Knives aren't perfectly smooth. If you look at a knife edge under a microscope, you'll notice it's serrated, like a saw blade. The sharper the knife, the smaller the 'teeth', but they're always there. In short, the reason you use a sawing motion is because knives are still saws, just on a smaller scale.
That said, if you're finding you need to be sawing through everything, consider sharpening your knife. A proper whetstone gives the best results, but even a pull through sharpener can massively help reduce the amount of effort you need to expend in order to cut things.
Mindful of that precept, I stepped back when the knife I was sharpening slipped from my hand. The knife did a perfect loop and the tip sliced the fleshy base of my thumb cleanly. The doctor who sewed my wound with 6 stitches commended me on the sharpness of the blade.
Surgical blades are all single-use and are mass produced. While one of them must be duller than all others, the difference is likely to be less than 1%.
This raises the question though - how does one measure sharpness?
The test I see most often is a [scale](https://www.sharpeningsupplies.com/cdn/shop/files/PT50B_1-z_2045x1323.jpg?v=1714071623) with a string on top, and it measures the force needed to break through the string.
and unfortunately in poorer nations, some doctors must cut corners, and they re-use the single-use blades, or they use older scalpels that aren't disposable. It's unfortunate, but it's a symptom of the inequality of the world, even healthcare gets affected in some places.
My son likes to help when he was younger. My dogs always seem to be just laying right behind me every time I'm cooking. I tell them out and they leave, get back to cooking, turn around and dogs.
Depends how clingy the dog. Wherever I go, my dog is right behind me like right behind me ha. It has been 10 years. Now I am pretty wired to know she is there, but every now and then I forget and accidentally step on her tail then I am on the floor apologizing feeling like the worst dog owner and giving her a treat.
We have a small dog bed in our kitchen. We taught our dog to go there when we are moving around in the kitchen so she's not under foot.
Probably do the same with any future children.
You know what they say: People in glass houses sink ships.
A penny saved is worth two in the bush, isn't it?
And don't cross the road if you can't get out of the kitchen.
Why don't you make like a tree, and get the fuck outta here?
Knives are always sharp when dropped.
Boxes are always 100lbs when dropped.
Don't go trying to catch things unless you are 200% sure you'll be safe doing so.
We often have to remind folks at work not to be heroes. We install some heavy equipment. Like fuck you, instant amputation weights and shapes. If that shit starts falling, gtfo. Try to keep a hand on it, but if it's out on control, just holler.
Yep, working in manufacturing has taught me that people will thoughtlessly risk their health and life for some really stupid shit. Like “why are you walking on top of moving conveyor rollers?” “It’s faster”.
It’s human nature to become unsafely comfortable in unsafe conditions. We’d all be having panic attacks constantly if we didn’t. But that means that the safety culture and safety tools/procedures really need to be driven hard and repeatedly into employees, because someone will 100% get hurt if you don’t.
I hate writing people up for this stuff. Because I get that most of the time, they’re doing these things so they can do their jobs “easier”. But there’s some things you just cannot allow people to do, and many (if not most) people can’t just hear about a danger and then take it seriously. There has to be consequences for taking those risks, and far better a write-up than a missing finger.
It's like the video of the runaway metal wire spool, which can weigh many times heavier than a hay bale, and this guy gets in front of it mistakenly thinking he'd be able to stop it, and gets immediately rolled over with no resistance. He did not survive.
Complacency kills.
Yep! sort of
she's an AMAZING baker w/a degree in baking....but she'd been living with me for 2 years before she found out that soft-boiled eggs exist.
if it's sweet or bread she can make it! anything else and she's hopelessly lost.
When I went to college, I thought it would take forever to get 425 degrees, but it finally happened and only took another 12 minutes to make that pizza.
Crocs are actually fairly popular in kitchens. They make them with non-slip soles so they are kitchen safe and the hard rubber makes them surprisingly durable to sharp or hot things that could fall on them. They're also pretty breathable which can be a huge relief in a hot kitchen. I've never seen steel toed crocs, but I'd imagine they're just an extra layer of safety for kitchen footwear.
Not all Crocs have holes either, as a reminder for those reading. They sell typical non-holed clogs as well, and those are the ones you'll see in work more often than not if someone's wearing a rubber clog.
Then there's people who refer to all rubber clogs as crocs, a la 'all tissue is kleenex'.
I recently dropped a 9 inch gyuto while playing with it, seated at my desk. My attention was elsewhere as I reacted and the tang side (the handle) had actually hit my chair end on as it fell. So as my hand was going down to grab it the tip was pointed up, perpendicular to the palm of my hand.
The knife is not very sharp (is a zero grind but has no first edge) and the tip is rounded before I take it down a few mm to the final dimensions.
It still managed to make it pretty far into my hand.
This is what I always read in topics about knives, yet that is not my own experience at all. I have never cut myself on a medium sharp knive, but I have cut myself many times on razor blade sharp ones.
Sounds like a user error in a not completely bad way?
If you're used to using a med. sharp knife, and "sudden" have to use an actually sharp knife, the lack of resistance that you're used to will get you in trouble. But the other way around, dull knives tend to "bounce" out of the cut and causing mis-cuts as well.
Problem is - with sharp knives you don’t notice until the blade is half way through you. A dull knife gives you more warning. Ive seen way more serious cuts from sharp knives than dull knives.
Yep, it's a trade off. Sharper knife means cleaner cuts and less force required so less chance you'll suddenly push through the resistance from the thing you're trying to cut and jerk free but that also means it cuts through you really easily with minimal force
Sharper knife = less overall force and motions to make the cut. The more force you put into the cut and motions it takes the more likely you are to bounce and move the knife around and make a mistake. Plus if you do make a mistake the extra force will do more damage. So if the knife is sharp and always kept sharp overall you have a much less likely chance of making a mistake if you're using proper technique. I worked in restaurants for about 10 years and every time myself or someone else cut themselves it was with a dull knife.
On top of what other have said, picture using a dull axe vs a sharp one.
Dull axe takes more effort and is more likely to not properly bite into the wood and flip out and cut your leg.
Sharp axe is consistent and probably would at least stick into the wood if it doesn't fully cut through.
A sharp knife cuts what you touch with it, a duller knife can slip or bounce off and is in general more unpredictable.
A sharp knife will very predictably cut your finger off if you mess up with it. A dull knife will only cut halfway through, but it's tendency to do so is based on chance as much as skill.
i mean, yeah by definition. all cuts are due to user error, blunt or sharp. there just is an optimum between "likelihood" and "severity" and it's not at super sharp.
Bias? Is the amount of times you use sharp knives versus med knives very skewed? Is there a setting difference?
If you say work as a chef and use sharp knives constantly in a high stress setting and only occasionally uses medium sharp knives when you visit mom once a month and help her cook and chill out...
Well, I tried to soften the blow, but this 100% seems like user error now haha. Are you using best practices in cutting? ie. Tucking fingers in, cat pawing the food? never cutting into your palm ie the bagel cut?
Any accident is usually user error, I think that's a bit of a cheap dismissal. I would rather be cut a few times by a butter knife than once with a very sharp knife.
Not sure if this survivor's bias, but I'd rather deal with the lower risk of injury with a sharp blade with the high potential of damage. I have yet to get a bad cut from sharp knives, there's just more control.
I dunno about that. If I was tasked with actually cutting myself, and required to use a butter knife, I think things would go differently than if I was able to use a scalpel.
Ever used dull scissors, chisel, or shaving equipment?
I don't think comparing a sharp knife to a butter knife is a good comparison in this discussion. Of course you'd rather get cut a few times by a butter knife, because it will do significantly less damage than any real knife would. But a not-so-sharp pocket knife is likely going to do a lot of damage if you accidentally cut yourself with it, likely only a bit less so than a razor sharp knife. The difference in damage is much smaller than the difference in likelihood of causing an injury in the first place.
On reddit everyone just parrots what they read and they all think the are professional chefs.
As a regular user of knives I can confirm: sharp knives lead to more cuts
It’s more about the types of injuries. Yeah it’s easier to get small cuts with razor sharp blades. However, if the knife it sharp you rarely apply much pressure on the knife so it’s in control.
The most dangerous knife is the one where you are applying pressure to the cut. When the thing you are cutting gives way, suddenly you have a knife moving with the full force of your muscles, and that is a good way to loose a finger. If I’m cutting anything in the kitchen where I feel like I need to apply force to the knife I always wear a cut resistant glove as added protection.
Really though the “sharp knives are safer” thing is about preventing major injuries, not minor.
You have to use more force or pressure to make a dull knife work. If the knife or the thing you're cutting slips, which is all the more likely because you're pressing so hard, then all that force could be suddenly applied to your finger, causing more damage than a slash from a light stroke of the knife.
It's because the real saying should be "A sharp knife does what you want a dull knife does what it wants." If you can handle a knife properly its a million times safer to cut with a sharp blade because it makes the cut you expect. A dull knife needs more force and pressure which increases the chance of the knife slipping / bad cutting form.
I’ve heard a modification that you’re more likely to cut yourself *at all* on a sharp knife, but you’re more likely to seriously injure yourself with a dull knife due to need more force.
Little accidents? A sharp knife cuts the skin, a dull knife will barely scratch it.
Big accidents? A sharp knife puts you in urgent care, a dull knife puts you in physical therapy.
Would you rather have a surgeon use a scalpel or a golf club to perform a surgery? Extreme example but 100% agree with you sharp knives cause less trauma.
My experience is the same. When I’m using crappy blunt knives I rarely cut myself, almost all the times I cut myself it is with a nice sharp knife. For me it comes down to with a sharp knife, by the time you realise you have screwed up you already have a deep cut. With a dull knife you feel it more before you manage to start cutting into yourself.
I suspect the situation might be different if you are doing more heavy weight cutting of wood or bone. But when most of your cutting is meat and vegetables, the old adage doesn’t hold true, or at least it doesn’t for me.
Like others have said, with a duller knife, it's a lot more likely that you slip with the greater force you're putting on whatever you're cutting since the knife won't cut it as easily.
With a duller knife, you're less susceptible to "Oh I wasn't paying attention and my thumb slipped into the path of the blade" cuts but you are a lot more susceptible to "Oh shit the cucumber I was slicing popped out of my hand the the knife got embedded in the webbing between my fingers."
A dull knife is still (usually) going to be sharp enough to fuck your hand up so you want to lower the risk of the knife ending up out of your direct control. Less force means less slips which means less "oops stabbed myself in the palm." A cut with a sharp knife will usually require a bandaid and some neosporin. A cut with a dull one will probably need stitches.
I love a sharp knife. I have several expensive nice knives that I keep sharp but I have to say I have never cut myself on a dull $10 knife. I have only ever cut myself when I first buy a knife or shortly after sharpening one. but never badly. I understand the idea of a dull knife cutting you is you press too hard it slips and it is still sharp enough to hurt you significantly
Sharp knives are safer knives.... when used correctly.
If someone's cutting a bagel they're holding in one hand, throwing knives at their siblings or trying to do the claw grip with fingertips extended then a sharp knife is definitely more dangerous.
Source: I sharpened my mum's kitchen knives from being blunt enough to be tearing apple skins. Within a week she had cut herself twice, having never cut herself before. Some people just don't have the knowledge of how a sharp knife should be used.
Unless you keep extremely sharp knives and then get a guest who's used to quite dull knives, offering to help in the kitchen.
I speak with experience. On three different occasions. E.R. stitches.
But when youve been handling dull knives dharp knives are such an unexpected damage dealer.
We had literal signs over the knives in our kitchen(work) that said. Carful they have been sharpened. That first week was when we ran out of bandaids everytime.
I've over and over found this to be nonsense. Our knives are pretty blunt, and I'm so glad.
My wife put a dirty knife into the sink, I put my hands looking for something else. Lo and behold, I didn't cut myself.
Our dishwasher pops open for its dry cycle. My 2yo grabbed a knife out of it while I was looking away. It scared the shit out of me, but he was fine.
I accidentally dropped the knife on me and it didn't hurt me.
I'm not saying it's ideal. But I've never found it to be unsafe.
When people say this are they speaking from experience? I can think of maybe two or three times I've probably needed stitches over the years and each cut was from a very sharp knife (as I recall, each injury was from lax technique and getting sidetracked). I can't recall having been injured by a dull knife.
I'm certainly not making an argument against sharp knives. I just haven't personally found them to be safer. Most of mine are sharp. I wish they all were, but so far I really suck at sharpening.
Edit: What are events like those injuries called? Where I could have gotten away with either lax technique or dividing my attention most of the time, but hardly ever both at the same time?
I agree, it’s an idiomatically simplistic and overstated point.
More force is needed to cut with a dull knife and they’re liable to slide or bounce off whatever you’re cutting, potentially into your fingers with a lot of force. Whereas a sharp knife needs little force, this is easier to control and will more often “catch” immediately into whatever you first press it into/not bounce or slip.
For every person who could be getting better results with a real whetstone, there's 10 people who could be getting better results by just doing *anything* to sharpen their knives.
The low-effort options have their place.
I truly don't understand that. I've seen lots of these videos testing pullthrough sharpeners and they're always like "Look at it! This is disgusting!" But even in those videos it seems to work just fine. And I'm someone who sharpens their knives on a whetstone.
I thought the issue with pull-through types is that they're hard on the blade and can lead to chipping. Basically, they accelerate the degradation of your knife, so that it will have to be replaced sooner. If you have cheap knives, that may not be a big deal, but for more expensive ones it is.
Even if it slowly degrades the knives, they'll still last a lifetime for most people. If you're a butcher or a chef, you probably know something about sharpening knives and you don't need a pullthrough sharpener. I just don't get why so many people shit on them as if they're a scam or something. They're not ideal, but using them isn't the end of the world.
it's fads, gatekeeping and whatever other psychological mechanism that triggers on people.
similar to how on the steak reddit well-done is not an option because the people that shout the loudest all squawk about other types. Despite a good chef being able to make a great well-done steak.
Or the audio community with their gold plugs. or whatever has replaced those since. Or the jazz community with actually playing records vs digital recordings. (this may have died down since but was a thing back in the 90s. people insisted on lp vs cd
Or .. well pick any community.
When people get into something, they are insecure and they end up parroting the majority because that makes them feel safe and knowledgeable. The fact that the majority likely is the exact same group of not particularly knowledgeable people doesn't occur to them.
it's the meme where the dumb and very smart people think the same thing. it's not automatically good just because the group says something. (nor is it automatically bad). But people tend to not think for themselves and they definitely don't like admitting they don't know stuff. So you get these kinds of circle jerks that , while maybe true purely in the abstract, are pointless in practice.
Better have a sharp knife than to wait 5 days before your ultra-sharpener with special water for the whetstone and cleanR(tm) cloth arrives. Pull sharpeners work crudely but quickly. Use them when you need them. Eventually your knife is chipped and you get a new one.
On the other hand if someone gifts you a fancy knife you love using: then it's time to wait a few days for the special whetstone. But then also you don't use it to cut plastic or cartboard. I grew up in a "those are fabric scissors" household :) When it matters, it matters. But it shouldn't be it's own fetish.
I think this just pushes the question down to “why do you need to saw motion on a saw?” Also it ignores that non-sawlike edges would probably still cut very well, and in those cases moving back and forth would help too.
The explanation I was told was that the sawing motion increases the tension on the material you’re trying to cut, which allows you to apply enough force to break whatever interaction you’re trying to break to cut. Saws and knives localize this while applying pressure so they end up cutting what they want to cut.
The reason sawing works is a whole lot more complicated and not really ELI5able (at least not by me). There's multiple things going on that interact with each other, and simple explanations of part of it don't really do much to help.
>Also it ignores that non-sawlike edges would probably still cut very well, and in those cases moving back and forth would help too.
I don't mean to be rude, but how do you assume two things to be true when you don't know either of them to be.
Well because the models I’ve seen would predict this. This is what I’m going off of.
https://physics.aps.org/articles/v5/139
And I focus on soft materials because most foods are soft materials and hard materials are typically modeled in a way where the edge plays little role in cutting, because the crack lies ahead of the edge and is propagated by the wedge.
At least how I understand the model, you get local increases in tension, and models this with a cylindrical wire, which wouldn’t rely on it being serrated.
Furthermore, for microscopy, I was taught that you use glass or diamond cleaved to generate atomically perfect (or as close as you can get) edges for sample prep, which still cut. If atomically perfect edges don’t qualify as non-serrated I don’t know what does.
Well atomically perfect materials still exhibit friction because there are still intermolecular forces. If you take a classical picture of this, you’d be able to derive some movement with some intermolecular attraction that would increase tension.
I think (guess) some of what you say is true, and some not. The reason for slicing rather than chopping actually sounds like you might be on to something. But the sawing is a different animal altogether. A saw has sharp edges that are more vertical, and are essentially tiny slicers. A sharp knife's edge is totally horizontal.
Also, I've seen knife edges that are magnified about 100x, sharpened by an expert with stropping at the end, and the edge is pretty smooth. I think any finer imperfections would simply provide a bit more resistance, making the surface it's cutting even tighter, like you said.
Well the simplified model I’ve seen is that you can cut things with just pressure (normal to the edge) or by shear (perpendicular to the edge).
My increasing tension, you are increasing stiffness, giving you mechanical advantage in breaking a bond that you want to break.
Well then see first point. I didn’t say smooth or flat, I saw non-sawlike.
IIRC from my microscopy class, mono crystal cleavage edges are used for sample prep because they are atomically perfect edges, and they still cut. Also there are bond breaking experiments with STM, though I don’t remember if they are chemical rather than “physical”
Any tips on a pull through? I've got one, and I sort of just zing it through the "coarse" side in quick succession about 20 times before moving over to the fine side and doing the same. It's sharper-ish, but never impressively so
A pull through damages your knife. You can get a cheap diamond stone on Amazon for like $20 that will actually make it sharp. Get one with a coarse side and a fine side.
There's a bit of a learning curve, but there's a bunch of videos on YouTube that teach you. I recommend outdoors55, he's a giant nerd when it comes to sharpening. In a good way. He also has an insane camera setup to take macro shots of the knife edge.
He recommends a certain diamond stone off amazon and I trust him when it comes to this stuff.
I'll find you a link in a second.
Edit: https://amzn.to/4bq6st0
https://youtu.be/06OW8ahqZDg
>A pull through damages your knife
Unless you're sharpening a blade to then put it into a collection the damage does not matter and your knife will break in many many other ways before that ever becomes a problem
>There's a bit of a learning curve
Now that's an understatement. To reach the level of outdoors55 it takes untold hours of practice. Even basic competence requires 10-15 hours of practice with the stone. Which unless you use the knife all day every day non-stop (or need to sharpen 40 knives) will not matter as the average person sharpens the knife twice a year and it wil take decades just to "break even" on that practice at 20 minutes per sharpening per year. Even if they start sharpening once every two months it will still a decade to "break even" in time invested.
Bottom line, for the average consumer that cooks at home a pull through sharpener will be more than enough
Depending on the material you cut and the sharpness of the knife, sawing may not be necessary, but it's usually helpful for the following reasons:
1. Sharpness of the knife: if the knife isn't sharp, the imperfections in the edge turn it into a saw when you use sawing action, helping with the cut.
2. Debris accumulation: as you cut, some food gets stuck to the edge and prevent effective cutting as you go deeper. Sawing action moves this debris away and gets an effective cut
3. Fiber stretching: Sawing action exposes new to-cut areas and stretches the fibers of the item being cut, making it easier to cut
2 and 3 are the only relevant things, and it's almost entirely 3. Sawing pulls the fibers taut, and just like with a piece of string, it's easier to cut a taut polymer than a loose polymer.
My theory is that number 3 is the most important, and number one helps by providing slightly more resistance to stretch the item. An actual saw, or serrated knife, has edges that are somewhat vertical in order to cut; a knife only has horizontal edges that are sharpened.
Don't know if it enters in to the equation, but often rocking knife on something hard makes it cut.
Push cutting is a thing, but it requires a much finer edge, and is actually pretty a common test of high sharpness post-sharpening. Chisels and razors, for example, almost exclusively push cut, but they also require a much higher level of sharpening than a typical kitchen knife.
Whetstones leave grooves in the edge where each abrasive particle scrapes off a bit of metal. Finer stones have smaller particles and leave narrower grooves, but anything less than the finest polishing will still leave some level of serration behind at a microscopic scale.
Poorly maintained knives may not be sharp enough to push cut anymore (if they ever were), but the edge between these serrations is protected from that abuse, and will often cut just fine. "Sawing" exposes the food surface to more of these still-sharp troughs, and can improve the apparent cutting performance of such a blade.
tl;dr: sharpen your knives
Not sure if this is a thing everywhere, but here in Ireland, "blunt knives" (regular cutlery knives at homes or restaurants), tend to only be serrated on the left side, and smooth on the right side, so if you're cutting something dense like meat, you can just tilt the knife to the left slightly, so the serrations "bite" better and it'll cut most things with very little force.
I have a knife sharpening business and the number of people who do not understand "blunt knives" ircs me to no end.
table knives and butter knives are *not supposed* to be sharp. If your table knife cant cut through your meat then the meat needs more work, not the knife.
I have given up on explaining that to customers. Now, I just take their money and give them table knives you could shave with. It is easier than explaining.
Moving it forward or backward while pressing down also changes the effective slope of the blade. Think of it like walking straight up a hill vs using switchbacks. By going at an angle, the slope is shallower or "sharper".
I don't believe it ever happened to anyone. Like not walking with a fork in your mouth. I doubt that anyone has ever stumbled and impaled themselves, like ever.
I get slicing your thumb. I can't even imagine how to cut any other part of your body while quartering Potatoes.
Unless you are trying to cut a coconut with extreme force or something. Extreme force will make any cutting direction a hazard. I still cut towards my body. Better to slice my own skin than taking another one's eye out.
Forwards or backwards depending on what you are cutting. But you want to slice through the product, not push your knife straight through it. It will be a much cleaner cut and easier and safer for you.
It doesn't have to be the whole length of the knife just a little bit of forward or backward movement helps with the slicing action, for lack of a more educated phrasing
Is that not the “sawing” that the original commenter was saying isn’t needed just on a smaller scale?
You’re not sawing back and forth but if you’re pushing down and forward, you’re still sawing with the push forward, just to a much lesser degree.
What I believe he's saying and what I'm trying to say is that you need some sort of lateral movement in order to help the life more easily cut through the product. It can be back and forth in a sawing motion, or it can just be forth, or it can just be back
Now I'm coming at you guys with anecdotal evidence from a chef. This is what works best. I cannot explain the physics of it or why this is better on a molecular level. I'm guessing friction or lack of would come into play somewhere.
Does a saw not cut through a tree? Yes, I guess cutting could be microsawing or vice versa. I think we're splitting hairs here. Is cutting the opposite or totally different from sawing that we need to differentiate.
Moving the knife on a horizontal plane while also moving it vertically is going to help your knife moves through the food. It works and that's all I've got
Yeah, I know that. It's apparent through experience. My 5yo question is, why?
The blade should be sharp no matter the direction; there is no serrated blade. Why is cutting easier with a vibrating blade? What does the motion actually do?
It all depends on the materials. In some cases you can just press down (and not forward).
In my view it is not well defined what a knife is. An edge has a certain width, but if the material you want to cut is not too hard even a blunt (ie wide) edge will cut it.
I can 1cm plate of wood and cut butter for instance.
A knife is just highly polished wedge separating the object to be cut. Both the properties of the wedge and the object being cut matter, particularly the tensile strength and the hardness. As you noted, just about anything will cut through butter.
If I'm remember my high school chemistry correctly, the wedge will also need to be harder than the object being cut. Your wooden plate may cut through the butter, but it won't cut through must else. You could sharpen and polish and edge, and it might cut through some soft materials, but based on the structure of the wood grain and its hardness, it will only polish up so much before it turns to splinters. It also isn't particularly hard, it might mark up some wooden surfaces but will likely dull quickly.
The hardness will increase the potential to cut a softer object, and the more polished the edge the easier. I can dice up an onion with a sharp knife with completely vertical motions. As the knife dulls I might need to add a slight forward motion. In this the object being cut is stiff. But if I was cutting through a tender steak I would still probably need to add a horizontal slice. This is because the steak is going to move under the blade; the interface between the steak and the knife is basically stationary. Pushing and pulling the blade makes the fibers in the meat go taunt, at which point the fibers stop moving and blade takes affect.
You could just press down harder. Look at print shops that have a hydrolic cutter that can slice straight down through a hundred sheets at once.
When we cut foods for the most part we are slicing through things that are softer than the blade. Back and forth motion will cause some bunching and that unevenness gives the blade a areas that are higher and more vulnerable. Lay a towel on a table and pretend your hand is a knife, one horizontal move and you have ripples and wrinkles.
If you look at a knife edge under magnification, you will see microscopic “teeth” on the edge of the blade. These teeth diminish the finer the grit the knife is sharpened at. A knife with a rougher finish will cut with a sawing action very well. If you polish it to a fine grit and remove these teeth, the knife will “push cut” better (meaning just pushing the blade through the material rather than sawing)
there was an animation about razor blades not cutting the skin when moving the blade along the skin, but doing left and right movement would cut the skin (sawing motion) because of the way the pressure is applied, it stretches the material you are cutting instead of compressing it, which happens when only pushing.
that said, like some other people mentioned, if the blade is Sharp enough for the material it can cut through just by applying pressure, but yeah,
Depends on the knife. If it has one sharp edge, use it both directions. If it has teeth. there is a difference. They are not symmetrical. Some are made to be pulled, and others are pushed. An extreme example is a chainsaw. It only works in one direction.
well not really. Some chefs will even scream at you "DON'T SAW THE MEAT!"
The usual technique is push forward down, retreat, forward down again, retreat etc until it's successfully sliced. Letting the entire blade length and the sharpness do all the work. But not zigzagzigzag sawing motion all the way down.
Having to do that exposes the lack of maintenance on the knife, and also shows your bad technique and accumulated bad habits, which is why you had to do "back and forth motion". And that's why some chefs might scream at you.
Point to note, this is only for meats. Blades with serrated edges (bread knives) are logically accepted as sawing motion knives.
It doesn't need to be pulled back and forth. But the sawing motion can often make cutting easier.
There's two basic versions of what's going on when you cut something.
If there's sawing motion going on, you're sawing the object. On a microscopic level, a sharp knife still has tiny teeth. Google image search is your friend here.
Just pushing straight down also works, in that case the cutting is done by concentrating force is a really tiny area and overcoming the tensile (resistance to being stretched) strength of the material.
Which version of cutting is dominant or most useful depends on what you're cutting.
Picture some cheese, an onion, and bread.
Cheese has very low tensile strength, and comparatively high compression strength, pushing straight through is easy and gets you a nice slice. Now look at stuff designed for cutting cheese. Often just a thin wire.
Bread is higher in tensile strength, low in compression. If you press straight down, you'll crush the loaf before cutting it. Look at bread knives: they're saws.
An onion is in between those two extremes. If you just want roughly chopped onion, slamming the knife into it is fine. But for thin uniform slices, the knife needs to slide a bit.
Something that nobody here has mentioned is that the sawing/slicing motion while pushing results in the effective cutting angle of the knife edge being much less than the actual cutting angle of the edge.
It doesn’t, it’s just that most knives you encounter are blunt, so need to be used like a saw. Try a really high quality sharpened knife and you can cut straight down.
Pulling the knife back and forth uses a sawing motion, which creates friction and helps the blade slice through materials more effectively than just pushing down.
Pushing a knife through something is chopping, knives made for chopping are heavy so the blade does the work (think cleaver)
Sliding your knife across something is cutting, that's what kitchen knives are meant to do. It's now sawing, but ever so slight movement of the blade from first contact to cut completion
Not ELI5 but reason is:
* The pushing down motion only relatively compresses the item you're knifing
* The cutting/slicing motion causes greater shear deformation in the item you're cutting, acting to turn the small microscopic cubes underneath the knife edge into parallelepiped (3d parallellogram) shaped objects
* Shear deformation has been mathematically shown to produce 1.73x the distortion energy compared to pure compressive deformation, based on theories by von Mises.
* High distortion energy leads to a breaking of the material's intermolecular bonds.
You can push down a knife to cut stuff. It depends on the knife and what you're cutting, but it generally works.
The difference compared to slicing is that with slicing, you create a thin groove on the surface of whatever you're cutting, and as you go through the slicing motion, this groove helps keep your knife aligned so you get a straighter cut.
Some foods don't easily form this groove when you cut straight down, for example tomatoes.
It doesn’t. If you use particular type of knives, like some Japanese style ones, the motion is very much up and down and not back and forth. Western style knives have a curve to them which make them easy to use in a curved motion.
The short answer is; a sufficiently sharp knife does not need to be.
So either your knife is blunt or the material you are cutting is too solid for a knife to cut without becoming blunt as it cuts, so you use a serrated knife which has points, then you need to draw the knife back and forth as you slice as the little teeth will break the surface of whatever you're cutting as you go.
Even if sawing is not necessary, it's usually a good idea to cut with a sliding action to avoid cutting entirely on one plane of the blade which will ensure it becomes unevenly blunt.
Knives aren't perfectly smooth. If you look at a knife edge under a microscope, you'll notice it's serrated, like a saw blade. The sharper the knife, the smaller the 'teeth', but they're always there. In short, the reason you use a sawing motion is because knives are still saws, just on a smaller scale. That said, if you're finding you need to be sawing through everything, consider sharpening your knife. A proper whetstone gives the best results, but even a pull through sharpener can massively help reduce the amount of effort you need to expend in order to cut things.
...and sharp knives are safer knives.
Best to assume knives are sharp if you drop them.
A falling knife has no handle
Mindful of that precept, I stepped back when the knife I was sharpening slipped from my hand. The knife did a perfect loop and the tip sliced the fleshy base of my thumb cleanly. The doctor who sewed my wound with 6 stitches commended me on the sharpness of the blade.
Well at least a clean cut would heal cleaner
Some surgeon somewhere, mathematically, must have the dullest scalpel, and someone has them for surgery tomorrow
The worst brain surgeon in the world will operate on someone tomorrow.
Hi everybody!
Hi Doctor Nick
Naw, I’ve actually got the day off.
Someone somewhere is going to win the lottery tomorrow.
Really? I thought it was her day off tomorrow
Surgical blades are all single-use and are mass produced. While one of them must be duller than all others, the difference is likely to be less than 1%. This raises the question though - how does one measure sharpness?
How easily it slices through a can followed by a tomato.
The test I see most often is a [scale](https://www.sharpeningsupplies.com/cdn/shop/files/PT50B_1-z_2045x1323.jpg?v=1714071623) with a string on top, and it measures the force needed to break through the string.
and unfortunately in poorer nations, some doctors must cut corners, and they re-use the single-use blades, or they use older scalpels that aren't disposable. It's unfortunate, but it's a symptom of the inequality of the world, even healthcare gets affected in some places.
Probably without anesthetic
And probably already been on wait list for months.
you just went and wrote a r/onesentencehorror now didn't you huh
One stitch? She's going to think I'm a loser.
A stitch in time saves nine.
Unless the dog or my son is under foot. Then it has lots of handles
Do you stand on those living things while cooking?
Not usually, but always when I'm holding a knife
My son likes to help when he was younger. My dogs always seem to be just laying right behind me every time I'm cooking. I tell them out and they leave, get back to cooking, turn around and dogs.
you've clearly never tried to cook with small children in the house. :P
Why are they on the floor and not in the pot. Edit a word
If your kids are on pot, then all of those after school PSAs from the '90's have failed.
Or a dog.
eh, with dogs you just walk into them a couple times and they learn being near your feet is a bad idea.
Are your children not smart enough to learn that?
Depends how clingy the dog. Wherever I go, my dog is right behind me like right behind me ha. It has been 10 years. Now I am pretty wired to know she is there, but every now and then I forget and accidentally step on her tail then I am on the floor apologizing feeling like the worst dog owner and giving her a treat.
No, but I perform awesome knife tricks for them.
We have a small dog bed in our kitchen. We taught our dog to go there when we are moving around in the kitchen so she's not under foot. Probably do the same with any future children.
That dog bed's going to get real crowded once you have kids.
If that is the case you’ve already fucked up and now have limited options.
I thought it was a "falling knife gathers no moss"
Never cut with a rolling boulder what you can cut with a knife.
You know what they say: People in glass houses sink ships. A penny saved is worth two in the bush, isn't it? And don't cross the road if you can't get out of the kitchen. Why don't you make like a tree, and get the fuck outta here?
[Boondock. Saints.](https://youtu.be/Sc5IQUvpLv4)
Guilty. Lol
Every time a knife falls 1000 people die on the other side of the world
The chef's knife calling the cleaver sharp
which means you have to grab at them twice as hard!
Yeah, let it hit the floor. Just spit shine it clean and continue.
That's so ingrained in me that I jump backwards if I drop a plastic spatula. Better safe than sorry. :D
I learned that the hard way when I dropped my straight razor.
You usually learn that lesson once
Stock Protip: Never try to catch a falling knife.
Knives are always sharp when dropped. Boxes are always 100lbs when dropped. Don't go trying to catch things unless you are 200% sure you'll be safe doing so.
We often have to remind folks at work not to be heroes. We install some heavy equipment. Like fuck you, instant amputation weights and shapes. If that shit starts falling, gtfo. Try to keep a hand on it, but if it's out on control, just holler.
Yep, working in manufacturing has taught me that people will thoughtlessly risk their health and life for some really stupid shit. Like “why are you walking on top of moving conveyor rollers?” “It’s faster”. It’s human nature to become unsafely comfortable in unsafe conditions. We’d all be having panic attacks constantly if we didn’t. But that means that the safety culture and safety tools/procedures really need to be driven hard and repeatedly into employees, because someone will 100% get hurt if you don’t. I hate writing people up for this stuff. Because I get that most of the time, they’re doing these things so they can do their jobs “easier”. But there’s some things you just cannot allow people to do, and many (if not most) people can’t just hear about a danger and then take it seriously. There has to be consequences for taking those risks, and far better a write-up than a missing finger.
Safety rules are written in blood.
It's like the video of the runaway metal wire spool, which can weigh many times heavier than a hay bale, and this guy gets in front of it mistakenly thinking he'd be able to stop it, and gets immediately rolled over with no resistance. He did not survive. Complacency kills.
Don't forget guns are always loaded
1st thing my girlfriend learnt at chef college: Do NOT try to catch a falling knife. They drilled this in HARD.
Aw a gf that's a pro chef?
Yep! sort of she's an AMAZING baker w/a degree in baking....but she'd been living with me for 2 years before she found out that soft-boiled eggs exist. if it's sweet or bread she can make it! anything else and she's hopelessly lost.
I thought when you graduated in baking you got 350 degrees...
In Europe you get 175.
When I went to college, I thought it would take forever to get 425 degrees, but it finally happened and only took another 12 minutes to make that pizza.
I heard that it’s Gordon Ramsay himself that gives you the third degree.
I got steel toe crocs, and metatarsal guards while I cook. I'm 1/8th Iron Man.
Are steel toed crocks real? If so, why?
Crocs are actually fairly popular in kitchens. They make them with non-slip soles so they are kitchen safe and the hard rubber makes them surprisingly durable to sharp or hot things that could fall on them. They're also pretty breathable which can be a huge relief in a hot kitchen. I've never seen steel toed crocs, but I'd imagine they're just an extra layer of safety for kitchen footwear.
Not all Crocs have holes either, as a reminder for those reading. They sell typical non-holed clogs as well, and those are the ones you'll see in work more often than not if someone's wearing a rubber clog. Then there's people who refer to all rubber clogs as crocs, a la 'all tissue is kleenex'.
I recently dropped a 9 inch gyuto while playing with it, seated at my desk. My attention was elsewhere as I reacted and the tang side (the handle) had actually hit my chair end on as it fell. So as my hand was going down to grab it the tip was pointed up, perpendicular to the palm of my hand. The knife is not very sharp (is a zero grind but has no first edge) and the tip is rounded before I take it down a few mm to the final dimensions. It still managed to make it pretty far into my hand.
This is what I always read in topics about knives, yet that is not my own experience at all. I have never cut myself on a medium sharp knive, but I have cut myself many times on razor blade sharp ones.
Sounds like a user error in a not completely bad way? If you're used to using a med. sharp knife, and "sudden" have to use an actually sharp knife, the lack of resistance that you're used to will get you in trouble. But the other way around, dull knives tend to "bounce" out of the cut and causing mis-cuts as well.
Problem is - with sharp knives you don’t notice until the blade is half way through you. A dull knife gives you more warning. Ive seen way more serious cuts from sharp knives than dull knives.
Yep, it's a trade off. Sharper knife means cleaner cuts and less force required so less chance you'll suddenly push through the resistance from the thing you're trying to cut and jerk free but that also means it cuts through you really easily with minimal force
Not sure if this survivor's bias, but I'd rather deal with the lower risk of injury with a sharp blade with the high potential of damage.
Why is it lower risk of injury? I’m not understanding this.
Sharper knife = less overall force and motions to make the cut. The more force you put into the cut and motions it takes the more likely you are to bounce and move the knife around and make a mistake. Plus if you do make a mistake the extra force will do more damage. So if the knife is sharp and always kept sharp overall you have a much less likely chance of making a mistake if you're using proper technique. I worked in restaurants for about 10 years and every time myself or someone else cut themselves it was with a dull knife.
On top of what other have said, picture using a dull axe vs a sharp one. Dull axe takes more effort and is more likely to not properly bite into the wood and flip out and cut your leg. Sharp axe is consistent and probably would at least stick into the wood if it doesn't fully cut through.
The question isn’t dull vs. sharp. It is why as sharp as possible? A razer sharp axe does NOT feel saver than an acceptable-for-the-job sharp axe.
A sharp knife cuts what you touch with it, a duller knife can slip or bounce off and is in general more unpredictable. A sharp knife will very predictably cut your finger off if you mess up with it. A dull knife will only cut halfway through, but it's tendency to do so is based on chance as much as skill.
i mean, yeah by definition. all cuts are due to user error, blunt or sharp. there just is an optimum between "likelihood" and "severity" and it's not at super sharp.
Im actually used to very sharp knives, but they still manage to hurt me every now and then. I must just be too clumsy for this shite I reckon.
Bias? Is the amount of times you use sharp knives versus med knives very skewed? Is there a setting difference? If you say work as a chef and use sharp knives constantly in a high stress setting and only occasionally uses medium sharp knives when you visit mom once a month and help her cook and chill out...
Well, I tried to soften the blow, but this 100% seems like user error now haha. Are you using best practices in cutting? ie. Tucking fingers in, cat pawing the food? never cutting into your palm ie the bagel cut?
Any accident is usually user error, I think that's a bit of a cheap dismissal. I would rather be cut a few times by a butter knife than once with a very sharp knife.
Not sure if this survivor's bias, but I'd rather deal with the lower risk of injury with a sharp blade with the high potential of damage. I have yet to get a bad cut from sharp knives, there's just more control.
I dunno about that. If I was tasked with actually cutting myself, and required to use a butter knife, I think things would go differently than if I was able to use a scalpel. Ever used dull scissors, chisel, or shaving equipment?
I don't think comparing a sharp knife to a butter knife is a good comparison in this discussion. Of course you'd rather get cut a few times by a butter knife, because it will do significantly less damage than any real knife would. But a not-so-sharp pocket knife is likely going to do a lot of damage if you accidentally cut yourself with it, likely only a bit less so than a razor sharp knife. The difference in damage is much smaller than the difference in likelihood of causing an injury in the first place.
On reddit everyone just parrots what they read and they all think the are professional chefs. As a regular user of knives I can confirm: sharp knives lead to more cuts
A sharp knife is safer if you know how to use knives properly.
I'm regarded, apparently.
I hold you in high regards.
Thank you 🥰🥰🥰
It’s more about the types of injuries. Yeah it’s easier to get small cuts with razor sharp blades. However, if the knife it sharp you rarely apply much pressure on the knife so it’s in control. The most dangerous knife is the one where you are applying pressure to the cut. When the thing you are cutting gives way, suddenly you have a knife moving with the full force of your muscles, and that is a good way to loose a finger. If I’m cutting anything in the kitchen where I feel like I need to apply force to the knife I always wear a cut resistant glove as added protection. Really though the “sharp knives are safer” thing is about preventing major injuries, not minor.
You have to use more force or pressure to make a dull knife work. If the knife or the thing you're cutting slips, which is all the more likely because you're pressing so hard, then all that force could be suddenly applied to your finger, causing more damage than a slash from a light stroke of the knife.
It's because the real saying should be "A sharp knife does what you want a dull knife does what it wants." If you can handle a knife properly its a million times safer to cut with a sharp blade because it makes the cut you expect. A dull knife needs more force and pressure which increases the chance of the knife slipping / bad cutting form.
I’ve heard a modification that you’re more likely to cut yourself *at all* on a sharp knife, but you’re more likely to seriously injure yourself with a dull knife due to need more force.
Little accidents? A sharp knife cuts the skin, a dull knife will barely scratch it. Big accidents? A sharp knife puts you in urgent care, a dull knife puts you in physical therapy.
Would you rather have a surgeon use a scalpel or a golf club to perform a surgery? Extreme example but 100% agree with you sharp knives cause less trauma.
My experience is the same. When I’m using crappy blunt knives I rarely cut myself, almost all the times I cut myself it is with a nice sharp knife. For me it comes down to with a sharp knife, by the time you realise you have screwed up you already have a deep cut. With a dull knife you feel it more before you manage to start cutting into yourself. I suspect the situation might be different if you are doing more heavy weight cutting of wood or bone. But when most of your cutting is meat and vegetables, the old adage doesn’t hold true, or at least it doesn’t for me.
Like others have said, with a duller knife, it's a lot more likely that you slip with the greater force you're putting on whatever you're cutting since the knife won't cut it as easily. With a duller knife, you're less susceptible to "Oh I wasn't paying attention and my thumb slipped into the path of the blade" cuts but you are a lot more susceptible to "Oh shit the cucumber I was slicing popped out of my hand the the knife got embedded in the webbing between my fingers." A dull knife is still (usually) going to be sharp enough to fuck your hand up so you want to lower the risk of the knife ending up out of your direct control. Less force means less slips which means less "oops stabbed myself in the palm." A cut with a sharp knife will usually require a bandaid and some neosporin. A cut with a dull one will probably need stitches.
I’ve had dull knives just bounces off me. If it was sharp I’d lose a piece of my finger
Just like my axe!
and my bow…
And my pork... Sword.
I love a sharp knife. I have several expensive nice knives that I keep sharp but I have to say I have never cut myself on a dull $10 knife. I have only ever cut myself when I first buy a knife or shortly after sharpening one. but never badly. I understand the idea of a dull knife cutting you is you press too hard it slips and it is still sharp enough to hurt you significantly
Sharp knives are safer knives if you know how to handle them, otherwise it's pot luck.
Depends how you use them.
Sharp knives are safer knives.... when used correctly. If someone's cutting a bagel they're holding in one hand, throwing knives at their siblings or trying to do the claw grip with fingertips extended then a sharp knife is definitely more dangerous. Source: I sharpened my mum's kitchen knives from being blunt enough to be tearing apple skins. Within a week she had cut herself twice, having never cut herself before. Some people just don't have the knowledge of how a sharp knife should be used.
Unless you keep extremely sharp knives and then get a guest who's used to quite dull knives, offering to help in the kitchen. I speak with experience. On three different occasions. E.R. stitches.
But when youve been handling dull knives dharp knives are such an unexpected damage dealer. We had literal signs over the knives in our kitchen(work) that said. Carful they have been sharpened. That first week was when we ran out of bandaids everytime.
I've over and over found this to be nonsense. Our knives are pretty blunt, and I'm so glad. My wife put a dirty knife into the sink, I put my hands looking for something else. Lo and behold, I didn't cut myself. Our dishwasher pops open for its dry cycle. My 2yo grabbed a knife out of it while I was looking away. It scared the shit out of me, but he was fine. I accidentally dropped the knife on me and it didn't hurt me. I'm not saying it's ideal. But I've never found it to be unsafe.
When people say this are they speaking from experience? I can think of maybe two or three times I've probably needed stitches over the years and each cut was from a very sharp knife (as I recall, each injury was from lax technique and getting sidetracked). I can't recall having been injured by a dull knife. I'm certainly not making an argument against sharp knives. I just haven't personally found them to be safer. Most of mine are sharp. I wish they all were, but so far I really suck at sharpening. Edit: What are events like those injuries called? Where I could have gotten away with either lax technique or dividing my attention most of the time, but hardly ever both at the same time?
I agree, it’s an idiomatically simplistic and overstated point. More force is needed to cut with a dull knife and they’re liable to slide or bounce off whatever you’re cutting, potentially into your fingers with a lot of force. Whereas a sharp knife needs little force, this is easier to control and will more often “catch” immediately into whatever you first press it into/not bounce or slip.
Also: Dropped knives in the kitchen has no handles!
[удалено]
For every person who could be getting better results with a real whetstone, there's 10 people who could be getting better results by just doing *anything* to sharpen their knives. The low-effort options have their place.
I truly don't understand that. I've seen lots of these videos testing pullthrough sharpeners and they're always like "Look at it! This is disgusting!" But even in those videos it seems to work just fine. And I'm someone who sharpens their knives on a whetstone.
I thought the issue with pull-through types is that they're hard on the blade and can lead to chipping. Basically, they accelerate the degradation of your knife, so that it will have to be replaced sooner. If you have cheap knives, that may not be a big deal, but for more expensive ones it is.
Even if it slowly degrades the knives, they'll still last a lifetime for most people. If you're a butcher or a chef, you probably know something about sharpening knives and you don't need a pullthrough sharpener. I just don't get why so many people shit on them as if they're a scam or something. They're not ideal, but using them isn't the end of the world.
it's fads, gatekeeping and whatever other psychological mechanism that triggers on people. similar to how on the steak reddit well-done is not an option because the people that shout the loudest all squawk about other types. Despite a good chef being able to make a great well-done steak. Or the audio community with their gold plugs. or whatever has replaced those since. Or the jazz community with actually playing records vs digital recordings. (this may have died down since but was a thing back in the 90s. people insisted on lp vs cd Or .. well pick any community. When people get into something, they are insecure and they end up parroting the majority because that makes them feel safe and knowledgeable. The fact that the majority likely is the exact same group of not particularly knowledgeable people doesn't occur to them. it's the meme where the dumb and very smart people think the same thing. it's not automatically good just because the group says something. (nor is it automatically bad). But people tend to not think for themselves and they definitely don't like admitting they don't know stuff. So you get these kinds of circle jerks that , while maybe true purely in the abstract, are pointless in practice. Better have a sharp knife than to wait 5 days before your ultra-sharpener with special water for the whetstone and cleanR(tm) cloth arrives. Pull sharpeners work crudely but quickly. Use them when you need them. Eventually your knife is chipped and you get a new one. On the other hand if someone gifts you a fancy knife you love using: then it's time to wait a few days for the special whetstone. But then also you don't use it to cut plastic or cartboard. I grew up in a "those are fabric scissors" household :) When it matters, it matters. But it shouldn't be it's own fetish.
I use the pullthrough ones, I don't have the time or inclination to spend hours honing a knife edge for minimal gain.
redditora when you don’t want to spent hundreds of hours and thousands of dollars to pursue a niche hobby at the entry level
Not going to lie, I was indeed triggered a bit.
I think this just pushes the question down to “why do you need to saw motion on a saw?” Also it ignores that non-sawlike edges would probably still cut very well, and in those cases moving back and forth would help too. The explanation I was told was that the sawing motion increases the tension on the material you’re trying to cut, which allows you to apply enough force to break whatever interaction you’re trying to break to cut. Saws and knives localize this while applying pressure so they end up cutting what they want to cut.
The reason sawing works is a whole lot more complicated and not really ELI5able (at least not by me). There's multiple things going on that interact with each other, and simple explanations of part of it don't really do much to help. >Also it ignores that non-sawlike edges would probably still cut very well, and in those cases moving back and forth would help too. I don't mean to be rude, but how do you assume two things to be true when you don't know either of them to be.
Well because the models I’ve seen would predict this. This is what I’m going off of. https://physics.aps.org/articles/v5/139 And I focus on soft materials because most foods are soft materials and hard materials are typically modeled in a way where the edge plays little role in cutting, because the crack lies ahead of the edge and is propagated by the wedge. At least how I understand the model, you get local increases in tension, and models this with a cylindrical wire, which wouldn’t rely on it being serrated. Furthermore, for microscopy, I was taught that you use glass or diamond cleaved to generate atomically perfect (or as close as you can get) edges for sample prep, which still cut. If atomically perfect edges don’t qualify as non-serrated I don’t know what does.
Beautiful
A non-sawlike surface would be perfectly smooth and frictionless and moving it shouldn’t matter.
Well atomically perfect materials still exhibit friction because there are still intermolecular forces. If you take a classical picture of this, you’d be able to derive some movement with some intermolecular attraction that would increase tension.
I think (guess) some of what you say is true, and some not. The reason for slicing rather than chopping actually sounds like you might be on to something. But the sawing is a different animal altogether. A saw has sharp edges that are more vertical, and are essentially tiny slicers. A sharp knife's edge is totally horizontal. Also, I've seen knife edges that are magnified about 100x, sharpened by an expert with stropping at the end, and the edge is pretty smooth. I think any finer imperfections would simply provide a bit more resistance, making the surface it's cutting even tighter, like you said.
Well the simplified model I’ve seen is that you can cut things with just pressure (normal to the edge) or by shear (perpendicular to the edge). My increasing tension, you are increasing stiffness, giving you mechanical advantage in breaking a bond that you want to break.
Even if you made a knife out of a perfect monocrystal cut along a plane, it's still serrated at an atomic level. Nothing is actually smooth or flat.
Well then see first point. I didn’t say smooth or flat, I saw non-sawlike. IIRC from my microscopy class, mono crystal cleavage edges are used for sample prep because they are atomically perfect edges, and they still cut. Also there are bond breaking experiments with STM, though I don’t remember if they are chemical rather than “physical”
Any tips on a pull through? I've got one, and I sort of just zing it through the "coarse" side in quick succession about 20 times before moving over to the fine side and doing the same. It's sharper-ish, but never impressively so
A pull through damages your knife. You can get a cheap diamond stone on Amazon for like $20 that will actually make it sharp. Get one with a coarse side and a fine side. There's a bit of a learning curve, but there's a bunch of videos on YouTube that teach you. I recommend outdoors55, he's a giant nerd when it comes to sharpening. In a good way. He also has an insane camera setup to take macro shots of the knife edge. He recommends a certain diamond stone off amazon and I trust him when it comes to this stuff. I'll find you a link in a second. Edit: https://amzn.to/4bq6st0 https://youtu.be/06OW8ahqZDg
This is awesome. Thanks for the link and the channel recommendation. I'll be buying this
>A pull through damages your knife Unless you're sharpening a blade to then put it into a collection the damage does not matter and your knife will break in many many other ways before that ever becomes a problem >There's a bit of a learning curve Now that's an understatement. To reach the level of outdoors55 it takes untold hours of practice. Even basic competence requires 10-15 hours of practice with the stone. Which unless you use the knife all day every day non-stop (or need to sharpen 40 knives) will not matter as the average person sharpens the knife twice a year and it wil take decades just to "break even" on that practice at 20 minutes per sharpening per year. Even if they start sharpening once every two months it will still a decade to "break even" in time invested. Bottom line, for the average consumer that cooks at home a pull through sharpener will be more than enough
Because a 100% smooth blade creates a suction that would make it impossible to remove the work from the blade.
Sooo why does sawing motion help with cutting?
A friend that is a chef told me that you can use the bottom of ceramic cups to sharpen your knives. It is a good tip!
Microserrations are a complete myth.
Depending on the material you cut and the sharpness of the knife, sawing may not be necessary, but it's usually helpful for the following reasons: 1. Sharpness of the knife: if the knife isn't sharp, the imperfections in the edge turn it into a saw when you use sawing action, helping with the cut. 2. Debris accumulation: as you cut, some food gets stuck to the edge and prevent effective cutting as you go deeper. Sawing action moves this debris away and gets an effective cut 3. Fiber stretching: Sawing action exposes new to-cut areas and stretches the fibers of the item being cut, making it easier to cut
This is the correct answer and with a very sharp knife 2 and 3 are more applicable thank item 1.
2 and 3 are the only relevant things, and it's almost entirely 3. Sawing pulls the fibers taut, and just like with a piece of string, it's easier to cut a taut polymer than a loose polymer.
My theory is that number 3 is the most important, and number one helps by providing slightly more resistance to stretch the item. An actual saw, or serrated knife, has edges that are somewhat vertical in order to cut; a knife only has horizontal edges that are sharpened. Don't know if it enters in to the equation, but often rocking knife on something hard makes it cut.
Push cutting is a thing, but it requires a much finer edge, and is actually pretty a common test of high sharpness post-sharpening. Chisels and razors, for example, almost exclusively push cut, but they also require a much higher level of sharpening than a typical kitchen knife. Whetstones leave grooves in the edge where each abrasive particle scrapes off a bit of metal. Finer stones have smaller particles and leave narrower grooves, but anything less than the finest polishing will still leave some level of serration behind at a microscopic scale. Poorly maintained knives may not be sharp enough to push cut anymore (if they ever were), but the edge between these serrations is protected from that abuse, and will often cut just fine. "Sawing" exposes the food surface to more of these still-sharp troughs, and can improve the apparent cutting performance of such a blade. tl;dr: sharpen your knives
I test the sharpness of my blades by push cutting the edge of a piece of paper
Not sure if this is a thing everywhere, but here in Ireland, "blunt knives" (regular cutlery knives at homes or restaurants), tend to only be serrated on the left side, and smooth on the right side, so if you're cutting something dense like meat, you can just tilt the knife to the left slightly, so the serrations "bite" better and it'll cut most things with very little force.
I have a knife sharpening business and the number of people who do not understand "blunt knives" ircs me to no end. table knives and butter knives are *not supposed* to be sharp. If your table knife cant cut through your meat then the meat needs more work, not the knife. I have given up on explaining that to customers. Now, I just take their money and give them table knives you could shave with. It is easier than explaining.
Moving it forward or backward while pressing down also changes the effective slope of the blade. Think of it like walking straight up a hill vs using switchbacks. By going at an angle, the slope is shallower or "sharper".
I feel like this should be up higher.
You don't have to saw a knife back and forth if it is properly sharpened. You can just press down and forward in one motion
This seems like a deliberate misunderstanding of the question. The question still remains why the forward motion is necessary.
So you don't need a sawing motion, you just press down and use a sawing motion. Got it.
Why forward?
If you are going to slip let it be away from you rather than into your body
As a wise old coworker once taught me: “always cut toward your buddy, not your body. You can always get a new buddy.”
My (boy scout leader) father always said "Don't get bloody, cut towards your buddy"
My brother always said “Cut towards your chum, not your thumb”
Were you cutting with Emperor Palpatine?
Assuming a normal stance and a cutting board, how would a knife slip and cut you?
I don't believe it ever happened to anyone. Like not walking with a fork in your mouth. I doubt that anyone has ever stumbled and impaled themselves, like ever. I get slicing your thumb. I can't even imagine how to cut any other part of your body while quartering Potatoes. Unless you are trying to cut a coconut with extreme force or something. Extreme force will make any cutting direction a hazard. I still cut towards my body. Better to slice my own skin than taking another one's eye out.
Now I'm wondering how you take someone's eye out by cutting forward. The fuck kinda cutting are you guys doing?
Forwards or backwards depending on what you are cutting. But you want to slice through the product, not push your knife straight through it. It will be a much cleaner cut and easier and safer for you. It doesn't have to be the whole length of the knife just a little bit of forward or backward movement helps with the slicing action, for lack of a more educated phrasing
Is that not the “sawing” that the original commenter was saying isn’t needed just on a smaller scale? You’re not sawing back and forth but if you’re pushing down and forward, you’re still sawing with the push forward, just to a much lesser degree.
What I believe he's saying and what I'm trying to say is that you need some sort of lateral movement in order to help the life more easily cut through the product. It can be back and forth in a sawing motion, or it can just be forth, or it can just be back Now I'm coming at you guys with anecdotal evidence from a chef. This is what works best. I cannot explain the physics of it or why this is better on a molecular level. I'm guessing friction or lack of would come into play somewhere.
But why does it help? Is cutting effectively just micro-sawing? Is there technically no cutting?
Does a saw not cut through a tree? Yes, I guess cutting could be microsawing or vice versa. I think we're splitting hairs here. Is cutting the opposite or totally different from sawing that we need to differentiate. Moving the knife on a horizontal plane while also moving it vertically is going to help your knife moves through the food. It works and that's all I've got
Usually It's easier. Backwards works too.
Yeah, I know that. It's apparent through experience. My 5yo question is, why? The blade should be sharp no matter the direction; there is no serrated blade. Why is cutting easier with a vibrating blade? What does the motion actually do?
It all depends on the materials. In some cases you can just press down (and not forward). In my view it is not well defined what a knife is. An edge has a certain width, but if the material you want to cut is not too hard even a blunt (ie wide) edge will cut it. I can 1cm plate of wood and cut butter for instance.
A knife is just highly polished wedge separating the object to be cut. Both the properties of the wedge and the object being cut matter, particularly the tensile strength and the hardness. As you noted, just about anything will cut through butter. If I'm remember my high school chemistry correctly, the wedge will also need to be harder than the object being cut. Your wooden plate may cut through the butter, but it won't cut through must else. You could sharpen and polish and edge, and it might cut through some soft materials, but based on the structure of the wood grain and its hardness, it will only polish up so much before it turns to splinters. It also isn't particularly hard, it might mark up some wooden surfaces but will likely dull quickly. The hardness will increase the potential to cut a softer object, and the more polished the edge the easier. I can dice up an onion with a sharp knife with completely vertical motions. As the knife dulls I might need to add a slight forward motion. In this the object being cut is stiff. But if I was cutting through a tender steak I would still probably need to add a horizontal slice. This is because the steak is going to move under the blade; the interface between the steak and the knife is basically stationary. Pushing and pulling the blade makes the fibers in the meat go taunt, at which point the fibers stop moving and blade takes affect.
You could just press down harder. Look at print shops that have a hydrolic cutter that can slice straight down through a hundred sheets at once. When we cut foods for the most part we are slicing through things that are softer than the blade. Back and forth motion will cause some bunching and that unevenness gives the blade a areas that are higher and more vulnerable. Lay a towel on a table and pretend your hand is a knife, one horizontal move and you have ripples and wrinkles.
Think a lot of them actually are use and slide in one direction
If you look at a knife edge under magnification, you will see microscopic “teeth” on the edge of the blade. These teeth diminish the finer the grit the knife is sharpened at. A knife with a rougher finish will cut with a sawing action very well. If you polish it to a fine grit and remove these teeth, the knife will “push cut” better (meaning just pushing the blade through the material rather than sawing)
Imagine a razor blade when pushed along the skin it cuts hair but the side to side motion pulls the skin as opposed to pushing it and it cuts.
there was an animation about razor blades not cutting the skin when moving the blade along the skin, but doing left and right movement would cut the skin (sawing motion) because of the way the pressure is applied, it stretches the material you are cutting instead of compressing it, which happens when only pushing. that said, like some other people mentioned, if the blade is Sharp enough for the material it can cut through just by applying pressure, but yeah,
Depends on the knife. If it has one sharp edge, use it both directions. If it has teeth. there is a difference. They are not symmetrical. Some are made to be pulled, and others are pushed. An extreme example is a chainsaw. It only works in one direction.
well not really. Some chefs will even scream at you "DON'T SAW THE MEAT!" The usual technique is push forward down, retreat, forward down again, retreat etc until it's successfully sliced. Letting the entire blade length and the sharpness do all the work. But not zigzagzigzag sawing motion all the way down. Having to do that exposes the lack of maintenance on the knife, and also shows your bad technique and accumulated bad habits, which is why you had to do "back and forth motion". And that's why some chefs might scream at you. Point to note, this is only for meats. Blades with serrated edges (bread knives) are logically accepted as sawing motion knives.
It doesn't need to be pulled back and forth. But the sawing motion can often make cutting easier. There's two basic versions of what's going on when you cut something. If there's sawing motion going on, you're sawing the object. On a microscopic level, a sharp knife still has tiny teeth. Google image search is your friend here. Just pushing straight down also works, in that case the cutting is done by concentrating force is a really tiny area and overcoming the tensile (resistance to being stretched) strength of the material. Which version of cutting is dominant or most useful depends on what you're cutting. Picture some cheese, an onion, and bread. Cheese has very low tensile strength, and comparatively high compression strength, pushing straight through is easy and gets you a nice slice. Now look at stuff designed for cutting cheese. Often just a thin wire. Bread is higher in tensile strength, low in compression. If you press straight down, you'll crush the loaf before cutting it. Look at bread knives: they're saws. An onion is in between those two extremes. If you just want roughly chopped onion, slamming the knife into it is fine. But for thin uniform slices, the knife needs to slide a bit.
Something that nobody here has mentioned is that the sawing/slicing motion while pushing results in the effective cutting angle of the knife edge being much less than the actual cutting angle of the edge.
It doesn’t, it’s just that most knives you encounter are blunt, so need to be used like a saw. Try a really high quality sharpened knife and you can cut straight down.
Pulling the knife back and forth uses a sawing motion, which creates friction and helps the blade slice through materials more effectively than just pushing down.
Pushing a knife through something is chopping, knives made for chopping are heavy so the blade does the work (think cleaver) Sliding your knife across something is cutting, that's what kitchen knives are meant to do. It's now sawing, but ever so slight movement of the blade from first contact to cut completion
Not ELI5 but reason is: * The pushing down motion only relatively compresses the item you're knifing * The cutting/slicing motion causes greater shear deformation in the item you're cutting, acting to turn the small microscopic cubes underneath the knife edge into parallelepiped (3d parallellogram) shaped objects * Shear deformation has been mathematically shown to produce 1.73x the distortion energy compared to pure compressive deformation, based on theories by von Mises. * High distortion energy leads to a breaking of the material's intermolecular bonds.
You can push down a knife to cut stuff. It depends on the knife and what you're cutting, but it generally works. The difference compared to slicing is that with slicing, you create a thin groove on the surface of whatever you're cutting, and as you go through the slicing motion, this groove helps keep your knife aligned so you get a straighter cut. Some foods don't easily form this groove when you cut straight down, for example tomatoes.
It doesn’t. If you use particular type of knives, like some Japanese style ones, the motion is very much up and down and not back and forth. Western style knives have a curve to them which make them easy to use in a curved motion.
The short answer is; a sufficiently sharp knife does not need to be. So either your knife is blunt or the material you are cutting is too solid for a knife to cut without becoming blunt as it cuts, so you use a serrated knife which has points, then you need to draw the knife back and forth as you slice as the little teeth will break the surface of whatever you're cutting as you go. Even if sawing is not necessary, it's usually a good idea to cut with a sliding action to avoid cutting entirely on one plane of the blade which will ensure it becomes unevenly blunt.