How can stropping work?

H

huugh

Joined
Jul 16, 2005
Messages
1,772
How can (soft) leather without abrasive particles affect much harder tempered steel? What is the principle behind it?

If it shall be based on same principle as steeling, i.e. just applying pressure to align the last bit of edge - thin enough to be deformed in this manner - isn't the first time you cut something (i.e. you apply force on the edge to separate material being cut) all effect of stropping vanished?
 
huugh said:
How can (soft) leather without abrasive particles affect much harder tempered steel? What is the principle behind it?

If it shall be based on same principle as steeling, i.e. just applying pressure to align the last bit of edge - thin enough to be deformed in this manner - isn't the first time you cut something (i.e. you apply force on the edge to separate material being cut) all effect of stropping vanished?
Click to expand...

my understanding is the stropping actually polishes the blade as the compound+leather combo removes a very time bit of metal.

when you only use leather, you are doing two things: 1. polishing the edge adn 2. straightening any burrs that have formed during use or sharpening. When you add a compound, depending on the 'grit', you are actually removing a bit of the metal.

hope this helps,
brett
 
Last edited:
Stropping does all sorts of violent things, Huugh!

First, it does help align a deformed edge, as you suggest.

Second, if the strop has any adhesive properties (i.e. drag), it helps clean the edge of debris including residual bits of burr (in Korin's "The Chef's Edge," Chiharu Sugai strops on dampened newspaper at a 90 degree angle to remove burr remnants - and so can you!)

Third, most strops aren't just leather, they're also coated with all sorts of abrasive compounds ranging from the simplest sands to high-tech materials such as cubic boron nitride, boron carbide, and various types of natural and synthetic diamond. Even untreated leather often contains a little silica which is harder than most steels (though not the carbides on many modern steels).
 
Some time ago I read a description of the 'special' leather selected and offered by HandAmerican.

The claim was that natural silicates in the leather provided a mild abrasive action, with no further treatment required for finish-stropping.

thin enough to be deformed in this manner
Click to expand...

You seem to be referring to a 'wire-edge'. That's a failure of the most basic sharpening goal: To hone two edge bevels to intersect exactly.

Generally, the way to prevent wire-edges is to reform the final edge bevels to form an edge with a greater included angle.

The sharpest edges I've ever produced were stropped wire-edges. Such an edge will be an outstanding thread-cutter, but useless for normal EDC tasks, since it will collapse immediately in normal cutting tasks.
 
Last edited:
I use a lansky then finish off stropping with a piece of leather glued to a surplus piece of micarta that I have wiped over a block of the red polishing compound. It cleans the edge nicely giving a lasting edge.
 
Stropping with a leather strop, or with paper or cardboard or whatever, affects the hard steel the same way that cutting through those media does - just of the edge instead of on the edge itself.

When you strop, you are polishing the edge with the micro-abrasive effect.

When you are cutting, you are dulling the knife with the micro-abrasive effect.

Simple as that.
 
when a person sharpens well, and the two sides that make up an edge meet, there is extra metal hanging onto the edge, known as a wire edge or a burr. this is the same as when you grind a piece of metal on a grinder, the metal that comes off sometimes sticks to the piece and hangs off the edge. in the case of knives, as you polish the edge finer and finer with different abrasives (stones, belts, sandpaper, etc) you get a smaller and smaller burr.

the finest belt i have for my grinder is 9 micron. that leaves a very small burr, barely visible. it can be felt though. i strop it on .5 micron film to break off the burr and slightly polish the final edge. this also adds a bit of microbevel becuase i do it on flexible backing.

the point of stropping is to take off a burr, so that the edge won'y degrade too quickly when you are cutting. though even when stropping, you are leaving a micro-burr, it is so small that it won't have any measurable affect on edge durability. so you are taking off the burr, as opposed to steeling which just straightens the burr in line with the edge, leaving it there to degrade as media is being cut. this results in a sharper, longer lasting edge.
 
Grampa said:
Stropping with a leather strop, or with paper or cardboard or whatever, affects the hard steel the same way that cutting through those media does - just of the edge instead of on the edge itself.

When you strop, you are polishing the edge with the micro-abrasive effect.

When you are cutting, you are dulling the knife with the micro-abrasive effect.

Simple as that.
Click to expand...

+1
Best to the point explanation I've read yet.
 
Here's my understanding.. You are probably refining the very tip of the edge. It may be hardened steel, but at the edge, you are down to almost zero thickness. If cutting stuff can dull a knife, clearly soft materials can have an effect on the knife edge, good or bad.

But whats really happening is that you are polishing everything the strop touches, which should be the entire secondary bevel.. the part you just roughed up by sharpening. What's happening is that a polished edge moves the material you are cutting easier. It just feels sharper after stropping. Best analogy I can think of is that you can hammer a nail (smooth) into wood a lot easier than you can hammer a screw (rough) into wood.
 
The almighty strop is a mystical piece of the metallurgists' magically history. Passed down from millennias before you must first align the stroke of the blade with the North and South poles. Place your feet on the remaining cardinal direction of East and West. Preferably with your left on West and your right on East so that you are facing North.......best results are achieved during the August full moon.


To understand stropping you have to stop thinking of steel as "hard" material. Think of it as wood (it has a grain) and clay (it can be cut, ground off, or "smashed"). My understanding is that you can grind or cut steel with progressively finer grits or teeth. At the end of the day you'll still have a rough edge...then as a last step you can "smash" or push the very very thin tip of the edge into a finer, and smoother (or polished), point than you could ever cut or grind. This is what the leather or cardboard, or newspaper does. It takes all that work you did with stones and tops it off with a little push, or better put a "pull" on the material to remove the wire-edge and bring the material to a fine point.
 
Friction a peice of leather rubbed against a knife or vice versa creates friction
 
None of the responses seem to apply to convex edges. Isnt stropping the way to go when maintaining them?
 
I remove the burr before stropping. the reason I strop is that the 30K Shapton costs too darn much, I would go edge leading if there was something else that would allow it at sub micron abrasive size.
 
For a really sharp edge, after the leather and compound, I strop the blade on my jeans. I don't know how it works it just does.
 
You must log in or register to reply here.
Back
Top