Slicing and pushcutting TP

Jason B.

Jason B.

Knifemaker / Craftsman / Service Provider
Joined
Jun 13, 2007
Messages
11,196
In our quest to find the sharpest edge we must also find ways to test it. Many rely on the shave test or the paper slicing test and others go to more extremes like splitting hairs or slicing TP. I never thought much of testing the sharpness of my blades until I joined BF, I just always sharpened to a point I was happy with and went about my business. I discovered hair splitting when I became a member and decided to see what it would take for my blades to do that, I found that I needed to use more control and some finer finishes but in the end got what I was after.

Once again an new test has come up and I too wanted to see what it would take for a edge to do this. At first I thought its not really possible because the fibers would just rip apart before cutting or that it would need to be done by a straight razor but after seeing Jim's vid's I knew it was possible. So I grabbed some TP from the bathroom and failed with nearly every single knife I tried :( I didn't really understand because some of these blades were ultra refined and stupid sharp but all they would do is just tear the TP. It was cheap stuff so I figured I'd try something different. I picked up a pack of charmin seeing that it was the preferred test media.

I instantly was able to slice and slice/pushcut the charmin and was very happy but noticed a few things. First, the direction of cut either with the grain (perforated edge to perforated edge) or against the grain (smooth edge to smooth edge) could make a big difference in the cut. Second, the edge did not have to be all that sharp to do it.

Its a cool test no doubt but not one I'd mark down for the record books and for this reason.

The edge, 600 mesh Fine DMT. The knife, CS AK-47 AUS8.
Picture1698.jpg


The Vid, First cut against the grain, second cut with the grain.

[URL=http://s284.photobucket.com/albums/ll20/knifenut1013/?action=view&current=Picture1699.mp4][/URL]
 
No charmin here but I have also found that cheap stuff is harder to slice than the more expensive kind.

Especially on rainy days.

Oh and this one I did with just the factory edge touched up with a few strokes on the sharpmaker. It's not pushcutting but I saved on TP nevertheless. ;)

[youtube]Q_lvstApk80[/youtube]
 
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I think your missing the point ;) Its not the edge its the TP.
 
knifenut1013 said:
I think your missing the point ;) Its not the edge its the TP.
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I actually got the point. I showed that vid because it's been said that only a very polished and sharp edge can do the TP slicing thing. That is a factory edge just touched up. That edge can't even whittle hair. And yes, I also mentioned that I find it easier to slice the pricier kinds of TP.
 
5.56 said:
Yes no two TP's are alike, neither are human hairs. What do you suggest we use?
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The softest most durable stuff you can find.

Oh, for edge testing? Well, I think the importance of the idea is having a standard for use as both a benchmark and as a comparison among forum members. Of course, with reports that slicing direction and humidity matter, we'll all need to keep our red labeled Charmin in an environmentally controlled humidor and make sure we slice in the same direction.
 
I think I'll just keep using toilet paper the way that I have been using it, and not be so anal about my edges.
 
I do the paper cutting: push cut and slice, and the arm hair shave. if my knife can do these things then I consider it sharp.
 
What do we use? I use my fingers and eyes to tell me when a edge is at the point I want it. We use objects to judge cutting ability but is that a judge of sharpness?

You can cut anything you want but you just can't cut it and say wow that cut good. the end. When you start cutting things sharpness is not the only factor as was shown above. Hair? hair is a good test of edge smoothness and refined edge cutting abilities but that too must be looked at closely to be judged correctly.

Directional slicing? Yes it matters, the angle of contact and the structure of the object being cut all matter when trying to cut. If you look at the charmin TP it will have a direction grain like wood as described in my first post. A simple test of pulling the TP apart from the different directions will show you this. Like splitting a log the TP will want to tear apart under pressure of the cut making it easier to cut but not as clean. When cutting against the grain the cut is cleaner but with more noticeable resistance.

Sharpness and cutting ability are two different things and at times can be totally irrelevant to each other.
 
knifenut1013 said:
What do we use? I use my fingers and eyes to tell me when a edge is at the point I want it. We use objects to judge cutting ability but is that a judge of sharpness?

You can cut anything you want but you just can't cut it and say wow that cut good. the end. When you start cutting things sharpness is not the only factor as was shown above. Hair? hair is a good test of edge smoothness and refined edge cutting abilities but that too must be looked at closely to be judged correctly.

Directional slicing? Yes it matters, the angle of contact and the structure of the object being cut all matter when trying to cut. If you look at the charmin TP it will have a direction grain like wood as described in my first post. A simple test of pulling the TP apart from the different directions will show you this. Like splitting a log the TP will want to tear apart under pressure of the cut making it easier to cut but not as clean. When cutting against the grain the cut is cleaner but with more noticeable resistance.

Sharpness and cutting ability are two different things and at times can be totally irrelevant to each other.
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Well, of course... I've cut plenty of cheese with guitar string, but guitar string isn't sharp. In all reality, 90% of the knives that I see that "still cut" have a well pronounced radius over the edge that you can see with the naked eye, and only cut because they're still so thin.

There's still a lot of ways it's useful to indicate how sharp an edge is by how well it cuts or the characteristics of the cut. I mean, when people push-cut and slice note-book paper, are they satisfied when the paper is very rough, with burrs and fibers sticking off the cut? Is that "sharp", or do they take it up until the cut leaves the edges clean?

I don't think the TP test ever began with the notion of, "Oh, this edge can cut TP... It must be very sharp." Lots of people have replicated TP slicing with coarse edges, but how many have had truly smooth and clean cuts. As far as I've seen, only Ankerson's with the 6000 grit EdgePro tape has been slicing TP clean, and has repeatedly said that it won't cut it cleanly unless it's very polished. So far I haven't seen a convincing counter argument to that, so it seems like a good way to test the polish of the edge.

I agree with you and see where you're coming from, but I don't think it really makes the TP test any less useful. I mean, I don't think hair splittings is a very good test methodology anymore either after some of my own recent results that would split hair but wouldn't shave. Then there's the fact that hair varies in thickness, hardness, color, and even the condition. Any time I went to pluck a hair out of my beard, I would have to make sure it was a thick black one with no cinks in it so that the testing was consistent. At least with toilet paper ( regardless of brand ) you're using a testing medium that is a lot more consistent.
 
I typically will push cut thread on a scale. I've seen lots of people use this, and in my "shop" (kitchen) its very consistent. However, my results do not mesh well with others and thus I cannot compare my results w/ thread cutting to anyone else. The same goes for rope, cardboard, leather, etc. At this point, the only tests that can be compared on different days on different knives are the CATRA tests, and even they have a huge number of variables that must all be the same except the one variable you want to investigate. All the at-home tests are basically relative tests for each person to use within their own shops.
 
I've settled into the habit of checking edges in a sequence, something like:

1. First, basic test, is to just cut paper (any paper, but usually start with printer paper) without any significant snagging or tearing.

2. Assuming I've progressed beyond the first test, I'll then see how well it'll cut some thinner paper, like newsprint or catalog/phonebook pages. If it does, then it comes down to:

3. How smoothly/quietly does it cut the thinner paper? I've noticed, with a REALLY good edge, it's almost whisper-quiet. All the more so with a polished and/or convexed edge with nice, smooth shoulders. Next would be:

4. How does it draw cut? Does it slice cleanly & quietly along the complete length of the cutting edge, from ricasso to tip? If it does, then by this point, the next step usually takes care of itself:

5. True push cut. Edge perpendicular to the paper, push straight down into the paper, no slicing or angling/drawing the cut.

If I get that far, I'm usually satisfied. I'll still check for shaving and/or hair whittling/tree-topping, but won't worry too much if it's not quite there. I know at this point, the edge is a truly useful one for real work.
 
I have seen in threads where it was stated that if you can slice TP you can whittle hair. I've also seen the push cut of TP labled as the ultimate in sharpness. Nither of which are true but many still believe it to be.

Sure you can look at the quality of the cut but some of these vids with high polished edges are not making as clean of a cut as my 600 edge. Does this mean my knife is sharper? probably not. Tomorrow I'll put up some shots of the sliced TP at different grits.

Kenny, you made a good example. Cutting cheese with a guitar string, think about that one for a while.
 
knifenut1013 said:
I have seen in threads where it was stated that if you can slice TP you can whittle hair. I've also seen the push cut of TP labled as the ultimate in sharpness. Nither of which are true but many still believe it to be.

Sure you can look at the quality of the cut but some of these vids with high polished edges are not making as clean of a cut as my 600 edge. Does this mean my knife is sharper? probably not. Tomorrow I'll put up some shots of the sliced TP at different grits.

Kenny, you made a good example. Cutting cheese with a guitar string, think about that one for a while.
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I always cut against the grain for more resistance.

It's more about how clean it cuts and with no TP stuck to the edge. ;)

I have said that more than a few times in threads.

I have taken some Spyderco Knives out of the box and they sliced TP with the factory edges, but not clean.

It's one of my tests that I do, and once it will slice it clean it will Whittle coarse Hair easy. Has to be clean like it was cut with scissors.

To push cut it clean must whittle my extremely fine hair then it's getting there. (That level of sharpness is gone after one or two cuts through TP, it won't whittle the fine hair anymore.)

Just depends on what you are looking for.

Also why in my videos I show the cut TP after it's cut to show it was clean.
 
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Hey Jim, can't get back to the PM's at this time my smart phone is not smart enough. I did notice a few of those things with the different blades I tried.

I think "tests" need to be explained though, too often you see great displays that are followed by abstract thought of the less informed. Kinda like when you hear "I chipped my blade" and its not really a chip.
 
Obsessed with Edges said:
I've settled into the habit of checking edges in a sequence, something like:

1. First, basic test, is to just cut paper (any paper, but usually start with printer paper) without any significant snagging or tearing.

2. Assuming I've progressed beyond the first test, I'll then see how well it'll cut some thinner paper, like newsprint or catalog/phonebook pages. If it does, then it comes down to:

3. How smoothly/quietly does it cut the thinner paper? I've noticed, with a REALLY good edge, it's almost whisper-quiet. All the more so with a polished and/or convexed edge with nice, smooth shoulders. Next would be:

4. How does it draw cut? Does it slice cleanly & quietly along the complete length of the cutting edge, from ricasso to tip? If it does, then by this point, the next step usually takes care of itself:

5. True push cut. Edge perpendicular to the paper, push straight down into the paper, no slicing or angling/drawing the cut.

If I get that far, I'm usually satisfied. I'll still check for shaving and/or hair whittling/tree-topping, but won't worry too much if it's not quite there. I know at this point, the edge is a truly useful one for real work.
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I like your scale- I think it matches closely with my own personal standards, although now I'm going to have to add the push cut as a new personal goal. Way to go :p
 
KennyB said:
my own recent results that would split hair but wouldn't shave.
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don't get that.

splitting hair is cutting it, how can a knife cut into a hair but can't cut it off your skin ???

or you have a residual burr and you've splitted the hair with the sharp burr but shaved in the wrong direction ? like when a knife shaves but only in one direction ?


thanks.
 
Aren't we starting to get a bit ridiculous with this level of sharpness? I mean, I sharpened my Para2 enough to pop hairs, but a couple of slices through cardboard and I completely lost that sharpness. I only see it as worth the effort with light cutting in the kitchen.
 
This thread is not so much about sharpness as it is about why things cut the way they do. The test we use to judge our sharpness are what is in question and as you can see sharpness is not the deciding factor in the edges ability to cut TP.

If your happy with your edge then that's good enough but hopefully its been constructed properly. What I mean by this is say you finish with a 1k stone, do you have a 1k edge? or a edge roughed by a 1k stone?
 
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