Over Center Mechanisms But Were Afraid To Ask!

[Music] [Music] pap [Music] [Music] [Music] as some of you probably know I'm the proud owner of a couple of kids what you might not know is one of them is a teenager and the other is teetering on that teenage Edge so no surprise maybe but they're at that age where they're asking difficult sometimes embarrassing questions and you guessed it they're asking about over Center mechanisms as a dad it's my responsibility to leave uncomfortable questions to their mom but then I thought but you know what what if they're asking questions maybe you're asking questions too this is an over Center mechanism isn't it beauti okay fine it's not much of a mechanism but we've got to start somewhere can't just dive into the deep end some context for this video over centers or over Center mechanisms for short aren't really that complicated to be honest and they fall under the umbrella of by stable mechanisms mechanisms which only have two stable States A or B on or off left or right how hard can that be it's only two for crying out nonetheless I've always found a beautiful Elegance in them they solve a lot of problems simply so with that said if you're as by curious as I am well you're going to love this video let's take a close closer look at exactly what's happening here we've got sort of this upside down stick and a screw that combination lets it rotate about that point these two DS here are just from keeping it from spinning around like a clock they're just stops those will turn out to be very important and an integral part of this whole thing yeah there's some sort of pseudo stable State a position right in the middle where you can kind of balance it but that position can't be trusted on either end though it is rock solid as simple as that seems to us now you might be surprised to learn that it wasn't until like 1687 that people realized it was gravity that made this thing work and only 50 years after that did they realize that it doesn't work upside down it's useless now what's going on here to State the obvious is that gravity is holding that link up against these stops if I can manage to animate a little arrow in here that's gravity trying to do its thing and pulling it down against the stops so we've got a force going on here that's pulling the link up against the end stops that doesn't do such a great job when it's upside down gravity is still doing its thing but now our end stops are up here what we need is some other Force that's not going to depend on Direction maybe you see where this is going do you know what this is It's a spring this is a spring this does not rely on gravity is that not just the coolest thing you've ever seen yeah I could have used a counter sunk screw in the middle so I'm not running into that spring now we've got that spring Force always in the direction sort of making the link hit the hard stops and pulling that link over Center and we we can now use this really cool mechanism any way we want upside down sideways backwards heck even in the cold heartless vacuum of space where there is no grab odds are you've probably started to recognize this thing these are absolutely everywhere maybe you recognize it as the kickstand of your bicycle that cupboard that keeps itself open or even that light switch on your wall I wasn't going to do this build a mechanism with a gas spring but with this 30 lb grill in the room you'd be remiss not to or I would somebody go missing anyway although gas Springs like these are usually used to assist say lifting a heavy door we can use it for an over Center mechanism it'll be exactly like the extension spring we just used but this works in compression this spring pulls and this one pushes we'll build something crude around this these come up a lot and we'll just use it to talk through the process think of it like a homework problem this little bugger hardly over a/ inch in diameter and what maybe 10 in long Believe It or Not puts out a whopping 130 Fig Newtons of force AKA 13 kg AKA again around 30 lb I know it's a 30 lb cylinder because of that shiny black color that and the label on the bag it came in I'm not sure where these things come from iume they're minded out of the depths of hell but these little marbles of engineering and we could probably talk about these for days have two key takeaways first this one's really important they can be dangerous these could knock your teeth out in a Flash and two they are constant force that means no matter how much I push them that's 30 lb still 30 lb still 30 lbs just pause the video and think about that for a minute a regular spring pushes back the more you push on it squish it a little it pushes back a little double how much you squish it and it'll push back double this is constant how on Earth does it sorry about that that was all sort of besides the point I tend to go off on tangent sometimes meet the finger Chopper 2000 here I've got a little door mockup this could be a cabinet in your garage a window maybe a toolbox on your truck it's not important and what I want want this box to do is stay open when it's open all by itself and stay closed when it's closed all by itself I'm going to use this guess basically we want this mechanism to go over Center let's think about this for a minute without the spring and talk about exactly what we want to happen well when the door is down like this when it's closed we want a pulling force on the door keeping it closed a clockwise torque around this hinge we want it to keep moving clockwise but when we open the box when we lift the lid we want the force to keep pushing it open we now want this torque to go counterclockwise when the door is open we want it to keep pushing open so your job here should you choose to accept it is to somehow install the spring so that it changes the side it pushes on depending on where the door is I mean that sounds outright crazy when you say it out loud before we go twisting our brains in the pretzels I have a little problem to solve I have no way to connect this gas Spring right now it's just got threaded studs on the end can you see that will that Focus I don't have what would be eyelets for this gas spring so let's make a couple first thing we need to know is that thread size going by the taste these are M6 metric threads if you're not a thread connoisseur like I am you could use thread gauges to figure it out well would you have a look at that that we've stumbled into a teachable moment these parts should have been exactly the same but in my haste I made waste waste we're going to use anyway but check that out I inadvertently switched to a different reference which I thought was the same I drilled the holes based on these shoulder locations but I cut them to length based on the boss had these bosses been the same length that would have been great but they're not H I've ended up with a thin wall on the back of this eyet now since the gas Springs are always in compression the forces should always be pushing into this connector into this eyelet and I shouldn't risk blowing out that back wall that and I don't feel like making these again that screws on there that screws on there and we're now well on our way to really hurting ourselves to recap we want to position the spring so that it sort of switches sides or goes over center with the swing of the door if I were to just attach the spring here it's going to be trying to push the door open and when it's in the up position it's still going to be trying to push the door open but if we look close and this unfortunately is where my little mockup door falls short if we were to attach it to this side of the hinge there's not enough material there here it would be pushing up clockwise closing the door but the geometry of the situation is such that when you toggle this it sort of flips over to the other side and would be pushing it open that's basically what we're trying to do in a re door application you probably wouldn't have a feature like this you'd have just a regular hinge probably somewhere else on the box so to make up for that shortcoming I'm just going to add a second tab down here somewhere this might just be a gusset coming off the back of the door or a bracket that came with your gas spring let me just take a moment I don't know where this scrap metal has been but should be happy you're not around to smell this this is a little bit thicker it's going to throw my piston out to whack a bit just cuz I needed enough thread engagement to not have this thing shoot across the shop one thing you always want to keep in mind with these gas Springs is that I mean apart from the force now there's also sort of like a twisting motion at the mount Point like when this goes under load you see it's kind of like up higher from the hinge point it's trying to twist this bolt out and sometimes that mounting torque can be pretty severe here comes the scary part I need to get this hole to line up with that threaded hole and I'm going to do that with a clamp hopefully I'm going drop this on there just as a spacer and I think that should be it let me clamp this down to the bench all right there's nothing in front of me should this piston take off that way and it should miss my heart where it to come this way stays open stays closed [Applause] open closed if you just let out a squeal and thought to yourself all right now we're getting to the good stuff well let me know down in the comments maybe we can get a better group rate for therapy before I unveil what's inside this jar let's just take another quick look at the two over Center mechanisms side by side in both we have a spring that's moving a link over the center of rotation and driving them up against the hard stop you can think of both as sort of Three Links if you count the board that they're mounted on There's the link the spring and the board the link the spring and the board sorry if this one comes off screen it's too big those three links make it a really strong and stable triangle shape the only real difference is that this one is pulling the link over Center and this one is pushing the link over Center but for these to work in either case one of the three sides of the triangle had to change length to get from one position to the other you follow that with the gas spring it needs to get shorter to clear that swing with the extension spring this spring needs to get longer again think of it as a triangle if one of those three lines can't change length then nothing can move and in both cases that was the spring in fact Springs are nice because they can create a force and change length some might even argue they create Force because they change length but who's to say I'm sure we've all used these fliptop bottles and jars before up it opens down it closes but do you see a spring in there anywhere anything at all that could change length or develop a force let's have a closer look I went out and bought the absolute cheapest jar I could find in the hopes that this would be very visible and it looks like my $2 gamble paid off big time just look at how much those wires move sure there's a rubber gasket in there or something that looks like rubber but it's a 16th of an inch at best way less than these pivots are moving if these wires were wound a little better a little tighter this jar would never close but let's look at what's happening mechanically out here is the hinge where my sort of lever rolls around the pivot for my link in this case the part holding the lid closed currently is sort of under and inside the hinge when I pull this around it swings under and and up to the other side and right there where you see sort of that most Force happening is where it's flipping over Center there's the triangle we saw before because the pivot had to go over that Center the forces from these wires and that gasket are now pulling on one side or the other in this case they're pulling such that it's keeping the jar closed up against the hard stop in this case the glass jar ever have your knee like Bend too far backwards and it locks up on you well it's the same thing here and fun fact jars feel that same exact pain every time you close them all the same Parts as before but arranged in a slightly different way and cleverly made with some bent wire all to produce this functional latch or barely passable latch in this case here however there's one small but very important detail we didn't have to worry about in our spring versions check out this part of the link here that short section how long that link is determines how far over Center we're trying to push this whole thing like the longer this little short section is the more Force we'll need in this case if it were longer it would probably bind and you'd never get it to close without breaking it if it were shorter it'd be a heck of a lot easier to close but you might not get a great seal easier to close but it' be a poop jar I mean not a poop jar that's a different video I mean very low quality when used as a latch like this over centers are absolutely everywhere you probably know them from such popular films as tattered toolbox latches beat up boot latches heck even this barrel clamp I found accidentally mixed in with my nipple clamps uses just one big over Center latch I don't have much time with this one as my pants are already on their way to my ankles but check out these suspender clamps can you guess what that is is it an overset well it sure got chili in here all of a sudden pretty smooth transition to locking clamps eh we've all used these clamps right I don't need to tell you that they just lock on when you squeeze them no fooling around with finding the right size or running screws up and down like your grandpy C clamps right well no they're still a screw you maybe don't directly tighten your work with this screw but you need to set it for the thickness you're trying to clamp thickness and pressure I guess if you set these two tight they're what can anybody guess anybody that's right they're too tight I can't get them to lock on I need to adjust them so I'm just at that point where what anybody anyone right again you have to adjust them so the length inside can just snap over center now it's clamped on the harder you make that link fight to snap over Center the more clamping Force these will develop it's not the easiest thing in the world to get a look inside here so let's bring out it's kissing cousin the toggle clamp these are exactly the same but completely different let me just on this toggle clamp you can sort of see all of the links in the pivots so it's just simpler to talk about but both have a lever you move to clamp and they both have a screw that needs adjusting just like these locking clamps all that force that you generate squeezing the handle or pushing the lever in this case is transferred to the clamping with some mechanical advantage sprinkled in and they lock keeping all that clamping Force really bearing down and just like that knee of yours that likes to bend backwards no amount of force trying to lift this clamp will unlock this mechanism the geometry changed that pivot went over Center and now it's trying to rotate the wrong way if I try to open this clamp it's just driving all that Force back into itself completely bound up and nothing you could put a 6ft cheater bar under here and nothing is going to get this lever to come back up cuz it just physically can't to break up the monogamy let's walk through this one a little bit differently it's exactly the same as everything else we've seen but we'll use different words this time though I still want my triangle first thing you might notice is there's no spring here but the fact that the clamp end can rotate means that the green line can change length it can get longer that green line also happens to be our quote unquote center it's called our Center Line Now watch how as I swing the lever the top pivot goes past that Center Line it goes over Center not a lot in this case what might that be 20 30 th that's why these clamps can be finicky sometimes when you're adjusting them not a lot of margin depending on what you're clamping but it goes over Center it goes below that line so who cares why is that so magical you might be asking your loved ones well this time let's look at the clamp back to front let's start at the clamp side this time it's clamped down squeezing something which means what you're clamping is trying to push back it's trying to open that clamp so that clamping force is trying to rotate the clamp up which in turn is pushing back on her handle but look at that little link it's now below the pivot point so the pivot link is trying to move down clockwise wasn't like that when we closed it and it can't it's run into the frame and just like having too much Olive Garden it's all bound up now when we swung past Center we Chang change the geometry of the links or you know how they can move where they can move and releasing the clamp pulls that point back over Center frees up the whole thing and drags the other links with it it's freaking magical I wasn't sure if I'd bring these in for this video or if I should wait for advanced obvious mechanisms to come out but if you've made it this far it's time to unplug you from the Matrix from here on out there is no spooning don't try to adjust your television Vision you are indeed looking at a plastic top with an integrated lid none of that twop Parts box with a separate lid nonsense we're 21 minutes into the future since you started this video and in the future everything is one part just have a look at that talk about Elegance I mean where does the lid even end and the Box begin right there at the hinge but the hinge is molded in it's part of it same piece of plastic as the rest just maybe a little thinner at the bottom and it does exactly what you'd expect thin plastic to do it bends but have a look at this one also one piece of plastic however well that's different that looks like it's going over Center and fabulously so at that I'll cut to the chase here if we look close you'll notice two other little features on either side of that hinge symmetric features again all one piece they're just thin plastic webs of the same part and while that one in the middle is acting like a hinge the two on the sides miraculously almost are acting as Springs they have managed to make this but out of one piece of plastic instead of eight or nine Parts I get Shivers just saying it out loud but that hinge in the middle you see it it's wide enough that it forces the lid to rotate around its axis the thin webs of plastic on the sides are further out and further back from that axis because this lid is round that means when the cap rotates around the hinge the two Thin webs need to move through a larger swing a longer distance than the material in the hinge does and that stretches them once they pass the top of that swing the most stretch they snap back pulling the lid the other way they snap over Center have a look at this one much flat profile on this lid the back is almost straight not as round as the other one the webs on the side don't have as far to stretch so the spring action it's there but it's a little weaker that's not a bad flip top but it's definitely not as satisfying as this one if I'm being honest it's a bit of a let down I'm man enough to admit that I've gone through entire bottles of shampoo in one shower just to be able to flip these tops just one more time the nuances though depending on which specific cap you have in the shower can sometimes get a bit complicated go have a real close look at a few flip tops of your own and maybe you'll see what I'm saying sometimes the thin webs go through what looks like oil canning like Snap through they sort of buckle one way or the other you know those poppers or whatever those toys are called that you turn inside out you kind of put them on the table and then they slowly snap through and jump up in the air something like that but when the web snaps through it forces the lid a specific way however your favorite fliptop Lids work and let's be honest we all have a favorite there's one thing that's always amazed me even more than the fidget Factor all of these caps are injection molded that means there's a mold two halves closes they squirt the hot plastic in it cools down they open it and the parts fall out to mold a cap like this it has to be done in the open position so that's how it would sit in the tool cap straight back so you have access to all of the features that you need to mold someone had to design a cap in the open position and cross their fingers for 6 to 8 weeks maybe more after they spent a half a million dollars of someone else's money to find out after the cap was molded if it would even close let alone Be Snappy that's so high of a pucker factor that frankly I refuse to believe it now I've never been able to figure out who first invented these in part due to the fact that I've never cared enough to look into it but I like to believe someone was making a regular cap with a regular vanilla hinge Nothing Fancy no over Center no snap action and business doing what business does best probably ran that injection molding tool into the ground making millions upon millions of caps until the steel just wore out and the parts started to flash flash means the tool didn't quite close as cleanly as it did when it was new usually because some steel is wearing away or misalignment issues but maybe you know what I'm talking about you know those razor sharp edges on Old cheap plastic coat hangers where the plastic starts to sort of seep out of the mold and create those sharp knife edges well I bet that happened with the cap I bet that flash started to create a web of material around the hinge just a little but enough to make some quality control Tech notice the cap was snapping over to notice that the cap was opening and closing by itself like any good machine operator or QC person they hit the big red EOP and they ran that part up to engineering who then consequently took full credit for the design of course I could be wrong maybe it was designed this way from day one but I like my story better and speaking of stories I think that brings an end to ours I don't know who this video was for who needed to see it or what they might do with it but standing in the shower the other night all pruny handed and my wife screaming through the door not to finish the shampoo she literally just bought the D right then and there I knew this was a video I needed to make perhaps so I could start the healing process if you made it this far I appreciate the company and as always thanks for watching

Channel: This Old Tony

Views: 382,737

Keywords: over-center, overcenter, over center, self-locking, mechanisms, clamps, locking clamps, toggle clamps, living hinges, plastic flip top

Id: Ia3Iieejyg8

Length: 26min 40sec (1600 seconds)

Published: Fri Jun 07 2024