with these cheap digital microscopes but, based on my experiences with a 30x binocular microscope, I can say that the focus issues littering reviews of cheap 1000x digital microscopes will likely hide some of the fine flaws in the apex I was able to clearly see with just a 30x optical binocular microscope. I'm not saying these cheap digital microscopes are useless; many people appear to be happy with their performance. Just take the claimed magnification with a grain of salt.

I'm still working toward that hair-popping, tree-topping edge, slowly inching forward. I will get there.
 
It looks to me like wood is indeed a far better stropping substrate than leather for use with compounds. Home Depot paint stirring sticks work. Basswood works. But I like Beech the best so far, because sanding it up to 2000-grit sandpaper gives it a smooth, burnished surface. Sliding a knife across this wood feels significantly better to me than the other woods I've tried so far.

Getting closer to my goal of tree-topping sharpness. This little "gem" is almost there. Say hello to the sharpest knife presently in my home!
Cheap-Bait-Knife.jpg


Ain't she a beauty? :D
I think I paid $2.00 for her when new, and even that was probably too much. She's stained and scratched up. Lighting gives a false impression of bevel shaping, but the bevels are still quite bad. I hacked away some of the blade's heel to make the knife easier to sharpen on my DMT stones, which have small margins along the long edges where there is no abrasive. I did some crappy re-profiling to significantly reduce bevel angle to, I'm guessing, somewhere between 10 and 15 degrees per side. Need more practice on that, my hands kept trying to do a ~20 degree angle. This was a quick-and-dirty, destructive experiment to determine whether a soft steel would limit the sharpness I could attain. Looks like the answer is "no". Or, put another way: It's not the blade, it's me.
 
Many, many hours and knives later, I've finally brought a knife to tree-topping sharpness.
Knife: Spyderco Grasshopper
Steel: 12C27 Stainless
Bevel angle: Whatever came stock on the knife. Quite low, whatever it is.
Equipment used: DMT DiaSharp coarse, DMT DiaSharp fine, no-name fine ceramic stone, Norton Ascent ultra-fine ceramic stone, Sharpal green compound on unknown wood (Home Depot paint stirring stick), 0.5 micron diamond compound on basswood, 0.25 micron diamond compound on beech.

Target sharpness was reached on the Norton Ascent ultra-fine ceramic stone. Subsequent honing compounds further improved the edge but weren't needed to meet my goal. I've not yet used a leather strop on this knife. I plan to try a few strokes on plain leather to see if the edge improves further, and will abandon use of leather strops entirely if I see no improvement.

Spyderco-Grasshopper.jpg


Major observations:
* Maintaining a consistent angle is extremely important
* My fingers feel burrs far better than my eyes can see them. I need glasses...
* Burrs can be difficult to see even under magnification
* Burrs can exist even when I can't see or feel them
* I should not move past the DMT fine stone, or any other hone higher up the grit sequence, until I feel no burr, see no burr, and have done a good number of alternating strokes to ensure that whatever burr remains is as small as possible.
* Ultimate edge sharpness is highly dependent upon the level of perfection I achieve on the DMT fine stone.
* Hones and strops are very limited in the degree to which they can improve a poor edge left by a lower grit.
* My best results are obtained when I don't try to rip off a burr (run the edge across some wood, or run the edge down the stone at an elevated angle) until the very end of the sharpening process, if at all.
* The repetitive motions of sharpening can lead to dangerous complacency. Pay attention! I cut my wrist while bringing a knife closer and turning it edge-up for close inspection. I was very lucky I didn't seriously injure myself. The scar left behind serves as a reminder to be mindful every time I see it.
 
Congratulations on your journey. Well done.
 
Congrats on the improvement! I'll suggest picking up the inexpensive Carson Microbrite Plus 60-120x pocket microscope, it's only $15 online and surprisingly works really well. I just leave at 60x as that's plenty of magnification to see the apex, and it's easier to keep in focus at the lower power. I can see the smallest of micro-burr's with that and it really helped me in cleaning up my edges.

Also, the Edge-on-Up BESS sharpness tester has helped me improve the quality of my edges. I've found that tester is very good a detecting any amount of burr or rounding of the apex. You need to have a very clean, precise apex to get a reading of 100 or below. Yes the tester can be "cheated" into low scores, but I have no interest in that. I use the machine to help me understand the level of sharpness I'm getting. Many times I think I'm finished with a knife so I take a BESS reading only to discover the edge needs more work.
 
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