Shear Pins are Smart (They're Mechanical Fuses)

I broke my tractor in a field. Instead of getting upset, I decided to celebrate the marvel of shear pins. A friend called them "Mechanical Fuses".
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Warm Regards,
Destin

[@WilliamDye-willdye]

It's just a quick one-take clip, but in a way, this video truly fits the title "smarter every day". We get the role model of a person who keeps their eyes open, eager to learn more about the world around them. I also like that the video is short, and covers a genuinely interesting concept.

[@JulianSammy]

Mechanical fuse - what a great analogy! Thanks, Destin.

[@Trident_Euclid]

Julian Sammy literally

[@op4000exe]

And this is what a failsafe really is, some people think a fail safe is a part that makes a system not fail, this is not the case, a fail safe exists to make sure that when the system fails (which it will eventually no matter how many preventative features you include in it), it fails in a way which does minimal damage, and is very easy to contain. So in the future if you try to design a system you don't want to fail, don't think you can make a system which won't fail (ex: Titanic, by which I refer to the lifeboats), design one whereby failure is not that big of an issue.

[@aarons8711]

Good comment, but Titanic did have fail safes. the underside of it was split up into sealable cabins, but when the captain tryed to steer away from the iceberg, he ended up with a long gash across the side of the ship that hit too many cabins to recover. Ironically, if he had hit the Iceberg straight on, and hadn't tryed to avoid any damage, the Titanic would have been fine.

[@op4000exe]

I was refering to the lifeboat situation of the titanic moreso than the hull, I know about the fact that the hull was split into different compartments. I'll just edit the comment to include what I was really refering to. Thanks for pointing it out though.

[@ferky123]

magical potato There was a flaw in the design of the watertight compartments on the Titanic in that there was no roof on the compartments so that when they filled up they just spilled into the next one.

[@glitch1299]

Better for something to have a failsafe then be faildeadly

[@andymcl92]

glitch1 I think Derek at Veritasium had a video on this that's worth checking out :)

[@chipmunk449]

You just blew my mind with the simple thing of saying it's a mechanical fuse, no joke i don't know why but I find that awesome.

[@PostManUpsideDown]

where other people would beat their tractor with a bat in anger, destin makes an educational video :^)

[@spelunkerd]

This is how a successful person deals with a problem. What a great attitude, one I aspire to every day.

[@zedex1226]

PostManUpsideDown angry? no, I'd grab a bolt from somewhere redundant such as one of the many bolts holding the seat onto the tractor, pop it in and keep working.

[@myfavorit3rifl3]

PostManUpsideDown i always carry extra shear pins while mowing

[@PostManUpsideDown]

sorry im such a city slicker :(

[@jakewagner7416]

it's better to choose where the failure will take place as opposed to the accident choosing for you.

[@SpartanXx666xX]

Umm this is how you end up in Interstellar.

[@SmarterEveryDay2]

Visesh Velagapudi one second let me hijack a drone in this corn field.

[@82ayalaj]

Visesh Velagapudi best comments ever!

[@Keys879]

Well you'd be the guy Destin.

[@StaticImage]

Videos like this are really cool. Short, to the point, informative, fun. I dig it.

[@brandonscullion]

Destin says he has a tractor and we all go OF COURSE HE HAS A TRACTOR.

[@jimsteele4017]

Great video Destin! I learned about shear pins as a teenager; Dad had this OLD outboard boat motor that would break a shear pin on the propeller shaft about once every fishing season. After a couple we learned to keep spares in the boat! (I asked Dad, "Why are they made out of aluminum? If they were steel, they wouldn't break!")

[@P-B-G_YT]

In 1982 as a 19-year-old Heavy Equipment student, one of the pieces of equipment I got to learn was an old mechanical Caterpillar D12 Grader. Everything ran off of a power-take-off from the engine. All the controls that moved the blades worked mechanically, there was no hydraulics. There was no starter motor on the grader. It needed a push-start from a bulldozer to get it going. It was still winter, late February, many of the machines didn't even have batteries. During one pass along the roadway we were clearing snow off so we could start the class, I dug the blade in too deep, and the torque somehow snapped the shear pin. The machine had to be stopped so a new bolt/shear pin could be dropped into the hole. Once that was done, a bulldozer had to push-start the machine while the blade was still down. Even with the blade down, the bulldozer didn't have any problems. Funny part about the bolt, it didn't require a nut to hold it in since it was held in place with gravity. All they had to do was carry a handful of spare bolts, and drop one in when they sheared off. Usually it was done with a machine that had batteries, so they could quickly re-start them. Thanks for the video.

[@hackleberrym]

Wait, what? You're a farmer now? o.O

[@00Linares00]

No, he is just from Alabama

[@DjowsSr]

And I thought he worked for NASA.

[@harshav_me]

KZbin revenue isn't enough these days

[@Keys879]

Don't gotta live on the Moon to work for NASA ya know...

[@toshley6192]

Nah that's just a big lawnmower for cutting big grassy fields, not actual farming. They're good to have on acerages (large plots of land in the country that people build a home on, without actually cultivating the land for farming purposes). They're common in North America where land is abundant.

[@HiVoltish]

We have them in linework too, the crossarm itself is a type of mechanical fuse. In the event of a storm the crossarm, much less expensive than an entire pole, will break first. Love the analogy!

[@DP69264]

I'm a jet engine mechanic in the Air Force, and all components that spline into the gearbox and accessory drives have shear points. The only drawback is that sometimes those shear points fail on their own. On the landing gear where a tow bar hooks up there is one bolt holding the tow point to the rest of the aircraft. It too is there for the same reason, so if the plane suddenly stopped, say from a tap on the brake pedals, it would shear and not damage the landing gear. I love watching your channel!

[@blinkercek]

This is exactly how Smarter Every Day should look like. Showing people they can learn something new every single day.

[@MateusHokari]

Getting smarter everyday

[@Just_me_73]

I like the character he have. The way he mange a hard and nasty situation. Take advantage of it and give us some thing cool to learn. He knows ho he is. How he likes to live and must important. What makes him enjoy life. 😃

[@jonathannagel7427]

Destin: from a fellow Engineer & aeronautical geek, I'm glad you took the time to explain what much of the world doesn't even know exists. I had a triple-blade Husqvarna riding mower & I'd go through about ten shear pins/year. Fortunately they were inexpensive (& much smaller than yours, with a specific "soft spot" notch in them, much like a .22 bullet casing.) I love that you made the comparison to a car's drivetrain, as right now I have the heavy, worn out flywheel from a '72 Porsche 914 holding down a tarp on my truck! And to talk about serpentine belts; getting those three blades realigned so they don't strike each other, along with the getting the belt, on the cogs was... not easy.

[@blackpete]

Funny, you seem happy about your damaged tractor... So much positivity. And you share it with all of us. Thanks, man,even though I knew about "Sollbruchstellen" like this.

[@ShawnP1989]

Shear pins are everywhere. Basically anything with a spinning blade or auger of some sort have them. Tractors, earth augers, lawn mowers, snow blowers, boat props, etc. Never thought of them as a mechanical fuse though, pretty cool.

[@TheBetterGame]

I work in a mine. We use large shear pins, upwards of 2inch diameters. We don't call them Smart, we call them "Damnit, now now!"

[@SeanBZA]

Considering the result of them not being the weak point is a serious rebuild of a mangled conveyor they are cheap enough. New operators i always would have to replace a few taper pins till they had gotten the training fully ingrained, but the pins were a lot cheaper than the machine, and I also have a large supply plus importantly a taper reamer to massage the hole back into shape for the new pin. Of course sometimes the 65RC dog clutch did not like the manhandling, and shattered instead, but that was still fixable.

[@natepressel6747]

Don't forget Destin, the really smart thing about the shear pin is that its a readily available bolt from the hardware store. They could have made it a key-way or some proprietary connection that would force you to buy their special bolt, but they didn't! Also not over-engineered slipper clutch or ratchet mechanism that can seize or be more expensive to produce or fix. They know their customer, that's good engineering.

[@rydaddy2867]

Some do use a special-grade bolt (not exactly Grade-5 or Grade-8), but a shear pin is common enough that most hardware stores still have shear pin bolts in stock.

[@Joecool20147]

This is a perfect example of why I subscribed. There are so many questions in the world and solving them is supremely interesting and entertaining. And some people can just understand problems and design, and then explain it in a way that instantly makes it click. From one undergraduate engineer, to a post-graduate engineer. I love it Destin, I'd also love to one day get an aerospace masters degree, just like you.

[@LeeFluff]

Frangible design is a super useful specialty for re-usability in any impact-absorbing system. I always have respect for designers who use these kind of critical load capacity items in their design, because it really shows they understand the scales of the loads going through the systems, and how they want to be able to salvage and recommission a set up after 'failure'. Explaining the concept of a "controlled failure" to laypeople is always fun... because returning an item to serviceability quickly is acceptable design, and often preferable, over beefing up a system to inefficient proportions to be able to resist this load in capacity.

[@Schmidtelpunkt]

Krone SafeCut takes that idea one step further. There are several discs in a mower, all cutting at the same height. So when one gets stuck, that safety bolt breaks and a mechanism lifts the whole disc out of the path of the others. I sometimes edit videos for agrar machinery, and seeing the simple and robust but very fail-safe methods those engineers come up with, are the most interesting part of that job.

[@DogiojoeXZ]

This is very common in household vacuums for the same reason. There is a nylon drive gear interacting with a brass worm gear. When you suck up a shoelace and lock the brush, it shears the nylon gear instead of the expensive brass worm.

[@chinaman1]

the sad thing is that not many people understands the point of having these intended weak points and sees them as poor quality products that breaks off easily due to lousy quality. I'm so glad that you made this video, so i can show to my clients in the future that shear pins are made to fail.

[@tatdexter2334]

From tractors to ballistic missiles. One of my early jobs on Peacekeeper (MX or LGM-118) was working with a part that was driven to a mechanical stop and had to disengage quickly. A pure silver shear pin did the job nicely.

[@RealLuckless]

And really smart designs for shearpins include holders for extra pins nearby where they're used... (I've seen a few really slick pieces of equipment that even have simple contact switches in the spare sockets - The machine will make an annoying error code noise on startup if the spares aren't there to keep you from using the spares and not bothering to restock them.)

[@kg4boj]

If you hit something hard enough to break those shear pins with a mower deck you REALLY need to lift up the deck and check the spindles/blades for damage. Those blades are going around 400 miles per hour at the tip and hitting anything that would stop them dead WILL do damage. You definately don't want to just throw a couple new pins in there and see how it goes. The pins limit the damge to the tractor's deck leaving the PTO unharmed. That definately doesn't mean the mower deck is just fine!

[@zedex1226]

nah. it's a VERY good idea to inspect them but the odds of really damaging them (especially from the tire he said he hit) are low. I've turned cinder blocks to powder, carved 3" chunks out of 2' rocks, tangled and torn cyclone fencing, mangled 1" mild steel pipe. many hundreds of hours mowing scotch broom, 1-2" alder trees, only broken 1 blade once. those brush hogs are no joke though, a serious piece of machinery the way those 15 or so lb blades whistle around. Do be sure to treat em with all the care and respect of a firearm. all the safety all the time and no one around that doesn't need to be.

[@ElectricGigalo]

I literally just saw your Snapchat about this. I was intrigued and came to check your channel to see if you had more info, and I was stoked that you had done this. Dope. 🙌🏽

[@sthompson4966]

This is a great video, a window of rural life, engineering and observational skill. Thanks for passing on you observations. Your a real teacher at heart.

[@marakanda]

Gotta say thank you, for lightbulbing me into a process for fixing my lawnmower (forgot all about stupid mechanical fuses). Saved me ~ $150

[@Y2kovu]

The quote about having nothing left to take away comes to mind, looking at this. Neat!

[@elementsenjoi]

Another method commonly used on Bushhog drivelines is a slipper clutch. Clutch plates in the driveline are bolted together with springs holding a certain pretension on the plates so that if the load spikes the clutch will slip slightly to prevent damage to the tractor. Cheers!

[@humpday75]

now this is getting smarter everyday, love your vids Dustin, I wish there were more people that is interested in more than one job

[@43bikeguy]

This is why I subscribe to your channel. The wonder of science and engineering everywhere and in every situation.

[@crispyspa]

if you look at the top of the bolt there are probably three lines arranged in a circular pattern around the head, this means it is a run-of-the-mill grade 5 Bolt. Go to the hardware store and match it up. pick up about 6 of them and throw them in the toolbox

[@David-jp5mo]

Yup! They have the same thing in snow blowers! When you come across an unexpected newspaper or water main cap it's really annoying but smart since it's much easier and cheaper to buy a bag of shear pins and replace them as they break than to have to replace some more critical parts.

[@GuitarSamurai17]

brilliant! always love learning from you!

[@xsauce3858]

awesome little video...got smarter thats for sure

[@Joelasagangsta28]

I just learned something new. Thanks, as always, Destin!

[@aviationyyz4679]

You can find the same thing on aircraft landing gears. There is a fuse pin which is designed to be the weakest part and will shear during certain ultimate loading conditions. This allows the gear to nicely fold away rather than go through the fuselage during an extreme hard landing.

[@rushwal]

On a recent boating trip, two of the guys had shear pins save their outboards. one even brought the piece of wood back with him. 😀 Shear pins work!

[@KjKase]

The extra little bit about starter gears having softer teeth than flywheels was interesting; I did not know that, thanks!

[@gephc4]

At my old job, we would repair industrial centrifuges. One of them came in with a completely mangled up gear box. It was a total loss. Someone decided they could replace their busted shear pin with something a bit stronger. I bet they felt pretty clever for about 10 minutes.

[@SimKiller09]

This is interesting! I'm used to working with rupture discs on pressurized vessels, but never occurred to me gears would have a similar failure design. Thanks for posting! =)

[@mbrsart]

We went through a bunch of shear pins on our auger when we were drilling for the wooden posts for our stalls. Super rocky ground, lots of binding up.

[@travisscavoni369]

Actually learned something here. I always lumped these together with cotter pins, and never knew there was an actual difference

[@Pete856]

And I just learnt something too, from your reply. I always thought a cotter pin was just another name for a split pin, but your reply made me google other uses for that word. Turns out a tight fitting pin or wedge connecting two parts is also known as a cotter pin....who know? BTW, what Destin calls a "shear pin", we call "shear bolts" because it's a bolt and not a pin :)

[@Geeksmithing]

nice Destin! Please do more like this

[@jimroberson9534]

Gear teeth are hardly ever something that are designed to break, from my experience that is what keys sitting in keyseats on shafts and keyways in gears are for; a weak shear point to protect the gear teeth. You described shear pins perfectly. Love all your videos Destin.

[@mecengme4900]

I have come across to shear bolts when working at the airport where they are used with the aircraft towbars. If the pushback tractor for some reason stops quickly or something else happens the shear bolt breaks and disconnects the towbar and pushback tractor from the aircraft front wheel without damaging the landing gear. For some reason this happens quite a lot with some aircraft types and we haven't figured out why. Some other aircraft types work fine and the shear bolts don't usually break without a good reason.

[@billd66]

Kitchen Aid stand mixers have a single plastic gear in an otherwise all metal drivetrain. It's intended to strip in the event the beaters hit something hard and stop. The plastic gear is easy to replace and protects the rest of the gears and the motor in case you dump a bunch of gravel in the bowl or something.

[@Sierra_Victor]

A lot easier to replace a small, cheap bolt than all those internal and expensive mower assemblies.

[@spikeman4pres]

Thats freakin awesome, i just finished my mechanical design class and this is the type of stuff they were teaching us

[@IMMORTALone84]

Wow, I never thought of it like a fuse. We had a double feed in one of our M61A1 guns and the pressure sheared the bolts right down the middle of the system. Makes me wonder if this was a shear pin/break-away design or the force was just that great...

[@numbskull9942]

In Germany we have a extra word for it "Sollbruchstelle"

[@gitarhiro]

beat me to it

[@numbskull9942]

Adam Moore yeah i know it's right ;P the words translatet mean something like "shouldbreakespot"

[@vin_2620]

Of course there's a word for it German 😁

[@Jookyforever]

This is also done in seismic building design a lot. For instance some removable/replaceable sections in eccentrically braced frames or for a longer time "dog bone" cuts in steel beam flanges.

[@alancoe5814]

Super helpful. Thanks for making this.

[@deathfear8175]

That's why we have a whole box of them laying around or farm because if your running the baler and the hay is slightly wet your gonna shear a couple and you don't want to have to run to town every time it happens

[@SeanBZA]

With the failsafe you also had a safety feature, the drive shaft is keyed and socketed, so it does not flail around on shearing the pin, but safely runs free. Also the shear pins on trailers are backed up by a chain so the trailer can be stopped safely. The tractor also has safety in the lift for the mower, the power in the hydraulic cylinders cannot deliver enough power to break anything before the relief valve limits pressure in the system. Further to that if the safety pin is replaced with the wrong bolt ( or welded up by some fool) the gearbox on the mower side is weaker than the PTO side, and will fail first, and same with the cheaper PTO as it is weaker than the drive side gearing. The universal joints are a weak spot, but are designed so the gearbox will fail first, unless you ignore the joints and do not service and examine them.

[@BubbaGooder]

Yep, that's a handy dandy safety feature! Thanks for the quick and simple explanation

[@joejoseph1593]

Sometimes the shaft is necked (reduced in diameter) to act as a mechanical fuse. Great stuff you post man. Mechanical engineers rock :P

[@bleepinjeep]

First Chucke2009, now smartereveryday? Everyone is turning into farmers!

[@joshkahn9600]

Thanks for teaching us that one and Happy Father's Day Destin.

[@TheLordReverend]

cool stuff Dez!

[@T4nm4y]

We actually just recently learnt about this! :P

[@ZukaroTravon]

I love things like this. 'w' I actually used to do stuff kinda like that in Robocraft back when the damage system was different (design things so when my bot was shot certain parts were more likely to break than others (obviously, a lot different than this, but a similar idea, designing things to fail in a certain way)).

[@Axelm15]

very very smart solution! thanks Destin

[@reggieasplund9081]

My Heidelberg Windmill printing press has one of these to keep the press from jamming, such an incredibly clever way to keep damage from happening to the important parts.

[@ABLovescrafting]

That's awesome! Thanks for sharing!

[@deankruse8751]

ny neighbor has a tractor inplement that is a sickle bar mower and the main transfer of power from the pto to the cutter is through what looks like a 2x2 chunk of wood. it the same kind of mechanical fuse that breaks easily and is easily replaced

[@alainvaudou]

Those are handy, Same as snowblowers shearpin for the front auger/differential. Works the same !!! it cost so much less to replace 2 bolts than to replace an whole gearbox !

[@Acidicheartburn]

You'll find these on snowblowers. If a rock gets in the auger and stops it the shear pin should break and save your snowblower. Also helps make it safer to get the rock out of the auger, since it can prevent the system from binding up with a bunch of spring mechanical potential energy that could release suddenly and dangerously.

[@PearseSmyth]

They've saved me more times than I'd like to admit. Great wording of what they are. Will deffo use mechanical fuse to describe them to non farmers again.

[@trentraymond9359]

Hope you got something to eat along the way home. #StomachGrowl @ 1:25

[@SmarterEveryDay2]

+Trent Raymond I was hungry

[@Goretantath]

Smarter Every Day 2 was working up an apitite xd

[@jakthesmack]

The fuse analogy is actually really good. You need to choose of the right size for the job. Too small and you pointlessly limit the amount of work you can do, too big and you risk damaging the more important parts of the system if something goes wrong. Thumbs up, great clip.

[@user32455]

More videos like this please

[@williamtylerast]

very informative. i never thought of soft bits of cars, bikes, and other gear as mechanical failpoints. not that all of them are - but it'll be interesting to ask myself that anytime i run into a soft part that i think is just poorly built when in reality probably saved me a ton of hassle elsewhere.

[@TheeBadAndy]

Destin, love you videos, I get excited when I see there's a new video from you. Can I offer a little piece of advice? You obviously like to work with your hands a lot. I'm a medic and I see dozens of injuries involving the hands. One of the most preventable of those involve wedding band injuries. I love my wife more than anything but I stopped wearing my ring years ago. I suggest one of those rubber/nylon bands or what I did😯tattooed mine on. Just looking out for you. Keep the vids coming.

[@Physhi]

Destin! I am hoping you are dragging Brady along with you for the eclipse because of his expertise! Personally I'm having a time trying to convince my family to go and see it. Much love from a Texan boy!

[@Sonic10Inu]

Cool. Thanks for teaching us something new.

[@Anehab100]

that's very dad like of him. "hey son, since I have some time, let me teach you about shear pins! well you see..."

[@TheWireEDM]

Bonus points for the engineer who designed it to use a regular bolt of some grade and not a part that has to eb special ordered and will take 5 weeks to get if even available after 2 years of purchase.

[@apk493]

I actually just started working on the ramp at my local airport, and the towbars we use to push back the planes have the same thing! It's legit exactly like you described, except in our case, it's so we break the towbar before we break the nose landing gear on a plane :P

[@WorthySK1LLZ]

they use those shear pins in car washes to!

[@BrendanOrr]

You know, I was wondering about that some days ago. "What if one of those strips of cloth caught on my rusty undercarriage?" Assuming the strips are strong enough to not rip apart themselves.

[@WorthySK1LLZ]

Brendan Orr they do rip on there own. but if the sensors or programming malfunctions on the carwash and the brush tries to hit your car too hard the shear pins break to keep it from damaging your car

[@EclecticBuddha]

Also used on railroad crossing type gates so if it comes down on a vehicle inadvertently, it limits damage to the car. Small gates use nylon bolts.

[@charlotte1924]

That is very smart! Thank You and happy fathers day (in England)!

[@emtffzartman666]

Snow blowers also implement these in many cases. Same theory, but also to cover someone placing their hand inside.

[@Ke3per88]

These things are a godsend on outboard engines. Always keep 2-3 spares inside the housing.

[@connorwelch9632]

I saw this on your Snapchat yesterday!

[@sachiperez]

i predict this will be one of your higher rated videos.

[@SmarterEveryDay2]

+Sachi Perez why is it so interesting?

[@jawms]

Dad always referred to that piece of kit as a "Texas Lawn Mower" but I guess Bush Hog works as well..

[@phooogle]

THANKS DESTIN :)

[@viveksoley]

mechanical fuse ... perfect formulation of words

[@RENWTERVD]

pls make more videos like this, i want to know more XD

[@jimday666]

predetermined weakpoints are a must almost in every system

[@powwow151]

One of the most commone questions when I worked at a hobby shop was what they can upgrade the plastic spur gear up to so it won't break. had to explain that a 3 dollar gear is a lot easier to replace than a 40 dollar motor and it was actually designed that way

If life gives you busted tractors make lemonade.

[@siggyincr7447]

Never seen that system before. The ones I'm familiar with have a clutch pack in the drive shaft to allow slippage if the torque goes too high.

[@BushPigADV]

Happy Father's day! A buddy of mine replaced a bunch of shear pins with grade 8 bolts because they "kept breaking". Needless to say, he snowblower didn't make it through the winter.

[@danphillips8530]

Yea, I also like the shear pins on lawn mowers as well, instead of breaking something internal when you hit something it shears the pin on the fly wheel.