Cardboard Stropping

O

old4570

Banned By Request
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Jul 28, 2010
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Ok , a little history first !
Kizer Domin Mini
N690 55/50HRC ( 55HRC file bites / 50HRC file skates )
Previously on the rope this knife rolled @ 150 slices 4 times and with a wet stone grinder edge ( 80 grit ) it did a 200 roll ..
I chose this knife for it's low performance on the rope !

Previously the edge was 22 degrees .. This time I went 20 degrees .
Starting with a 180 grit diamond ( guided knife sharpener ) to make a new edge , then 600 grit diamond to clean it up . From here I went to 1500 grit oxide stone to clean some more .
Then I went to my 5000 grit stone till the edge had some shine to it .

Cardboard strop :
30 Can Pepsi Box cut up with a piece saved to strop on .
Why ? Well !
A) I have always maintained that you can strop on almost anything and get a sharp knife
B) Some people use cardboard with compound
C) Cardboard in itself is abrasive
D) & I have always wanted to try it

The edge turned out real nice .............
What surprised the heck out of me was the 550 Fail ... Only a 350 slice increase from the knives previous best ! ( of 200 )
The N690 is soft , so a 550 fail is just mind blowing ( still feels like fantasy ) .
I mean , all I wanted to do was sharpen a knife with cardboard ( strop ) . I was not expecting a serious gain .
This is only the very first time I have tried this ( stropping with cardboard ) .

So for now the rope slice is over , the knife remains un touched .
I will video the cardboard strop back and see what happens , then see what result we can get on the rope slice after the strop back .
But still , what a shocker of a result !
 
I'd postulate a big part of the improvement probably came just in narrowing the edge angle a little bit, from 22° down to 20° (I'm assuming these are per-side numbers).

It's known, and has been verified by CATRA & others, that narrowing the blade thickness and the edge geometry makes a significant improvement in working edge retention and is probably the greatest influence on it, for any one given steel. This works well even in softer steels down to mid-high 50s HRC. The whole premise behind the better edge retention is based on the useful cutting ability lasting longer, simply due to the narrower cross-section of the blade & edge, even after the apex dulls a bit. The steel behind the edge, being thinner, will still allow an edge with a moderately dull apex to cut well, or well enough to keep working. It also means the pressure exerted to cut something needn't be as high as with a thicker edge, which reduces the damaging force exerted into the edge itself. Edges at 40° (20°/side) or wider will not cut very well without a very crisp apex. Once the apex dulls, cutting performance drops dramatically in that range.

Stropping on cardboard & other simple materials can work too, to maintain edge sharpness in softer, more ductile steels which will usually be more in need of edge alignment, as opposed to repairing edges dulled by abrasion. And some heavy cardboards can be dirty enough (in other words, abrasive enough) to perhaps do some actual sharpening by abrasion. I've noticed this with simple carbon steels in particular - those having less wear resistance than stainless steels. And narrower, thinner edges are inherently easier to realign & resharpen as well. It sort of goes against the old conventional wisdom that a thicker, more obtuse edge will last longer. It will, in the sense that it'll retain its shape better. But that sort of thick, wide geometry never really cuts as well to begin with, as does something a bit narrower.

I've been liking all of my edges narrowed down to the 25° - 30° inclusive range - they work especially well for cardboard. I use simple stainless for that, the large majority of the time, like 420HC from Buck (high 50s HRC) or Case (mid/high 50s HRC) or basic carbon steels like 1095 or CV. I don't ever use anything with an edge wider than that. And when they're in that range, they'll sharpen more quickly and also strop more responsively on simple materials.
 
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Yes , I expected something from going to 20 degrees from 22 Per Side ...
But no way in heck did I expect a 350 slice gain .. So maybe ? I just hit the G spot by accident ?
I have sharpened another knife exactly ( as much as I can ) the same way and maintained the edge angle ( Ruike 801 - review posted ) .
Again this was suppose to be about using cardboard as a strop , not gaining anything from it .
+ I have two other knives ( also tested / reviewed ) that have been sharpened and carboard stropped ..

The goal was to dull the edge and cardboard strop it back ! That was the idea ...
 

Video of the strop back on Cardboard.

Ok , a few post strop observations :
I think the cardboard has a short shelf life :
A) The more you strop , the more you polish the cardboard
B) The more you polish the cardboard , the less abrasive it is
C) The less abrasive the cardboard is , the less effective it is
D) I'm going to need more cardboard .....

The knife just did not want to get sharper , and that could be due to the cardboard being less abrasive the more I used it !
And that was my only piece of cardboard !
I have a box full of SOLO cans , which should empty out by the week end !
Thankfully I already sharpened and cardboard stropped some knives ..
But , looks like the Strop Back testing is going to be on hold for some fresh cardboard .
I got the Kizer reasonably sharp , but not as sharp as when I did the rope test .. Due to the expiration date on the cardboard ( short strop life ) .
It's all good fun and I have only just started .. So where will this go ?
 
Cant be bothered editing video for a 150 slice fail ..
Strop back on cardboard was 150 F ( F for fail )
That's a rather huge loss from 550 ..
Though , the edge was no where near as sharp as for that 550 result ..
That cardboard had lost it's Mojo !
I have leather + compound stropped the edge back , but still a little less sharp than for the 550 result .
Was that 550 just a delusion ? Hmmmmm .
Still , this knife used to be a 150/200F knife .... So there is that . ( Back to normal )
 
There's too many variables you can't eliminate. I've notice huge gains when I get rid of an edge that was tempered or burnt on a belt sharpener at the factory. Sometimes 3-5 sharpenings after getting the knife. In order to be more scientific you should eliminate variables. I'd do the same 20 degree edge regular strop vs cardboard strop. If you're just trying to compare the strop don't change anything but the strop. I have noticed some of the people I see do sharpness testing try several edges several times to see if their results are a freak of nature or legit. It's a lot of work. I think you're all crazy but I watch sharpness testing videos. Guess it takes one to know one.
 
The Kizer has been sharpened a lot Cos it wont hold an edge well ..
it's been on the wet stone grinder several times as well on the guided knife sharpener .
Testing has only just begun .. ( Early days )

Again , the original test was to see if cardboard can strop back an edge .. The 550 was seriously unexpected ..
The reason I chose this knife was for the low rope time .. Anyways .. I will keep testing this knife ..
The Ruike 801 was sharpened the same way .. With no change in bevel angle .. If anything , the 550 result has messed up my testing .
I have leather stropped + compound re sharpened the knife .. Lets see what happens .
 

Video has the cardboard strop back result and leather + compound cut test .
Anyways , on leather and compound the result was a 250F ( fail ) .
Im just about out of rope , then a new rope has to be started . What to do ?
Cos the rope is a variable .. Do I just go straight to the Ruike ? For a comparison against the first cut test .. ( Sharpened as close to the same as I could ) .

Remembering that that cardboard was well polished and no longer as abrasive .. So the knife would only get so sharp . ( It's a dogs breakfast as far as testing goes )
I might have to start again with a good supply of cardboard and new rope ..
 

Ok....

I used a ceramic rod , then cut rope .. 200 Fail
Then did a 1500 / 5000 grit re-sharpening job that resulted in a 450 fail
Then did a pure cardboard strop back .. Which returned a 300 fail
 
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