- Engine bolts, lug nuts, even your oil cap
has a specific torque spec from the factory.
Sometimes, you just got no time
or you got no patience or you got no torque wrench.
And you just want to take your own air gun,
it down to snug as you can get it.
But why is putting a nut on
as tight as you can go a bad thing?
Why do we even have torque specs in the first place?
And what would happen if we tried
to tighten a bolt with a 13 foot breaker bar?
(beep) This is crazy, man.
Well today's video, we are going
to show you exactly what is happening inside a bolt,
as it gets over torqued.
We are also going to set up an experiment
to see if we can replicate our research.
So sit back and enjoy as we get down
to the nuts and bolts of torques spec.
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of bumper to bumper.
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What are you guys waiting for?
Now let's get back to some B2B.
Don't worry, the car's not on fire,
this is practical effects.
Welcome to Donut, baby.
(laughs)
(beep)
Torque spec is the measurement of a force
a given nut or bolt is designed to be used at.
It's tight enough to hold the bolt in place,
but not too tight so that
it damages anything, including itself.
And if we keep on turning that nut, however,
a combination of things are going to happen.
The bolt will break, like we've seen.
The metal clamped in between your nut
and your bolt, it's going to buckle, it's going to squish
or the bolt will permanently deform.
Now the strength of a bolt is known as tensile strength.
And this is the amount of tension
the bolt can withstand without being fractured.
Now, if you multiply this by the surface area
that tension is being applied to,
you can get the tensile load
that you're going to apply to the bolt.
So as bolts get more and more tension put on it,
there comes a point called yield point.
And this is the amount of tension
that it takes to permanently deform a bolt.
Everything below this point, is called the elastic range
and everything above this point,
is called the plastic range.
Now, when you apply a load to a bolt in the elastic range,
and then take away that load,
the material goes back to normal.
The molecules that make up whatever material stretching,
they snap back, like elastic pants.
Just think of that, that'll make you remember that.
But when you apply a force that gets into the plastic range
and then take off the load once again,
the material, it doesn't snap back.
Those molecules are permanently broken
and the material has undergone,
what's called plastic deformation.
Now torque spec is often 70 to 95% of this yield point,
depending on the application,
so it's in that elastic range.
After the yield point,
the bolt hasn't necessarily failed though.
In fact, you may have heard of TTY
or torque to yield bolts.
Beyond the yield point, the bolt can still
be stretched a bit and hold up to higher tensile load.
But eventually, that tensile strength will plateau
and then start to drop off.
And that's the point where you break a bolt.
Now imagine a spring, now you can compress it,
just a little bit, or you can pull it a little bit,
but if you pull too far,
it's going to permanently deform,
and it won't go back to its nice springy self,
even though you didn't actually snap it.
That's plastic defamation.
Shout out to every 90's kid,
who broke a slinky that way.
So to show you this, we've set up a few experiments outside.
We're going to use my F150 as a test rig.
How I got suckered into this, I don't know,
but let's go to outside Jerry and see what he's doing.
Thanks to inside Jerry.
So we're going to put some of this stuff to the test.
We got a rig that we built up on the back of my F-150, here.
We have an extender coming out of the hitch
and through that extender, we have a bolt.
And what we're going to do,
is we're going to start off by torquing
that bolt to 40 foot pounds
and work our way up, all the way to 150 foot pounds.
And my buddy here, Joe,
he's going to be measuring bolt length changes
as we go up, and over torque this bolt.
And then, we're going to use this big old honker,
to see if we can actually get enough torque to snap an...
- [Robotic voiceover] One inch thick
- Bolt. We also bought a 13 foot stainless pole
to give us a little bit more leverage
to see if we can use math, to make it happen.
And if not, we'll just use these guns.
- We're gonna use the math.
So what I'm doing now, is I'm measuring our bolt
to see how long it is before we put it under tension.
So that when it stretches, when we do torque it to spec,
we can see how much it's stretched by.
- Now we tested several different types of bolts
at varying degrees of torque.
And what we found was that our three and a half inch bolts
would stretch about half a millimeter
at 120 pound feet of torque.
Now, when we undid those bolts,
they sprung back to their original length.
Now this is a bolt that is torqued down properly.
It's got enough stretch,
that the elastic tension clamps the assembly together,
but it still remains true to its original shape,
when the bolt tension is loosened.
Now we tried this experiment again with thinner bolts
to see if we could really show the bolts stretching,
but you know, these freaking guns of mine showed up
to do some damage and well, we rig him, we broke it.
(metal clanking)
That's called snapping off the bolt, baby.
(upbeat music)
So we were able to snap this 1/4 inch bolt,
with around 140 foot pounds of torque.
So that means to snap this one inch shank ball,
we need around four times as much, right Joe.
- Yeah, maybe. Let's see.
- Now this is a one inch shank ball,
it's course thread, SAE grade five.
So we're going to put about 600 foot pounds of torque using
this nice little rig that Joe rigged up,
is a breaker bar with a 13 foot stainless steel pole.
We're gonna hang sand bags on the end of it
and see if it can snap this.
So right now we have 182 foot pounds of torque
on this bolt right here.
That's factoring in,
the weight of this 13 foot stainless steel pole.
And the first sand bag Joe
is going to put on, is 35 pounds.
And we're going to keep adding bags from there
to see what happens.
- Alright, let's do it.
- Let's go.
Do you need a ladder?
- A ratcheting wrench won't work for this,
so we got to bust out a ladder
to get this bar on the breaker bar.
- So that's about 600 foot pounds of torque
on that bolt right there.
So now we're going to add another 25 pound sandbag.
See if it bends it even more.
- Six that we're adding, comes down, so this is 800.
And this is about 900 foot pounds.
- This stressful.
Do you guys really want to keep going.
- I've got the hook, Yeah.
Alright. This is now getting like hard for me to move.
- Damn, look at that pole bend.
I don't want to be anywhere near.
- Nope. Hold on.
That's good.
(laughs)
This is like the worst game of Jenga.
- This is the worst, I say, we're done, dude.
- (laughs). - This is crazy, man.
So we put over a thousand foot pounds of torque
and it didn't shear. So what gives?
Did our math fail us?
Joe, is it your fault?
- You know what?
I can't put any more torque on this.
- So why did a bolt, four times the size
of the little bitty experiment bolts not break
with four times or heck even seven times the force.
Well, let me explain.
And when you're buying bolts, they're measured in diameter.
And diameter, that's a one dimensional measurement
and to calculate tensile strength,
we got to use a two-dimensional measure.
A one inch diameter circle
is 16 times the area of a quarter inch diameter circle.
So we would have needed over 2200 pound feet of torque
to break that bolt.
But the math, it doesn't end there,
because the area we need to use for the calculation,
isn't the flat end of the bolt.
It's the area of the surface area of the threads.
And that area is partially determined
by the thickness of the bolt,
but it's also determined by the thread pitch and depth.
So with the larger bolt, you also have a larger nut
and the amount of threads contacting within
that nut increases the surface area
of threads touching and spreading out that force.
So even a minor increase in bolt diameter, thread length,
or thread pitch can really change
the amount of torque a bolt can take.
Because of this, one of the big things
that can really become a problem
with torquing down bolts, are contaminants.
Now threads, if they're dirty, if they got grit in them,
they got metal shavings or even surface rust,
that can change the amount of surface area making contact
and lower the failure point of the bolt.
Also the amount of force needed
to break up some of those contaminants can lead
to a false reading on a torque wrench.
I'm sure some of you guys may have heard the term,
dry torque and that refers to the torque applied
without lubricant, because lowering the friction
that comes with lubrication can also throw off torque.
So if you're a whiz boy,
or you're whiz girl watching this show,
you can see by just using a torque wrench,
you can get an unreliable measurement.
And that's because, torque is the measurement
of turning force applied to a bolt,
not the amount of tension in the bolt itself,
but unfortunately there's no cheap or easy way
to measure the actual tension in a bolt.
So torque is the only number we've got to rely on,
but because of this, there's another technique out there
that makes torquing down fasteners
to perfect spec, super duper easy.
It's called the torque and angle technique,
and here is how it works.
Instead of just the measurement in pound feet.
You have a measurement and an angle.
So if your torque spec is 30 pound feet at 90 degrees,
you torque your bolt down to 30 pound feet,
and then you'd give it a quarter turn.
Why are quarter term?
Well, every 360 degrees of rotation of the bolt,
the nut moves down the thread by fixed amount.
This is called the thread pitch.
So when you start off with
a lower torque value, snug torque, every degree of rotation
after this will be used to stretch that bolt.
Because no matter what, that quarter turn is going to move
that bolt down the same amount of thread every single time.
So this pretty much eliminates the fact
that variations in friction have
on the torquing process compared
to when you're just using a torque value on its own.
And if you want to see bolts, get expertly torqued
by Mr. Zack Joe, go check out our series, Money Pit.
If you want to see some behind the scenes footage
of all the stuff we can't include in this episode,
because we're very serious in B2B,
but sometimes we do a lot of goofy things
that you don't get to see.
Go hit that join button down there
and be a part of the Donut underground.
Follow me on Instagram, @jeremiahburton.
Follow us on Donut, @donutmedia.
Until next week, bye for now.