My Push-Cutting Goal

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rummels

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Mar 15, 2013
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I am trying to understand what changes I would have to make to my sharpening technique to be able to go from easily slicing newspaper to being able to push cut newspaper. Note that, when I use the term "push cut" I mean touching the edge of the knife to the edge of the newspaper with the knife at a 90 degree angle to the edge of the paper, and then just pushing the knife straight down, without even the slightest slicing motion.

When touching up my Henckels kitchen knives I have been setting the angle of the stones at 18.5 degrees. I use edge-trailing strokes and start with an 800 grit diamond stone and finish with a 1000 grit diamond stone. After each grit I do 2-3 very light edge-leading strokes at the same angle that I used while sharpening. At the end I strop with light to moderate pressure at a low angle with clean denim that has been glued to a very flat piece of oak.

Given that my knives do get reasonably sharp, I believe I understand the basics (burr formation, uniform scratch patterns, checking the angles at which the stones contact the blade, etc).

So I am wondering if there is some part of the process of sharpening that I am excluding or not executing properly that would get me to the point of being able to push cut newspaper. Is it the keenness of the edge as defined on the Science of Sharp website?

https://scienceofsharp.com/2014/08/18/definitions-of-sharp-and-keen/

If so, would stropping with a stropping compound create the keenness necessary to accomplish my goal? Would using 6 micron and/or 9 micron lapping films help?

Thanks

rummels
 
rummels said:
Given that my knives do get reasonably sharp, I believe I understand the basics (burr formation, uniform scratch patterns, checking the angles at which the stones contact the blade, etc).
Click to expand...
Hi,

Its time to forget everything you know
;):D


Which stones are you using exactly?
Can you push cut magazine paper? or printer paper?
What happens if you strop on left side only, can you feel a burr afterwards on the right side?
 
My apologies. I originally drafted my post with the intention of posting it only on the Wicked Edge forum, and didn't reference the fact that I using a Wicked Edge WE130 sharpener. I obviously should have mentioned this in my post here on the BladeForums.
rummels
 
CasePeanut thank you for the video. Unfortunately, because of how the video was shot, I can't tell whether or not B bgentry is push cutting in a way that meets the strict definition that I am following. But in many of the cuts he is making, it is clear that he is starting his cuts with a slicing motion. Sometimes it is very slight, but I have found that even the slightest slicing motion will make it easier to start the cut, and not meet the definition of a push cut that I am trying to follow.

A clearer definition of the push cut that I am trying to accomplish would be to use one spot on the edge, straight down, no back and forth slicing.
Thanks again
rummels
 
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My video that casepeanut posted wasn't intended (by me) to be a push cutting illustration. It was an illustration of tooth versus polished edges.

You are clearly looking for a highly polished edge that will initiate a cut at the slightest touch to the edge of paper. A typical "1000 grit" diamond plate is not all that fine, due to the shape of the diamonds, which will create deep angular scratches in the edge. The edge will be good, but it won't be super polished, which is what you are after.

I've had good luck with stones in the 3 micron range. My 5k water stone produces a very polished (visually) edge that does some nice tricks in paper. My Spyderco UF 8x2 stone produces one of the most polished edges I've made. Blades finished with this stone have a fine edge, which cuts into paper so easily it made a friend of mine laugh when he tried it. My progressions with the Spyderco UF was generally DMT C, DMT EF (9 micron), and then the Spyderco UF. While the UF did not completely erase the scratch pattern from the previous plate, it certainly polished it up very, very noticeably and improved the push cutting a lot.

I personally find this type of edge to be not that useful. I like it on the razor blades I shave my face with. It's fun to do tricks with and to show off. But it doesn't seem to be a super practical edge. At least not for ME and how I use a blade for daily tasks.

I did make a video that you might want to see, which briefly explores paper cutting and angles and things.


Finally, you might consider a more objective measure for sharpness. I bought the BESS tester and learned some things right away from it. Since it produces a number for sharpness, it's repeatable, comparable, and objective. Nothing like cutting paper or shaving hair. A score of 105 is sharper than 125, which is sharper than 150. All 3 are VERY sharp. 105 is just the sharpest of the three. You don't NEED the BESS tester. But depending upon your approach and your personality, you might really enjoy having it.

Good luck with your goal. Sharpening can be really fun.

Brian.
 
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A push cut is a slicing motion. You’re simply slicing into the material, not towards you. The blade geometry of my Anso Neo has a forward belly that encourages push cuts. It’s similar in design to how a scimitar (cimiter) is used in this way. Push into; then pull through.

Consider the Guillotine. Although it cuts straight down, the blade is angled at 45 degrees. That’s a push cut, too.

You’re asking to wedge the blade straight down and through. Even industrial paper cutters don’t do that. They angle through the slice. Neat party trick, but how practical is it?
 
bucketstove said:
Its time to forget everything you know
;):D
Click to expand...

This is the best advice.

One of things I suggest to forget is polishing the bevel, forget about scratch patterns, instead just increase your angle by 0.1 degrees at every step to be certain you are hitting the apex.

To truly push cut paper you need a razor-like edge. That basically requires two things, a low sharpening angle (as low as you can go without hitting the vise) and stropping. The 1000 grit stone leaves a very torn-up apex, especially as you go to lower angles, I would suggest adding 3 micron lapping film. Personally, I go from the 1500 to 1 micron (with the angle increase). If you wanted to strop on the WE, I would use leather strops with 0.5 on one side and the other clean. Personally, I prefer hanging strops.
 
marchone said:
A push cut is a slicing motion. You’re simply slicing into the material, not towards you. The blade geometry of my Anso Neo has a forward belly that encourages push cuts. It’s similar in design to how a scimitar (cimiter) is used in this way. Push into; then pull through.

Consider the Guillotine. Although it cuts straight down, the blade is angled at 45 degrees. That’s a push cut, too.

You’re asking to wedge the blade straight down and through. Even industrial paper cutters don’t do that. They angle through the slice. Neat party trick, but how practical is it?
Click to expand...

An angled blade is a DRAW cut, the Guillotine is angled to be a draw cut, it is not a push cut.
The draw cut has a mechanical advantage aside from any "toothyness" that also provides additional advantage.
 
I disagree. Semantically perhaps. To draw anything (water, for example) is to pull it to you. A Guillotine pushes through from the beginning of the angle.

And yes, the angle provides a mechanical advantage.
 
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I believe that angling the approach of a blade makes the contact patch between the blade and the object smaller. Any of the 3 angles you can tilt the blade, each make the contact patch of the blade smaller. Which increases the point force on the object and makes it easier to separate. Which is why people chop trees at a 45 degree angle. Same with machetes and brush. It's always at an angle so they can have a mechanical advantage in the cut.

There will be a tiny little draw involved as well: The draw is the width of the object being cut. Because the cut will start at one edge of the object. But it's not exactly a draw cut since the blade is not being moved in a drawing motion.

Saying all of this, the idea that we want to do perfect 90 degree cuts seems really silly doesn't it? We are intentionally making it extra difficult. Presumably as a demonstration of how sharp our blades are. But it's "silly" because we're doing things we'd never do.

I guess I need to make a sharpness tester that cuts carrots and tomatoes. :P :P

Brian.
 
Are push and pull interchangeable? As in simply across the material, whether toward or away from you, but not straight down?

Perhaps I'm confusing the terminology.
 
Much like the word Sharp, there is no single definition. When referring to a saw, we use the terms push and pull to refer to the direction perpendicular to the cutting direction where the teeth engage, usually in the away/push direction, but there are saws with the teeth reversed to cut in the towards/pull direction. Similar terminology is used with kitchen knives when referring to the direction of slicing when downward force is applied, but more correctly push-slice or pull-slice.

However, the term push-cut when referring to testing the sharpness of knives means without any slicing, or a so-called 90-90-90 push cut. What seems to be unknown to most people is that an angled blade introduces slicing even though the knife is moving entirely in the cut direction.
 
Understood. The only time I can think of to use that cut would be to bend a rope and push through it. I need to take out a new X-Acto blade and see if it will go through various paper weights.
 
Thanks to all for responding. This is really good info. I will try each of your suggestions.

One thing that makes this a little more challenging is the differences with respect to the information that I have found and been given. While researching this issue, some have advised a very narrow edge, while others have said that they can push cut paper with a 20 degree bevel. Others advised a very refined edge and others say coarser stones than what I have been using will also work.

I wonder part of the problem is that the definition of push cutting that I would like to adhere to, which is best described above by ToddS, is not commonly known or agreed upon.

It's the 90-90-90 cut that bgentry demonstrated at the end of his second video above, but while using one spot on the edge of the blade. Put a dot on your blade near the bevel, and cut straight down starting the cut at the dot on the blade. At the end of the cut, the place on the blade that has been cutting the paper should still be at that dot. Or very close thereto.

I have done this with printer paper. The goal now is to do it with newspaper.
rummels
 
What you are trying to achieve is equivalent to a decent straight razor edge, or a better quality razor blade. There are basically two ways to get there, either use ultra-fine abrasives (eg Naniwa 12k, Shapton 16k, Gokumyo 20k, .25 micron diamond on leather, etc), or burnish the edge with low pressure on larger, smooth abrasives (worn DMT coarse plate, a barbers hone, virtually any natural stone). In any case, stropping on clean linen and leather as we do with a straight razor is usually the key to getting that last bit of keenness required.
 
rummels said:
I have done this with printer paper. The goal now is to do it with newspaper.
rummels
Click to expand...
Hi,
How many millimeters wide are the bevels?

As you try to push cut,
are you resting the blade against your fingers that are holding the newspaper?
Thats the only way i can do it :)

Have you cut the newspaper into squares?
Newspaper usually has a few fuzzy edges which interferes
If paper is bending one way or another also interferes


My suggestion is finish with a microbevel,
two times one stroke per side
at a higher angle
using ultra lightweight edge-into strokes,
no stropping afterwards,

if it doesn't push cut off the stone,
try 5 lightweight passes per side at original angle



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[*] short video showing deburring/microbeveling, has longer full sharpening video, 90 degree push cut off norton india fine ... its ~P400 /35micron, calls it a stupid sharpening trick cause its so coarse , but its useful ;)
nevermind the non-microbevel angle is low, thats just makes it easier
this isn't burnishing
Crossgrain Pushcutting Newsprint off a Norton India Fine - Steel_Drake
 
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