Edge dulls easily after stropping

G

Gil P.

Joined
Jan 21, 2015
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116
I just got into stropping and I have a Habilis Nessmuk and an Ontario RAT 3. Usually I will finish sharpening the blades on a DMT extra fine and the edge stays for a long time. But since I started stropping, I have been having trouble with the edges staying sharp. I can cut a few pieces of wood and I will get noticeable edge rolling. I strop with black, white, then green compound. The edge does get very sharp after stropping but now it seems it makes the edge roll easily.

Could I be stropping too much? Sorry for the huge pictures.

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You might try first re-honing on the DMT EF, since you've said it stays sharp for a while after that; just to re-establish a good working edge. Then, try each of your strops (black, white, green) by itself, instead of in-sequence. See how your edge behaves after each one; it may be that the full sequence is over-polishing the edge, or one of the compounds may be too aggressive by itself and is over-polishing it. I've seen this with some black compound on leather, in particular; too many passes can over-polish an edge pretty fast, resulting in a rounded off and too-smooth apex.


David
 
Thanks David I will experiment with that.

I have noticed that after stropping, the edge feels smoother, but it push cuts better than the semi toothy edge I get off the DMT EF.
 
Gil P. said:
Thanks David I will experiment with that.

I have noticed that after stropping, the edge feels smoother, but it push cuts better than the semi toothy edge I get off the DMT EF.
Click to expand...

That's usually the expected result in refining to a more polished finish; as the 'teeth' from the diamond hone are reduced, the draw/slice-cutting may diminish a bit, but push-cutting should usually improve, assuming the apex still stays crisp & sharp, and doesn't get over-polished and rounded off.


David
 
What is probably happening, imho, is that you are rounding your very apex by using some type of soft strop media, which creates high pressures on the apex and bends it back and forth thereby weakening the metal. Clay Allison has documented just how much a leather type strop will round an edge when you aren't planning on it, and therefore has recommended that people lower their angle 2-3 dps when transitioning from a stone to a leather strop. You can also see the effect of bending metal back and forth causing it to become weak simply by taking a paperclip and bending it at a specific point 20-30 times until it breaks. This same thing can and will happen to the apex of your edge if you aren't careful.

So this is my suggestion... take your knife and "destress" the edge by cutting 3-4 passes, lightly, directly into a stone (preferrably a diamond plate). This will cut/shear off any damaged steel. Then sharpen on stones as normal getting a fresh, clean apex. Then check edge retention not stropping at all, then with light stropping (~5 pps), then heavy stropping at a slightly lowered angle. let us know =)
 
razor-edge-knives said:
What is probably happening, imho, is that you are rounding your very apex by using some type of soft strop media, which creates high pressures on the apex and bends it back and forth thereby weakening the metal. Clay Allison has documented just how much a leather type strop will round an edge when you aren't planning on it, and therefore has recommended that people lower their angle 2-3 dps when transitioning from a stone to a leather strop. You can also see the effect of bending metal back and forth causing it to become weak simply by taking a paperclip and bending it at a specific point 20-30 times until it breaks. This same thing can and will happen to the apex of your edge if you aren't careful.

So this is my suggestion... take your knife and "destress" the edge by cutting 3-4 passes, lightly, directly into a stone (preferrably a diamond plate). This will cut/shear off any damaged steel. Then sharpen on stones as normal getting a fresh, clean apex. Then check edge retention not stropping at all, then with light stropping (~5 pps), then heavy stropping at a slightly lowered angle. let us know =)
Click to expand...

I was playing with the compounds and found that the black compound seems to make the edge rounding on my RAT 3 happen faster than the others.

The edge keeps rounding on the same two spots on my RAT 3, it still happens on the rest of the edge, just not as quickly as those two spots. Coincidentally, I start stropping on those two spots on the blade. I strop the straight part of the blade and the curved part of the blade separately since I am still a beginner. I strop by placing the blade flat on the strop and, while moving it forward (towards the edge) I lift the blade until the edge just starts to catch on the strop, I use very light pressure, maintain the angle and move the blade backwards to strop the edge. When I lift my blade off the strop, I am sure not to roll over the edge.

I will take your advice Josh, and "destress" the edge to see if it helps.

The Nessmuk seems to have stopped exhibiting the strange behavior I described, it wont get as sharp the the RAT 3 though, maybe because the bevel is thicker on the Nessmuk.

I have been using two strops, one from The Knife Connection, and the other is a Stropman strop.

Ive got to run some errands now, ill try again in a few hours.
 
Could it be as simple as too much pressure is being applied when you are using the strop? I know that I have been guilty of this myself.
 
Just for the heck of it, try stropping on a single sheet of copy paper or similar (no gloss) wrapped around your stone/plate. Coming off the DMT EF you should be able to go right to the white compound, save the black for touchups between sharpenings and hold off on the green till you get a handle on what's happening.

The paper is a lot more forgiving in terms of rounding an edge due to pressure, and it manages a bit of additional tactile feedback compared to most leather strops.
 
Rounding off the apex with soft backed strops. Could even be forming a little burr that's rolling away under use.
 
I have good luck with using an instruction book from a piece of equipment I have. (about 10 pages) I fold it in half and pull my blades through it pinching with my thumb and forefinger to apply some pressure on the blade edge. (I am not cutting the paper but using it to strop the edge) The paper is fairly coarse paper and gives me good results by burnishing the finished edge. Since I am not applying pressure on the edge, there is no chance of rolling or rounding of the apex. It leaves black streaks on the paper, so I know it is burnishing the metal. I have a strop with compounds but no longer use them except with a stubborn edge.

Omar
 
Your edge angles appear to be extremely acute. If this is so, then perhaps the extra thinning provided by the strop is making the edge too weak.

Since you said you noticed rolling, im most inclined to think your edge is becoming too thin and weak from the stropping. If it was an apex rounding issue, the knife would come off the strops dull right away. A wire edge would come off sharp and dull instantly.

Use very very super light pressure, at a slightly flatter angle than you might think you need. Or the hard strop that was suggested. If all else fails, consider a less acute angle, if that seems to be the problem.

Good luck.
 
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I sheared off the edge and re sharpened my RAT 3 as Josh suggested. It seemed to hold an edge as well as it had done before. I then stropped it with the white compound on the Stropman strop; I also decreased my stropping angle. The edge got a bit sharper and is holding its edge.

Jamesh Bond,
What do you mean by my edge being too acute? Are you saying that I should decrease my sharpening angle? Wouldnt that make the bevel thinner? The Nessmuk's scandi bevel has a secondary bevel on it.

Heavy Handed,
I will try that method and see if it works better.
 
Gil.

My observation was only a guess based on the appearance of the pics. By acute, i mean low edge angle. Too thin. If this is correct then the remedy is to increase the angle on the stones a bit to create a slightly thicker edge. Just a few degrees. When stropping, go a hair lower than whatever you used on the stones to avoid rounding the apex.

Again, only a guess. The pics just appear that way. If i am wrong please disregard. Do you have an estimate of what angle you're using on those?
 
I'll try increasing the angle if I keep having the same issues as you suggest. I have no idea what angle im using. Do you think im expecting too much from the steel? I know the habilis is 1095, im not sure about the RAT 3 though, it also says Rowen on the other side. I bought it some years back before the two companies split, it is number 0776. Its either 1095 or D2.
 
Get a protractor and guesstimate the angle. I literally used to keep a protactor diagram on my phone to reference. Then i found an app that actually lets me hold the knife to my phone and tilt everything to line up the indicator. Pretty cool.

Those steels are both great when sharpened at the optimum angle. Good luck.
 
If you have a caliper or something that can measure to the thousandths then you can simply measure your edge and plug in the measurements here in the calculator, then it will tell you the angles =)
 
One thing bugging me here, in discussion of the edge being possibly too acute:

(quoting from the original post)
"...Usually I will finish sharpening the blades on a DMT extra fine and the edge stays for a long time. But since I started stropping, I have been having trouble with the edges staying sharp. I can cut a few pieces of wood and I will get noticeable edge rolling."
Click to expand...

If the edge is actually rolling, i.e. bending or folding to one side or the other, it should also exhibit this behavior after sharpening on the EF DMT or other hones/stones which set the angle of the edge. If it's actually too acute, the strop alone won't likely be doing that by itself, but the angle set by the hones/stones will. Presumably, the supporting geometry (edge angle) isn't being thinned enough by stropping alone to make it roll. If, on the other hand, by 'rolling', we're talking about the edge apex 'rounding' (losing it's crispness, but not folding or 'rolling'), then I could see how stropping might do that. Ordinarily, the strop is only going to refine the finish at the same edge angle set by the hones; if the apex angle is changing on the strop (of compressible leather), the apex angle would only likely become more obtuse, if only slightly, and not more acute; stropping on anything compressible won't thin the edge, in other words. This is due to the combined effect of the abrasive on the softish substrate (leather) wrapping around/over the apex and polishing the crispness out of it.

For the sake of clarity, I'm wondering which is actually happening: rolling (bending or folding) of the edge, or rounding (smoothing/dulling) of the apex?


David
 
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Good point. I thought of that too. My theory was that maybe the edge was just barely strong enough until the smoothness from the aggressive strops pushed it just over the edge. Just a long shot guess.

Could you clarify, Gil?
 
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