How long should I strop for?

L

Lennyo3034

Joined
Nov 27, 2012
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490
I use a strop with green compound to maintain my edges. However I get the feeling that I'm not stropping enough. I usually do around 10 passes alternating sides and then call it good. Takes about a minute. Would I be getting better results if I stropped for longer? I am applying minimal to no pressure when I do it.
 
Green compound as in CrO?
CrO is in the 0.5-0.3 micron range, it is for maintaining very fine edges such as straight razor edges. For knives if you are sharpening to 1k grit, stropping on 0.5 micron compound will not do much good as far as edge sharpness, the compound is meant to smooth not to sharpen. So if you want sharper edge you will need to go to 2-3k grit.
If you want to only strop and call it a day, you may need to consider lower grit compound, there are choices of diamond sprays which will work great on felt. I use 1 micron diamond spray and like it, but I am thinking of trying something coarser and see how it works.
Here is a link with very well priced compounds, I am not affiliated with those guys in any way other than I bought some spray from them a few years ago.
http://www.advancedabrasives.com/
 
IF the edge is fully apexed from the stones, AND if the steel is not too wear-resistant for green compound, it shouldn't take much time or strokes. S30V and similar high-vanadium steels usually won't respond as well to it; but 1095, CV and 420/440-series steels respond very well, for example. Used on the appropriate steels, you should get decent or even excellent results with green compound, no matter the coarseness/fineness of the edge finish (one of my favorite combinations is a ~320-grit edge on 420HC, stropped with green compound). The better the apex is, the less time/strokes it'll take. If you're not seeing any improvement in your edge after maybe 5 minutes' stropping, chances are some more work needs to be done on the stones, or the compound isn't aggressive enough for the steel. With the appropriate work done on the stones, it's possible to see some extra 'pop' in sharpness within 5-10 passes on a green strop. That's when you'll know you're doing everything right.


David
 
The steels in question are M390 and CPM-M4. I sharpen them on the edge pro, usually stopping at the 1000 grit stones, not polish tapes.

I can definitely notice an improvement after stropping for a minute or so, just wasn't sure if I'd see a better improvement if I were to strop for say...10 minutes.
 
Just stropped an M4 blade, about 10 passes per side. Blade whittled a thick hair(lets not discuss where it came from) but not the thinner hair from my head, which it could whittle when I originally sharpened it. Is that about all I can expect from stropping?
 
Lennyo3034 said:
The steels in question are M390 and CPM-M4. I sharpen them on the edge pro, usually stopping at the 1000 grit stones, not polish tapes.

I can definitely notice an improvement after stropping for a minute or so, just wasn't sure if I'd see a better improvement if I were to strop for say...10 minutes.
Click to expand...

Those steels are very high wear-resistance, with a lot of vanadium carbide content (tungsten carbide as well, in the M4). They're along the same lines as the S30V I mentioned; green compound could have a tough time abrading/shaping the carbides, therefore producing a fine edge. Diamond or a similar compound like CBN (cubic boron nitride) may be better for it.


David
 
I'm no expert, so someone tell me if I'm wrong on this.

I think strops, loaded with green, white, or black compound do very little polishing. Until you've gotten the edge very close to the grit rating of your compound, the polishing from the strop is negligible. I.E., it's not going to take the edge to a higher level of overall refinement or polish.

What a strop *IS* going to do, is remove any tiny remnants of burr stuck to the blade. I *think* it also micro polishes the grooves and landings in the existing scratch pattern. Doing some tests, I've noticed that just a very few strokes on a loaded strop will take a coarse edge (like from a DMT C) from paper tearing and hair catching, to paper slicing and hair shaving. 8 or 10 strokes on the strop didn't do anything to the scratch pattern on the edge. But it did remove burr remnants and apparently micro refines the cutting edge because you can see, feel, and hear the difference.

Brian.
 
In particular, SiC (black) and aluminum oxide (white) can be very aggressive polishing media, especially on simpler steels like 1095 and 420HC, etc. A distinction needs to be made, in that some of these compounds won't remove big, coarse teeth on very wear-resistant steels in a hurry, but they will still aggressively polish what is there. In other words, they can quickly refine the edges & tips of the teeth, as well as the valleys in between them. At the actual apex of the edge, that can make all the difference. SiC compound in particular can remove the teeth from a 320 or higher-grit edge pretty fast, if taken too far on a steel like 1095 or 420HC (this comes from my doing so on Case's 420HC stainless, as well as on CV and 1095). I use 600-grit SiC on balsa to remove heavy wires/burrs that otherwise won't be fazed by something like green compound or bare-leather stropping. And the SiC can quickly polish and over-polish these edges in doing so, if I take it too far.

So, in other words, if perfectly mirrored bevels are the goal, these compounds can't do it all by themselves; they need the proper prep ahead of time. On the other hand, if enhancing the cutting characteristics of the edge itself is the objective, they can quickly make all the difference. After all, it's the apex that makes it sharp or not; mirrored bevels won't help if that isn't done first. It's not so much about how much metal the compound removes as a whole, but the scale at which it can make the most significant difference.


David
 
In a very real sense, the strop has all the same limitations any other abrasive media will have, plus the issue of how much give the surface has. So, if the jump is too large to a finer abrasive, It won't have the desired effect but will still do some polishing. Under magnification, it is impressive how much of a difference a loaded strop can make. However, if the surface is conformable, the amount of pressure needed to remove appreciable amounts of steel will also make the surface deflect - it will remove even more metal with the higher pressure but with most of the removal along the apex, making the cutting edge more obtuse. On a coarse edge it might very well improve the apex and into some of the grind troughs, but imagine how the abrasive is getting there and what effect this is having on any adjacent high points - they cannot help but be smoothed out and will also be the first to round over with repeated stropping.

If you apply your compound to a piece of hardwood and cut it with a bit of oil, you can sharpen your edge. With a lower grit you can flatten, work out chips etc right down to about a 3-400 grit equivalent or lower, though beneath the 400 grit range you're better off with a stone or other fixed abrasive.

If using a deliberately conformable surface, the abrasive needs to be in line with the last stone you used (for best results). Prolonged stropping is not a good idea in this case, OPs observation of less than 10 passes a side is optimal. On a harder surface, many of the rules start to go by the board. On those harder steels, something more along the lines of AlumOx, SiC, diamond etc will be a better choice, but with the OPs current scenario I'd imagine hes getting a reasonable outcome.
 
There is more authoritative commentary here, so what follows is a FWIW.

On BF and other forums I've read several times that there is a proportional relationship to higher wear resistance steals to passes on a medium necessary to sharpen a blade. It has something to do with vanadium... Most of my experience is with O1, A2, 440c, and 3V. 3V always takes longer than O1, A2, and 440c.

I keep reading the term "refine and edge" when it comes to stropping. My take away has always been that the intention of stropping is to clean very fine metal particulate off of a sharpened blade and to polish it. Since the leather gives a bit, it "kind of" flexes into those small grooves left behind after sharpening.

Your blade might not be sharp enough coming off of the stones. 10 -20 passes on a strop is all it should take.
 
Depends on what your doing , if your using a good compound and a good progression than however much it takes to replace the scratches from your finishing stone. If your just jumping from a 1k or sandpaper or something to some green stuff then just a few strokes to remove the burr.

Bgentry hit the nail on the head.
 
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