Push/Pull Cut

[tim8557]

I guess that the name describes the action, but what is the significance when discussed in relation to testing a knife?

 

[Quiet Storm]

A fine edge lends itself to push cutting while a coarser, micro-serrated edge is more suitable for pull-cutting.

 

[tim8557]

Thanks. I see Cliff and others refer to it, but never understood the diff.

 

[DGG]

A fine edge lends itself to push cutting while a coarser, micro-serrated edge is more suitable for pull-cutting.

How does it relate to real world use in your opinion? I think I can profile a knife to imitate a razor and it will push/pull cut very well but won't be worth a darn as far as a usable tool.

In otherwords can a blade be "too sharp"?

 

[Quiet Storm]

I'm by no means an expert, but some tasks require the bite of a micro-serrated edge. Cutting fibrous materials is much easier with a coarser edge. A fine edge will not pull cut rope as effortlessly, but it will handle most other tasks far better. It's largely a matter of personal preference, depnding on the materials you regularly cut.

 

[Cliff Stamp]

In otherwords can a blade be "too sharp"?

No, but the profile can be too thin.

There is always a tradeoff of cutting ability vs durability, as you increase the cutting ability of a knife you lower its scope of work, what it can do without damage. However what is required with quality steels cross section wise is far lower than usually promoted.

I run my regular EDC knives at ~5 degrees per side, the only things I don't cut with them are metals and bone, I will work around bone, just not attempt to cut through it. If I need a knife to cut light metals (food cans) and light bone (chicken) I use ~10 degrees per side.

Technique makes a large difference as does quality of steel. The more work you do, typically the less you require of the knife to be able to do it. You also need fairly decent steels to even tolerate low angles and form cleanly let alone function with them.

I have knives with heavier angles, heavier choppers which can see rock impacts go about 15 degrees, and utility tools which are essentially sharpened prybars run ~20 degrees.

-Cliff

 

[ginshun]

No, but the profile can be too thin.

There is always a tradeoff of cutting ability vs durability, as you increase the cutting ability of a knife you lower its scope of work, what it can do without damage. However what is required with quality steels cross section wise is far lower than usually promoted.

I run my regular EDC knives at ~5 degrees per side, the only things I don't cut with them are metals and bone, I will work around bone, just not attempt to cut through it. If I need a knife to cut light metals (food cans) and light bone (chicken) I use ~10 degrees per side.

Technique makes a large difference as does quality of steel. The more work you do, typically the less you require of the knife to be able to do it. You also need fairly decent steels to even tolerate low angles and form cleanly let alone function with them.

I have knives with heavier angles, heavier choppers which can see rock impacts go about 15 degrees, and utility tools which are essentially sharpened prybars run ~20 degrees.

-Cliff

Your talking per side with all of those angles correct?

even then, its still seams like the angels are more acute that what I usually see in FAQ's and around.

You mention good steel is needed to handle these angles. Which steels? I assume 154CM, ATS-34, VG-10 and the like are all fine? I would think 440C and AUS 8 would be fine too, but I would like you to confirm. Don't think I have any knives with lesser steels than those anyway.

When you sharpen a knife down to 5 or 10 degrees per side, do you leave the edge at that angle, or do you put a more obtuse microbevel on the edge?

I use a Lansky to sharpen usually so I can't even get down that far. The instructions reccomend that he 17 (which is the lowest angle) is for things like Xacto knives and such. This alwasy seemed a little odd to me too, but i have just recently been looking into sharpening a lot more.

I am thinking of trying a 17 degree primary with 20 edge on a couple of knives. The way it sounds, this should be fine for every day use on a knife with a decent steel right?

 

[tim8557]

I'm at the point where most of my knives have a secondary at less than 15 degrees and a primary at 15 degrees per side; as measured on my Edge Pro.

My knives, I admit, don't really see hard work (bones, metal, rocks; generally paper, cardboard the normal things knives, I suspect, are genrally used for.

 

[Cliff Stamp]

Your talking per side with all of those angles correct?

Yes.

...the angels are more acute that what I usually see in FAQ's and around.

Yes. My preferences came from reading posts by Alvin Johnson and Mike Swaim on rec.knives and repeating their work and coming to the same conclusions.

You mention good steel is needed to handle these angles. Which steels? I assume 154CM, ATS-34, VG-10 and the like are all fine? I would think 440C and AUS 8 would be fine too, but I would like you to confirm.

154CM and some of the other stainless is that they are fairly coarse grained and thus can break apart at low angles and thus the edge can be a little coarse, a micro-bevel solves this problem competely though.

When you sharpen a knife down to 5 or 10 degrees per side, do you leave the edge at that angle, or do you put a more obtuse microbevel on the edge?

Microbevel, a few passes per side, not really because it needs it as much as much as my freehand sharpening skills are not overly great. A tiny micro-bevel does make it much more durable though, and raises ease of sharpening significantly.

I recut the primary when I can see the micro-bevel. It never gets so thick that it requires more than 10 passes per side on the medium Sharpmaker rods to reset the edge when blunted down to <10% of optimal sharpness.

I am thinking of trying a 17 degree primary with 20 edge on a couple of knives. The way it sounds, this should be fine for every day use on a knife with a decent steel right?

Yes, that should be a very durable edge even on fairly low end steels, felling axes for example don't have edges that obtuse.

-Cliff

 

[Jeff Clark]

I tolerate the term "push cutting", but I think "pull cutting" is horrible terminology. I generally think in terms like "dicing" and "slicing" as you would use the terms in a kitchen. When you dice you press straight down with your blade or perform a light chopping action. The key aspect is that you don't slide your blade across the material, you are "pushing" straight through. Slicing is what you do with a roast or a turkey. You draw your edge across the material a bit like a sawing action. So I much prefer to talk about that blade action as "slicing".

With a short knife you almost always get some crosswise edge motion as you cut. For that reason I always want a knife with good slicing performance. This requires either a very fine accute edge or a fine edge that has a little bit of microserration to it (or you could use serrations). If I don't hone my edge to under 10 degrees per side then I intentionally finish the edge with a slightly rough hone. If I have an edge as obtuse as 20 degrees per side I may finish it with a file.

 

[ginshun]

Thanks Cliff!!


And I have found that for some reason putting the microbevel on the edge just gets the knife much sharper. I used to just sharpen most of my knives to to 20 degree slot on the Lansky. They would come out decently sharp, but not overly so. Lately I have done the same sharpening, only after I am finished I went over it for a few passes from the 25 degree slot. The blade seems to get much sharper.

Does this seem right to you guys or am I crazy? If is makes sense, why does it work like that? It just doesn't seem right. Intuitively, it doesn't seem like putting a more obtuse angle on the edge would make the knife sharper. It sure seems to though.

 

[Cliff Stamp]

Intuitively, it doesn't seem like putting a more obtuse angle on the edge would make the knife sharper.

You are likely minimizing the burr.

-Cliff

 

[ginshun]

You are likely minimizing the burr.

-Cliff

Fair enough, all I know is that it works. Thanks for all the help. I am going to take one of my common EDC's down to 17 and 20 tonight and see how it works.

 

[Zerileous]

I would agree with most of what is said here. I do tend to keep my knives at a low angle. With spyderco knives, I usually keep it a tad under 30* inclusive. I am going to experiment with some lower angles though. Some knives like my native, which I do wiring on, will stay all the way up at 30*, because I cut copper wire alot with it. Also, I someitmes like to have a tough and obtuse edge, for example, I was riding my bike and had to cut some shifter cable. Hard steel cable. Not a good knife task but it was the only way to get home, and I knew I could fix the edge in less time than it would take me to walk. If i had had a 10* incusive edge on my paramilitary, I doubt I could have done that.

I guess my point is that on some of my larger knives, I feel the need to find a balance that is an excelent cutting edge for general soft tasks, but still has the strenghth to pull through when the **** hits the fan. I think that is under 30* for s30v, but I am not sure how thin I should really go. Keep in mind I use bench stones, so I cant be exact, but I can guesstimate decently. Some knives like the salsa and calypso jr will be getting very thin edges, but for larger knives, I want something very fucntional for EDC yet capable of more.

 

[Jeff Clark]

When you work with thin materials (and your edge is extremely thin when you are finishing it) funny things happen. The material that you are trying to abrade bends away from your hone. You may think that when you hone at 10 degrees you are cleanly cutting the material at that angle, but that is not true right near the apex. You can observe this effect if you try and grind a very thin point on a thin steel rod. You don't simply get a burr of foil-like material folding away from you. That is from material that has exceeded its plastic deformation limit and flopped around the edge as you worked. You also have some material that has bent away from you elastically as you worked. As soon as you release your pressure against the hone this material straightens up and some of it swings back into the area where you thought you had removed everything.

Instead of the honed surfaces coming together in a nice narrow 'V', the V can kind of bulge at the bottom or can be sitting on top of a narrow post. This isn't what I consider a true burr since it will be pretty symmetrical and made from sound material, but it also isn't what I want for a maximally sharp edge. To get rid of this material you need to compensate for the tendency of the edge to bend away from you elastically as you hone. Honing extremely lightly helps a little, but it is better if you also increase your honing angle slightly to precompensate for that edge-leaning phenomenon. If you look at the finished edge after doing a few light microbevel strokes at a slightly higher angle you will not see a microbevel. What you will see is what you wanted in the first place, a single accute bevel that goes all the way to the edge.

ColoradoDave ran some great tests that examined this phenomenon a while back. Everybody should read it.
http://www.bladeforums.com/forums/showthread.php?t=305456

 

[nelsonmc]

I sharpen my knives with a stone or crock sticks, and I've never seen a point in getting too technical about it. Push, pull, 5°, 30°, micro-bevel, they mean nothing to me personally. I want to enjoy sharpening and not figuring out a formula before and during. Practice makes perfect, some people spend hours getting the perfect bragging edge, some spend 2 minutes, and some of those 2 minute sessions hold an edge just as long or longer than the more complex ones. Anyways, to each his own, but I "use" my knives, I have no reason to split a hair or show off.

Gosh I hope this post doesn't insult anybody, it's honestly not meant to be.

 

[Cliff Stamp]

I sharpen my knives with a stone or crock sticks, and I've never seen a point in getting too technical about it.

Depends the importance of performance, one you start looking for it you have to spend a lot of time on sharpening because it doesn't make a lot of sense to spend $300 on a knife and use it with a stock edge when a $5 knife with a better sharpening job out cuts and out lasts it.

In regards to "just using them", a vast amount of what is commonly accepted now in regards to sharpening and performance in relation to sharpening was explored by Mike Swaim as he worked in a fish plant and experimented with sharpening.

He was just a guy using a knife for a living and wanting a way to make it easier / more efficient. There are various techniques and approaches that can improve cutting ability, edge retention and ease of sharpening by easily a factor of 10, so if performance is important then they are worth looking into.

-Cliff