Push cutting paper

[gunmike1]

It's such a common thing that your request seems a bit silly. I have a digital Hi 8mm tape, but figuring out how to transfer that to my hard drive then up to the internet is a complete waste of my time in order to satisfy someone's curiousity. I'm far too busy to satisfy this request for such a mundane task. Many, many of us do this all the time to sharpen our edges. To infer that we're making it up, well, believe whatever you like...

Agreed. If I had a video camera I'd tape it, but I don't. With practice you can get an X coarse DMT finish to push cut newsprint, it just takes time and attention to detail, with a bit of OCD thrown in. I will see if I can borrow my in laws camera and make a video, but it isn't at the top of my list right now. When my knives stop pushcutting newsprint then I know they need a touch up, whereas a year and half ago I couldn't even get a knife to consistently push cut copier paper. Just practice, learn, and pay attention to detail and you too will be getting your edges to pushcut newsprint well away from the point of hold. Get most any new Spyderco and you will be able to pushcut newsprint at least 2" from the point of hold if you want a practical demonstration to satisfy your curiosity and give you something to shoot for in your sharpening sessions.

Mike

 

[Broos]

Dredging up an old thread, but the lack of push cutting vids stuck in my head for some reason. After doing it I prefer the paper roll cut, empty plastic bottle cut, or telephone book cut over this method, and they're funner, too. After doing it a number of time in differing ambient conditions, I think they play more of a role in this test than the other tests (though they undoubtedly play a role in them all). Try it with some paper that has sat out in the garage in the summer with 90% humidity sometime! You could cheat by getting the paper really really dry, I think.

So I finally took some short vids of it. I'll post them with the admission that I am inexperienced compared to many here. I used polished edges to get it done. I tried one knife that has a very thin and coarse edge, but it could not do it so I gave up. The little knife in the first video is my kydex cutting/scoring M2 knife made out of a saw blade (Thanks, Thom!). The edge has been surprisingly damage resistant in use.

 

[hardheart]

Try it with some paper that has sat out in the garage in the summer with 90% humidity sometime!

I've given up on phone book paper. Living near the Gulf coast does not help. It's 86 degrees indoors and 100% humidity right now.

 

[Nosetotail]

I have wondered if the way I adjust the paper edge with the knife edge till it kind of gets rigid is cheating. It seems to me that when I do this, I get a slight amout of slicing action. It certainly helps to see someone else perform a push cut to confirm the simplicity of it.

 

[Doberman_Dave]

Great vids Broos! Jimmy Fikes truly does some inspired/deranged cutting tests.

The test that sounds the best to me is to fold a cigarette paper in half, set it upright on a table and cut it in half (reportedly Fred Perrin at one of the NYC knife shows). It kind of eliminates most of the wiggle room for a push cut.

Cheers,
DD

 

[Broos]

\The test that sounds the best to me is to fold a cigarette paper in half, set it upright on a table and cut it in half (reportedly Fred Perrin at one of the NYC knife shows). It kind of eliminates most of the wiggle room for a push cut.

I would like to try that one. Those papers are pretty short, though - I probably would be cutting up the table as much as I would be cutting the cigarette paper!

 

[gud4u]

The straight 90-degree push-cut into standard newsprint is an easy test for any blade that's truly sharpened. If it won't pass this test, then the job isn't finished - the two opposing bevels simply don't meet to form a true edge in the area tested. This holds true whether the included angle is 20 degrees or 40 degrees. It also holds true whether the finished edge is CrO-stropped or 1200 grit.

For me, the most revealing newsprint-slicing test is a slow heel-to-tip draw cut through the newsprint, since it reveals the overall state of the edge along the full length of the edge:
- It's easy to 'feel' any differences in sharpness as resistance variations.
- It's easy to 'hear' any variations due to fibers torn vs. fibers sliced.
- It's easy to 'see' any variations as the cut swerves or step-jumps just a bit for duller or knicked areas.

Finally, a tip-cut by slicing with the tip to see how easily the tip penetrates the newsprint. It's very easy to sense whether the tip is finished or not with this test.

I find these two newsprint tests the best qualitative tests for overall blade sharpness.

My best slicer is a japanese kitchen knife with high hardness and <20 degree included bevel that I use as a cigar-cutter (converting one Churchill-length cigar to two shorter smokes). It push-cuts through the cigar without cracking the wrapper. Don't try this with a thick blade - this knife measures .065" thickness at the spine.

 

[Dog of War]

IMO the "right" way to pushcut newsprint or other paper is to use a method and technique that's consistent, repeatable, and allows you to measure relative sharpness.

In general the way I do this is to cut the paper to a specific size, hold it pinched between thumb (I believe using the thumbnail is best) and index finger with one edge horizontal, and try to pushcut straight into that horizontal edge keeping the blade perpendicular to the plane of the paper. The further away from the point of hold the blade is able to cut, the sharper the knife.

How far from point of hold a knife can cut will depend on many factors having nothing to do with the edge of the knife: e.g. quality and weight of the paper used, the paper's dimensions, how cleanly the edge of the paper has been trimmed beforehand and any weakness in the paper from handling/folding, etc. When I use newsprint for quantified tests of sharpness, I try to control these factors, which is pretty easy if you don't get too anal about it. When I'm comparing different blades through several rounds of cutting and am looking to compare relative sharpness, I have also found that supporting the lower portion of the paper makes for more consistent readings. But for absolute sharpness measurement -- more what I think of as "braggin' sharpness" -- I leave the paper free-hanging.

 

[Broos]

IMO the "right" way to pushcut newsprint or other paper is to use a method and technique that's consistent, repeatable, and allows you to measure relative sharpness.

I found that simply folding the paper and then cutting it with no hand hold at all was simpler & eliminated the variables that are introduced by holding the paper (how and where the paper is supported and the height of the paper being cut, both of which you mention).

You can then vary the sharpness level tested by varying the height of the fold. That was my thought process doing this, anyways...

Thanks for those two tests mentioned, Gud4u!

 

[Dog of War]

I found that simply folding the paper and then cutting it with no hand hold at all was simpler & eliminated the variables that are introduced by holding the paper (how and where the paper is supported and the height of the paper being cut, both of which you mention).

You can then vary the sharpness level tested by varying the height of the fold. That was my thought process doing this, anyways...

Thanks, Broos, that's really very clever IMO; I'll have to try it out! If you were doing rounds of testing, I can see where it would be very convenient to have several pieces of paper already set up with folds at different heights. Could really speed things up.

 

[knivesandguns]

Well my knives must be dull.
My rainbow leek could push cut line paper fine, but could not do the same with the newspaper.

 

[gunmike1]

I found that simply folding the paper and then cutting it with no hand hold at all was simpler & eliminated the variables that are introduced by holding the paper (how and where the paper is supported and the height of the paper being cut, both of which you mention).

You can then vary the sharpness level tested by varying the height of the fold. That was my thought process doing this, anyways...

Thanks for those two tests mentioned, Gud4u!

Those were very nice videos and this method of testing you came up with seems like a real nice way to test push cutting sharpness. A quick couple cuts at different fold heights showed me quantifying how big the fold is has a major effect on whether or not a knife could make the pushcut, and it takes a lot of the hand held variables out of the equation. I'll have to mess around with this the next time I get a chance to play around with sharpness testing.

Mike

 

[MVF]

I have yet to get any of my knives to consistently do this, but I have BRKT NorthStar that when I got it would easily pushcut thin paper. The interesting thing to me is that the edge was pretty "toothy". That knife was a slicing/cutting monster! Equalling that kind of performance is my sharpening goal.

 

[Broos]

Thanks, Broos, that's really very clever IMO; I'll have to try it out! If you were doing rounds of testing, I can see where it would be very convenient to have several pieces of paper already set up with folds at different heights. Could really speed things up.

I'll admit I still mainly do this test by holding the paper like you explained, though. It's pretty tough to get easier than just grabbing some paper and cutting it. And I'll often do it the way gud4u explained, also (to get that feel of the entire edge). Either way can give you a good indication of sharpness.

I do not know whether these are as good as some of the other testing I've seen here (I can find issues with all of them!), but it is an easy way to gauge for yourself how sharp a knife is (or how well they push cut). It wouldn't surprise me if humidity affected paper more than the thread test (?), because it sure can affect how easy it is to cut paper.

I agree that to have a toothy edge that can push cut (almost) as well as a polished edge is a good goal to aspire to.