Push cutting test

[matt321]

Exactly how do you test a blade's sharpness by push cutting newsprint? By measuring the distance along the paper edge from the grip to the blade? Is a little slice at the start allowed to get things going?

I can get a shaving edge routinely with my sharpmaker and the standard stones. I'm trying to progress beyond shaving arm hair, so I need a better measurement test.

 

[me2]

For a tougher test, try taking a hair from a brush and cutting it when held between your fingers. The fine rods from the sharpmaker will do this, as well as the medium if you're very careful and work mostly on the flats. I can sometimes get my knives to do this from the leather belt on the belt sander.

 

[Cliff Stamp]

Exactly how do you test a blade's sharpness by push cutting newsprint? By measuring the distance along the paper edge from the grip to the blade? Is a little slice at the start allowed to get things going?

You can hold the paper between your fingers and see how far from the point you are holding it you can cut it, the other is to fold the paper in a L shape and see how high of a fold you can cut with the just strength of the newsprint alone resisting the cut. Alvin Johnston was the first person I saw mention the second type.

Slicing, or using a draw is *MUCH* easier, it isn't even in the same class, I ran cardboard cutting trials recently and blunted some blades down to a few percent of optimal, they could still slice newsprint on a draw, a blade has to be *really* blunt to not do that. Any angle you use with respect to the paper also makes it easier.

Note you can do all of this with a sharp blade, it doesn't have to be polished, I recently took a Meuk (52100) with an edge from an x-coarse DMT hone and it could push cut newsprint about 1/2" from the point it was being held with no draw and all angles at 90 degrees, it would also shave (scratchy) and cut toilet paper on a slice but was problematic as the paper tended to stick to the micro-teeth.

-Cliff

 

[gud4u]

Slicing newsprint is one test that I always use.

Draw-slicing allows a simple test of the entire sweep of the edge, from heel to point. This is a good test for complete edge formation, and quickly identifies any area of the edge that is not fully sharpened.

Newsprint-slicing also gives two sensory feedback modes - pressure-to-slice and audibility. A moderately-sharp edge will sound harsher than the whispered hiss of a really sharp edge as the fibers are cleanly sliced. The newsprint vibrates, acting essentially as the fabric of your speakers as the fibers are either sliced or torn.

There is a serious potential for error in relying solely on newsprint-slicing - in that a sharpened wire-edge will not be detected. A few hard-pressure full-edge draw-slices on hardwood or plastic material is a good test for a wire-edge, collapsing or tearing off the wire-edge. Following this test, retest the edge with newsprint slicing to confirm a good sharp full edge.

Push-cutting newsprint is generally a test of edge refinement. Generally, a polished edge (fine-stoned or stropped) always excels at push-cutting. Some prefer a polished edge - some prefer a toothier edge for better draw-slicing performance.

Hope this helps!

 

[Broos]

I have grown to rely on Murray Carter's 3 finger test in addition to the old standards. Could be dangerous if you're not careful, but an easy way to identify a real sharp edge (or tell if you've rounded the edge by stropping).

 

[HoB]

the other is to fold the paper in a L shape and see how high of a fold you can cut with the just strength of the newsprint alone resisting the cut. Alvin Johnston was the first person I saw mention the second type.
-Cliff

That's the test that I am using for very sharp blades. Usually I get to cut about a 2" piece, but I find it also depends on the width of the paper aswell. So usually I cut a piece 2x2" in size and fold it. I got the idea when reading Perrin doing this with cigarette paper....too bad I don't smoke.

I don't like to use newspaper though, the Boston Globe is horribly inconsistent. There are sometimes almost woodchip-chunks in the paper that make this test a really pain. I usually use thin catalog paper. I always save old A.G. Russle catalogs for example. I also receive a chemisty publication which seems to be made from the same paper. It makes for good test cutting and is pretty much worthless otherwise. I find that paper a lot more consistent and smoother, but I don't know whether it is easier or harder to cut. Newspaper tears a lot more easily but it cuts not nearly as smoothly. I also find that I get more information from looking at the edges of the cut with the catalog paper. For a polished edge the edges are very, very smooth, while in newspaper there are pretty much always some fibers hanging out.

 

[Cliff Stamp]

Push-cutting newsprint is generally a test of edge refinement. Generally, a polished edge (fine-stoned or stropped) always excels at push-cutting. Some prefer a polished edge - some prefer a toothier edge for better draw-slicing performance.

You can push cut newsprint even with a very coarse edge, I have seen it with the x-coarse DMT finish. The ability improves with polish. Even very coarse edges, if well sharpened, should shave, push cut newsprint, etc. .

...it also depends on the width of the paper aswell.

The rigidity is dependent on the length, Alvin uses the full length of a phonebook. You have to have a consistent medium though, it doesn't matter really what it is, the exact numbers will change from one to another, but that doesn't really matter. You just calibrate them to what sharpness means from one to the other. It takes far less to push/slice photocopy paper for example compared to newsprint as the photocopy paper is mcny times more rigid.

-Cliff

 

[HoB]

It depends on the width of your "L" aswell. A narrower "L" has more rigidity than a wider "L". Only up to a point of course. Length of a phonebook page....damn...that must be one hell of a sharp knife!

 

[Cliff Stamp]

Yes, his knives are among the sharpest I have seen, and the one I have ne noted that the edges were only "decent". His edge angles are also really low, he considers 10 degrees per side for example to be obtuse and it only goes on the knives that are for scraping and such. The edge thickness is also extreme, full hollow grinds, blades that are 0.020" or so at 1/4" back from the edge.

-Cliff