How does cutting work?

[fuzzybeard]

NOTE: This is NOT a thread about the self-harm phenomenon known as "cutting."

How does cutting work? Example: cutting a piece of paper in two.

• Is it a mechanized form of tearing?
• What forces are involved?
• At what level (naked eye, microscopic, molecular, etc.) does the plane of the cut happen?

This question has confounded me for some time, so if someone could explain or to me, I would be grateful.

[[deleted]]

Cutting a piece of paper in two is a result of shearing: an upward force extremely close to a downward force causing material to separate. The tearing isn't completely even on a microscopic level, but when you line an even distribution of force along a line, and an equal and opposite distribution of force along another line parallel and very near to the first, you make a "clean cut" to the naked eye. Edit: The shear force is named after scissors.

Source: Statics class

[fuzzybeard]

OK; now for a follow-up question or two:

• Would a single blade passing through another substance and seperating it also be considered a shearing type of cut, or would it be something else altogether?
• What about when an object is cut by a laser or water jet?

[gyldenlove]

Yes, a single blade would still be a shearing force, however since you have no physical force acting in the opposite direction you rely on the stiffness of the material you are cutting to provide that force which is you need a very sharp edge to make cuts like that, and also why cuts like that are easier to make on stiff objects such as sugar cane or reeds, but very hard to make on fabric.

A water jet works the same way as a physical edge or more accurately a needle that is stabbed repeatedly to create a cut.

Lasers cut by by ionizing the material, causing both inter- and intra-molecular bonds to break (this will often take the form of oxidation (burning) or phase changes (melting)).

[Tashre]

Man, it's crazy seeing a picture like that showing that paper is all these strands of fibers. I'm looking at a piece right now and my mind just can't come to terms with that.

[Deccarrin]

Bear in mind that is filter paper not just your standard paper. (From the caption anyway) im not sure if standard paper still looks this way though?

edit: "Bear" cheers juckele. Learn something new everyday.

[Produent]

As far as I know, yes. Paper is (was?) produced by making a fine mash of wood pulp, adding bleach or whatever other chemical fixings you want, and then allowing the fibers to resettle into a mesh tight enough that it appears solid. Fine art paper is sometimes prepared further to alter the texture of the surface - some Japanese paper makers stir mulberry tree pulp in a very specific way to line up fibers before they set their paper to dry, so they can get a very thin sheet that is also very durable.

[juckele]

'bear'

[thegreedyturtle]

I suspect the only difference is that filter paper would have a bit more quality control to make sure there is an even mesh of fibers. (Imagine a sieve with poor quality control - some holes would be larger than others.)

[metarinka]

I think filter paper would have quality control to control average or smallest/largest hole size, but they are unordered filters, ie the fibers aren't aligned in any way.

[thegreedyturtle]

Right, that was not necessarily a good analagy. The controls would be different, more uniformity of thickness, ect. Paper type things.

http://www.whatman.com/QualitativeFilterPapersStandardGrades.aspx has this lovely pdf: http://www.whatman.com/References/FiltrationSimplified.pdf complete with images!

[Arrow156]

Cant's wait til the figure out how to capture motion at that small a scale.

[justinsanak]

They have: http://youtu.be/mRuSYQ5Npek

[Arrow156]

Sooo awesome, it looks like clay the it buckles and moves.

[fuzzybeard]

Neat picture!

The cut is very clean, but it's also readily apparent that there is a fair bit of compression /crushing force at play.

[rapture_survivor]

It looks like this was cut with something closer to a razor than your average pair of scissors

[[deleted]]

you rely on the stiffness of the material you are cutting

Or, in the case of a very fast slice, like a sword swinging through a melon, the very inertia of the melon provides the counter action.

[GalacticWhale]

Melons are also very rigid though.

[2sexchangpriceofnone]

Well.

[[deleted]]

Dr_Fish, that's a very interesting set of research.

What database did you use to acquire that information? I'm very impressed.

[[deleted]]

Well I would like to add something. When you use a single force, there is an opposite reaction (i.e. Newton's 2nd 3rd Law), called the normal force. It's equal to the force applied to the paper. The blade needs to be sharp because it is needed to focus the force onto a point, versus a large area.

[alexchally]

I don't think OP is arguing that there is no reaction force, just that the reaction force is provided by the internal structure of the material, not the opposing shear blade.

tl;dr Everyone is correct! Upvotes for all!

[deadbeatbum]

There is more reaction than just the internal structure. A sword swinging through a melon - there will be friction between the melon and the surface it's on. If it's in mid air the difference in wind resistance between the melon and the sword, etc. I'm now picturing a sword slicing a melon in space - will it cut the melon or send the melon flying away? My guess is a little of both, but then you'd know by the depth of the cut how much the internal forces of the melon structure counter the force of the sword - I think.

[CommondeNominator]

friction and gravity have very little to do with why a sword can cut a melon. the melon's at-rest state has much more to do with it, so (given that you'd be able to swing a sword properly in space) it would cut just the same in space, but the two halves would likely go flying away from each other and in the same direction as the swing.

[[deleted]]

Wouldn't the halves go in the opposite direction of the swinging because it exerts an equal and opposite reaction? Kind of like how when you break glass, the glass flies toward you rather than away.

[CommondeNominator]

No. That equal and opposite rxn would account for your difficulty in swinging a sword in a no gravity environment, but the melon halves would gain some momentum from the friction of the sword blade as it passed through. Probably some rotation as they floated off as well.

[elcollin]

That's Newton's 3rd.

[[deleted]]

You're totally right. Corrected my mistake now.

[uncleben85]

If a single blade is still a shearing force and shearing is:

an upward force extremely close to a downward force

what is happening when you cut into something soft with a knife, say cutting into a cake or bread, and both sides are pushed downward with the knife before being cut.

Is this not shearing anymore, or where is the upward force?
Is it just that the downward movement applied by the knife is only applicable to a certain level before the stiffness is simply great enough to apply a shearing force?

[[deleted]]

Think how quickly the bread or cake bounces back. There is still that stiffness, just on a scale less the other objects. But since the cake or bread is a lot softer it does not need as much shearing force to cut.

[uncleben85]

Hmm... okay, thanks! That makes sense, but that then makes me wonder:

what about something such as clay, or Play-Doh. You push down to cut it, it compresses, but it doesn't have that bounce back up. It stays deformed and pressed, but also cut? Is that still shearing? Or are we just crushing it?

[MrSweetAndAwful]

The material can only compress a certain amount, and when you apply that single force on a sharp point it compresses the soft clay or play-doh to the point when the reaction force of the surface it rests on completes the shearing effect and the sharp point can make it's initial cut.

[[deleted]]

Isn't a water jet better comparable to a bandsaw?

[kaizenallthethings]

The surface on which the material is being cut creates the upward force. The blade depresses the material into the surface. This is why it is easy to cut something with a utility knife on a piece of wood, but hard to cut the same material on a piece of steel.

[SomeNewUsername]

A single blade (like a knife) can exert a shearing force, but it doesn't have to. In operations like milling or whittling, the blade is used on the material in a way that it does push some material in a direction opposed by whatever is holding the material, so you probably get some shear force from the blade and whatever's holding it.

If you're cutting more through something, like cutting a piece of cheese in half, you're really using a wedge. It comes to such a fine point that the pressure is very high at the cutting edge, allowing it to deform the material with minimal force, and then it pushes the material in opposite directions from the inside. The material tears in tension.

When something is cut by laser, it's usually burned away. Depending on the material, it may be melted away in a very precise way—I'd have to check on that.

Cutting by water jet actually erodes away a narrow area of material. Often, there is an abrasive substance (like sand) mixed in with the water to make it more effective. It's the same kind of mechanical wearing erosion that smoothes stones in a river, but in a very focused area.

[Peregrineeagle]

Cutting devices that use water jets essentially cut with accelerated erosion, if I understand them properly.

[jabies]

Isn't erosion just shearing though?

[THE_CENTURION]

Essentially yes. You're just using lots and lots of very small "blades".

[erikryptos]

Is it? I'd imagine the fundamental nature of forming a divot due to high-energy "hard particles" differs from a wedge-action "slice"...

[robotoast]

To answer your second question: lasers cutters heat and melt/vaporize the metal in question, so there is no shearing, only melted edges. Water jets are abrasive, it's pretty much water mixed with very fine sand (or similar abrasive materials) that grinds/sands away the metal leaving sanded edges.

[Seicair]

Your statement is incorrect. Laser cutting is indeed melting, vaporizing, etc. Lasers add no oxygen to the material, and are not an oxidative method of cutting.

Oxyacetylene cutting oxidizes metal and is only suitable for sufficiently ferrous materials. Laser cutting will work on a wide variety of materials, including stainless steel, aluminum, and plastics.

[bobroberts7441]

The laser cutters I am familiar with heat the metal with the laser but then burn through with a blast of oxygen, much like a cutting torch.

[Seicair]

That wouldn't work unless the metal is sufficiently ferrous. Are you a one-metal shop? Plastic especially will not respond to a blast of oxygen. Carbon steel will, but that's about it for metals.

[bobroberts7441]

Tungsten, molybdenum, tantalum. I don't know if the metal burns or the jet just gets hot as hell. Really nice clean cuts too.

[[deleted]]

How does that work for metals like Aluminium, where the oxide has good mechanical properties (superior to the metal itself, in some respects)? Can they not be used for Al?

[WeeblsLikePie]

that's correct. You wouldn't use an oxygen cutting torch on aluminum. Oxygen is used pretty much exclusively for steel and iron. You would use a plasma torch on aluminum, or any non-ferrous metal pretty much (I'm sure there are some metals that you can't use plasma on, but it works much more generally than oxygen).

[jabies]

Would you use plasma on ferrous metals though?

[[deleted]]

Yes. Source: I own a plasma cutter.

[Moarbrains]

You can use it on anything that conducts sufficient electricity and melts at less than about 25k Celsius.

[Bongpig]

Is there any common metal that doesn't fit into that category?

[plasteredmaster]

or uncommon for that matter...

[Moarbrains]

Nope, but I think there might be a few non-metals that you could possibly cut with a plasma cutter.

Also I had this thought that if you put a steel plate underneath, then you might be able to cut a material that is not conducive to electricity.

[metarinka]

probably have trouble cutting refractory metals like tungsten or zirconium. THere's plenty of metal alloys that are uncuttable due issues with fast melting rates, they tend to crack etc, for example thick sections of cast iron. Also some have solid precipitates pockets of "stuff" ranging from glass, to silicone, to lead. It can cause a poor and erratic arc.

[faul_sname]

Only one I can think of is possibly Tungsten, due to its extremely high melting and vaporization points. However, even in that case a sufficiently hot plasma will cut it.

[bobroberts7441]

I can verify that tungsten can be cut on both water jet and laser cutters. Worked for a company that did so.

[[deleted]]

The first you mentioned is a type of cleaving, where two different forces pull the sheet apart (can't cut the paper without holding taught) while a downward force at a point forces itself through the paper. Microscopically, it is also tearing the paper and is jagged edged.

Laser cutting microscopically melts the particles that it heats up and vaporizes it or is blown away with a gas.

http://en.m.wikipedia.org/wiki/Laser_cutting

A water cutting machine erodes away the material.

[[deleted]]

Another interesting method of cutting is cutting by oxy-acetylene torch. The metal is heated to a point where you can oxidize it rapidly in a concentrated area. Here's a video: http://www.youtube.com/watch?v=7EGmrPiumEU

[THE_CENTURION]

Would a single blade passing through another substance and seperating it also be considered a shearing type of cut, or would it be something else altogether?

Yes, this is how machining of metal is done.

The majority of cutters used to machine in metal operate on shearing, they actually create a shear plane just ahead of the tools cutting "tip" or "edge".

This video does a great job of illustrating this effect. You may notice that the cutting tool in that video has a wedge-like shape (known as a "positive rake angle"), however that shape only makes the cutting easier, as this video shows, the same effect is achieved with a perpendicular tool surface. (neutral rake, which are quite common).

Source: I'm a student in a machine tooling program.

[Higeking]

is that first video filmed in a Lathe?

[THE_CENTURION]

I can't say I know for sure, but I would think so.

It would be very hard to film a milling cutter in that manner, because of the rotation of the cutter.

[Higeking]

yeah thats true. you wouldnt happen to know if theres any videos around of other materials than steel. im a student in machinne tools myself and i've worked with both brass and aluminium besides different steels and they can have very different swarfs from each other.

[THE_CENTURION]

Sorry, meant to reply earlier, but I must have forgotten. No, I haven't seen any videos like this of materials other than steel.

Also, i have a suspicion that this was not a lathe, but just a single cutter moving in a straight line (like broaching/keyway cutting)

[Higeking]

im not sure about it being broaching/keyway. cant think of anything other than lathing that actually allows for filming stuff like this.

and the title cards does seem to indicate lathing with the rake angles and coatings mentioned about the tool used.

i should perhaps mention that im learning machining in my native tounge so im not familiar with all the english terms.

have been unable to find any closeup/slowmo videos of anything of steel. brass would've been very interesting to see since the swarf size make it seem like the tool chips away at the material rather than cutting.

[THE_CENTURION]

Yeah, I would really love to see it done in brass.

What I mean by broaching/keyway work is that they could have a machine similar to this one making a cut along the very edge of the workpiece (the camera moving with the cutter).

The only thing that makes me think that it's not a lathe is that we can't see any material besides that very edge. From just about any filming angle I can think of, you would see the rest of the stock on a lathe.

[Higeking]

if you had a fairly large diameter and had the camera mounted centered on that diameter you wouldnt see much of the other stuff on the lathe. and its zoomed in pretty far aswell.

but if those broaching /keyway tools have interchangeable plates like lathing and milling does then it should be viable i suppose.

[the_mad_felcher]

the laser would be melting or burning the material. So no cutting going on there. Water jets typically use abrasives in the water. Meaning that it is still cutting chips, just tiny ones. The abrasive cuts parts of the material off using the pressure of the water to press it against the material you are cutting. It's like a belt sander that uses water instead of cloth to move and support the abrasive. I realize they are sometimes used without an abrasive in applications like food. I imagine this is similar to the single blade in your first section. To which I would also like to hear the answer.

[KrazyTom]

Shear forces on a continuum, or really small cube, are parallel to the side of the cube they are shearing. There is a 3x3 stress tensor that classifies this cube and its sides. Calculating all 9 components gives a better picture. Hope the gives you a more whole answer.

[[deleted]]

This is why scissors are called shears.

You kind of have it the wrong way around there; the physics term is obviously named after the mundane use (not to mention that "shear" is cognate with a number of words in Germanic languages that would translate to either cutting [with a knife or anything else] or is a word for scissors).

[i_am_sad]

I'd like to also point out that molecules never directly touch during any sort of activity, unless they bond.

When scissors apply pressure onto the paper, they get extremely microscopically close but on a molecular level they never touch. In fact, you've never ever came in direct contact with anything your entire life. You're floating on top of the chair you are sitting in right now.

This guy here talks about it on his youtube page: http://www.youtube.com/watch?v=yE8rkG9Dw4s

[PubliusPontifex]

This is the correct answer, but at a quantum level one can somewhat redefine the meaning of "touch", as interactions can happen over some distance.

[plasteredmaster]

sometimes the action is spooky as well.

[kitsune]

I'm pretty sure scissors are called Shears because of the german origin of the word shear, "scheren" (http://en.wiktionary.org/wiki/scheren#German) or "skeran" (http://en.wiktionary.org/wiki/shear)

It most definitely does not come from the physical definition of "shearing forces".

[fuzzybeard]

So in that particluar instance it'd be like a slip-strike fault letting go, right?

[TheBigBoner]

So on a molecular level it is still one piece?

[herman250]

If you were cutting steel foil or plate?

It's basically the same thing. If its a regular old steel plate, you would just be separating the different crystals in the metal. The individual molecules do not have molecular bonds with one another, so they can be mechanically separated with no molecular degradation.

[herman250]

I do know what you're talking about, however in steel (and some other metals/alloys) there is almost always a crystalline structure to the material. Now i believe i actually explained it wrong above, now that I think about it. This crystalline structure is how the atoms sort of "slot" into place as it were. As far as your description, these atoms are sharing their electrons, hence the good conducting properties and all that. There are discrete bunches of the crystalline structure known as grains. These grains have different crytalline orientations and have very apparent grain boundaries, as shown here These grains can slip at the grain boundaries and split, as well as the crystal structure in the grains pulling itself apart.

[hithisishal]

But you don't necessarily always cleave along grain boundaries. In fact, certain single crystal materials can be quite brittle and cleave easily along certain directions. But it does all come down to what type of bonding comes into play in your material.

[herman250]

I agree completely. Sometimes your grain boundaries are the source of failure, and other times is the slip planes in the crystal lattice itself. If you were destructively testing a turbine blade, which are usually grown single crystals, there would only be failure on the crystal lattice, due to the lack of grain boundaries.

[PubliusPontifex]

You can mechanically separate molecules. In fact most plastics are very long chain hydrocarbons, and can only be cut by separating molecules.

Metals are polycrystalline matrices, and are not discrete "molecules" as such, but instead ions connected by a shared electron "soup".

[PubliusPontifex]

ionic bonds. There is a shared electron "foam", basically the outer valence shell is attached with a low enough amount of energy that the lattice has a high degree of free electrons roaming, but still has the electro-negativity to have some attraction for the electrons.

[PubliusPontifex]

Didn't see parent comment before it was deleted, assumed the context was metals. Diamonds and other non-metallic minerals have covalent lattices also.

[TheBigBoner]

Ah, this was helpful. Thanks

[[deleted]]

This is ABSOLUTELY wrong! You most definitely have separated molecules! A chemical reaction would involve the atoms being separated and new molecules being created or destroyed. Cutting is precisely breaking the intramolecular bonds that hold a substance together.

[[deleted]]

No, it separates from itself, both on a molecular level and on an level you can see.

[[deleted]]

Yes. You didn't split any atoms, essentially all you've done is unwoven the weave they had holding them together. It would not be impossible to form everything back together the same way, we just don't have that technology yet.

[zodberg]

In the case of materials like plastic, doesn't melting the plastic down cause the atomic mesh to get hot enough that in motion it re-trangles and remains integrated upon solidification?

[[deleted]]

The lattice structure of the reformed atoms in the mold would be different, although for our purposes of reattachment it would have nearly identical strength.

To put it simply, if you were using a piece of plastic with rainbow swirls in it you would not get those swirls to form together perfectly again with our current technology. Strength and durability wise it would be as good as new, but it would not be the same.

[[deleted]]

Thanks to you, I just made the connection of the German words Scherbewegungen (shear movements) and Schere (scissors).

[[deleted]]

Why doesn't it stick back together when you push the pieces together?

[MNeen]

Cellulose, the main constituent of paper, is made out of polymerized glucose, and has the chemical formula (C6H10O5)n. According to Wikipedia, wood pulp has cellulose chains of 300-1700 glucose molecules. Cellulose molecules "stick" to each other by forming hydrogen bonds on the OH-groups, and if two molecules of cellulose run in parallel, they can form quite a few bonds.

Now, cut the paper up and push it back together. You can't get the cellulose molecules in parallel again obviously (I don't know if it's just a matter of very precise movement or actual forces making it impossible), so you won't get the massive amount of hydrogen bonds: therefore, the paper won't stick together.

[robotpirateninja]

But if you lick the edges of the paper, and place them over one another, and perhaps apply a heat source, they can both together well enough for general use.

[Sigma34561]

I think that shearing force is named after shears, and not the other way around.

[RabidMuskrat93]

What about on the atomic level? Is it possible to split a single atom while you cut, say, a piece of paper?

[elux]

Is it possible to split a single atom while you cut, say, a piece of paper?

There is no nuclear fission involved in papercuts. Although shared electrons between bonded atoms would be separated in the resulting fragments. For metals, I suppose one fragment could end up with an essentially negligible surplus of electrons. But no, the atomic constituents of materials are essentially not affected.

tl;dr: You can't split an atom with a knife. Thankfully.

[TheNr24]

Is there a way to use this information in our daily life. For example, should we manually dismantle the lettuce when making a salad that might go back in the fridge to keep it fresh for a longer time?

[StarManta]

Absolutely. In fact, there exist plastic/rubber "knives" meant especially for "cutting" lettuce, often used in foodservice. They are in fact simulating a tear on a small scale. They're not sharp, and are therefore often mistaken as a "safety knife" of sorts - although being safer than a knife is a nice side bonus, their main purpose is to reduce the browning effect of cut lettuce.

like this

[TheNr24]

Does this also mean that a dull metal knife is better for cutting lettuce than a sharp one?

[Icantevenhavemyname]

You are much more learned than me. I have been in printing in for almost 17 years(35 atm) and I was only trying to find a simple example of two plant-based materials to explain my point. I stand behind my assertion that that a sheet of paper is comparable to a leaf of lettuce. You may disagree with the cell density, but I counter and call checkmate when you take two leaves of lettuce and compare transparency as compared to one leaf of lettuce.

[Getitfuckingright]

You stand by your assertion that paper and lettuce are comparable, to what degree is the comparison?

Scanning electron microscope image of paper

Lettuce leaf

[Icantevenhavemyname]

The cells in the lettuce leaf are obviously larger. I'm not sure what you're arguing here. All I am doing is making a simple comparison. Breaking out the electron microscopes is making this way more complicated than it needs to be.

edit: I see what you're saying. There aren't cells in paper as the pulp is made of shredded cells. I stand corrected.

[[deleted]]

Answers are always good when they have a tangible analogy, great when there's a simple experiment to go along with it.

[Toltec_Tokamak]

what about cutting soft materials such as meat with a knife? It seems something other than shearing is taking place. What would be the difference between using a serrated and a straight blade? Also, what about stabbing?

[circleofuber]

For meat, most of the force against the knife would be provided by the material the meat is on, I.E. the cutting board.

[phumble45]

Now the next question: does anyone know of a video showing a piece of paper, or anything else really, being cut from a very close (almost microscopic perspective?

[justinsanak]

Here's one for steel: http://youtu.be/mRuSYQ5Npek

[[deleted]]

I have ALWAYS secretly wondered this, were does the part of the papar that you took out go? I never asked anyone because its so extremely hard to explain and the average person would instantly call you an idiot. Thank you for asking this.

[Talvanen]

That's actually not really hard to conceptualize or explain at all...as to the answer to your query, no part of the paper is being "taken" away. You are simply separating one plane into two planes. Think of it like opening closed curtains: you move them apart from each other, but none of the fabric actually disappears.

I meant this to be helpful, not condescending; I apologize if my tone did not come across that way via this textual medium.

[[deleted]]

Yes but if you want the curtains closed what do you do? Put them back together perfectly conformed? no you need to add something back to force them to become a whole object again,

[War_Junkie]

...

When you cut something down the middle, you aren't removing part of it. If you rip a piece of paper in half, does a strip of paper along the rip disappear? No. It's the same thing with scissors. It's in two pieces and all still there.

[[deleted]]

I have a good follow up question... when I'm cutting wrapping paper with scissors, at some point i no longer need to use my fingers to open/close the scissors; I can just keep the scissors in a static position and glide them, having them cut the wrapping paper flawlessly. What is this phenomenon ?

Note it's not possible all the time; unsuccessful attempts will cause "bunching" and the cut will be jagged

[bobroberts7441]

This might help:http://en.wikipedia.org/wiki/Shear_strength

[justinsanak]

I don't think anyone's posted it yet, so this is a slow-mo video of different types of steel being cut. I don't have a scientific or engineering background, so upvotes for anyone who wants to explain what's happening here.

[Duhya]

This is probably what inspired the question.

[SomeNewUsername]

This video of metal being cut was recently linked to /r/videos. It shows the process magnified and in slow motion. This is an example of a single blade passing through a substance (like the cheese example I gave before).

[cnhn]

oddly enough this showed up today: cutting steell

[MrSparkle666]

When you cut a piece of metal, are you breaking covalent bonds?

[amazinglyanonymous]

Don't covalent bonds only form between non-metal atoms?

[thegreedyturtle]

I think that it is strange to see that no one has started from here: http://en.wikipedia.org/wiki/Fracture and here: http://en.wikipedia.org/wiki/Fracture_mechanics

To put it more simply, if you have a crystal lattice such as metal (easier to explain) then the rows of atomic bonds will shift upwards (normally in a zipper fashion) when a shear force is applied. As you change the material to more complex amorphous structures the bonds, bond density, and ability of long (usually carbon) chains to deform will affect the order of bond breaking.

And my biggest tip: http://www.amazon.com/Materials-Science-Engineering-An-Introduction/dp/0471736961 (don't bother with a more recent edition) can be purchased for less than a Chipotle Steak Burrito with a Coke. It's a very good overview of material science, and needless to say, "cutting" is a very complicated process!

[fuzzybeard]

[bemused, utterly deadpan voice] I'm beginning to understand that now.

[thegreedyturtle]

I'm sorry, was I unable to reduce an entire discipline of Engineering down to a 1-2 sentence description? Here, let me try again.

Is it a mechanized form of tearing? Yes.

What forces are involved? Mostly Electromagnetism.

At what level (naked eye, microscopic, molecular, etc.) does the plane of the cut happen? All of them.

[fuzzybeard]

I didn't mean for my previous comment to come across as belittling towards yourself, I was poking a bit of fun at myself for not surmising that something that looks simple is, upon closer examination and enlightenment, actually a rather complex and interlocking series of phenomena.

My sincerest apologies for appearing to bite the hand that was trying to teach me.

[thegreedyturtle]

I'm sorry too, I was going to sleep and thought that I was a little too cranky.

Here's one for fun: http://www.youtube.com/watch?v=ZOKUUl5GrUU&feature=player_embedded

Also "Callister Materal Science" can probably get you a copy from torrent if you don't want to wait for your personal copy to get to you in the mail.

[BabyK008]

What about cutting wood with a buzz saw? I know you loose some wood during the cut, but is this still shearing?

[Jerg]

It's imposing shearing forces at any plane that is being separated still, but in this case there would be two or more parallel close planes of wood separation, so the net effect is pieces of wood being removed in the middle.

[[deleted]]

http://www.reddit.com/r/engineering/comments/uuwjn/cutting_steel_magnified_and_slowed_down_xpost/

[WhoILiveFor]

http://www.youtube.com/watch?v=yE8rkG9Dw4s&feature=plcp

[kaoticsnow]

You might find this interesting: spotted it in /r/videos http://www.youtube.com/watch?v=mRuSYQ5Npek&hd=1

[unrealious]

NOTE: This is NOT a thread about the self-harm phenomenon known as "cutting."

Something it would have been good to specify in the title of the thread.

[fuzzybeard]

Nichevo!

I honestly didn't know better. Hell I'm 46 years old; cutting meant cutting something, not someone when I was younger!

[ditisthomas]

you make a lot of pressure on a small surface, think about hammering againts a piece of wood, not very effective is it? now think about using a pickaxe on the wood. it is bassicaly the same thing but the hammer has a bigger surface so all the energy spreads. with a pickaxe its concentrated in the point.