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We have all been there, visiting your local hardware store like a kid in a candy shop.
You arrive at the pick and mix screw section and you are just overcome with excitement.
How could you possibly pick just one type of screw.
Woooooow look at all these screws.
Amaaaazing.
You have sultry slotted screws, rowdy robertsons, playful phillips, oh and look at this one
a hex screw.
You naughty polygon.
In your excitement you pick the largest bag you can find and fulfill your childhood dreams
to buy 2 of every kind of screw.
Mother can’t stop you now.
You arrive home with the glee of a spring lamb.
Oh the assembly that awaits.
What joy.
Then, to your horror, you open your toolbox to discover you only have a fat flat head
screwdriver that doesn’t even fit the flat head screws your bought.
Your life is a lie.
You spent your life studying theory and never learned practical application.
You are no real engineer.
Shhh it’s all going to be okay, dry those existential crisis tears.
We are going to learn what all these screws are for, and how they came into existence.
The humble screw is a technology so old that we cannot easily determine who first invented
it, but the answer as best we can tell is Archimedes who used the helical screws ability
to turn rotational motion into linear force to pump water, though he probably stole the
idea from the Egyptians.
You can imagine how a screw works fairly simply by viewing the cross-section at the bottom.
This part is essentially a wedge, and when you force a wedge under something it will
lift it up.
This wedge shape spirals all the way up the screw, allowing that force to be applied along
the full length of the screw.
This idea was used for centuries to pump water, dig holes, and for pressing the shit out of
grapes to make some wine.
Then some unknown person had a bright idea.
If we can apply an opposing force, we could create compression to hold two parts together,
and so someone slapped a head on one of these screws that would press down while the threads
pulled upwards.
Creating an incredibly useful fastener.
This idea didn’t really take off until a method of mass manufacturing them came about
in 1797, when Henry Maudsley invented this metal cutting lathe that allowed for the consistent
and precise cutting of screw threads.
He even set up a standard screw thread geometry for his machine shop , and cut all his nuts
and bolts to fit those threads, and thus the chaos started.
Several decades of differing standards resulted in headaches far worse that your annoyance
at new phone not fitting your old charging dock.
Perhaps the most notable incompatibility occured during the great boston fire of 1872 when
fire departments from neighbouring regions arrived to help, only to discoverer their
fire hoses didn’t fit Boston’s fire hydrants.
[Maybe show XKCD comic]
Most of the world has now accepted ISO metric threads as a standard, although one country
is still holding onto the inch as the standard unit of measurement.
A measurement that was legally defined as the length of “three grains of barley, dry
and round, placed end to end, lengthwise” for 8 centuries until it was redefined as
25.4 millimetres.
Because, as we all know, the best in class is always defined by the second best, but
I digress.
We can now generally trust that a nut and bolt with the same diameters will fit, even
when mixing freedom units and metric, but what’s the story with all these different
screw heads.
Why can’t we just agree on one shape so we don’t need a toolbox full of screw drivers?
The simple slotted screw head was likely the first type used as it’s easy and cheap to
manufacture with a cutting tool, but is a pretty terrible design for anything other
than manual screw driving into wood.
Screwdrivers can slip out of sides and you can turn the screw off its centre axis, which
causes it drive into the material at an angle.
This was not acceptable for mass production methods, which as we explored previously,
needed a foolproof production method.
So Peter Lymburner Robertson designed a manufacturing process for this square bit screw-head.
Which was designed to be easily and quickly driven home, without danger of the screwdriver
slipping out and damaging either the screw of the workpiece.
700 of these bad boys were used in the Model T, and it saved Henry Ford about 2 hours of
manufacturing time on each and every vehicle.
Henry Ford was so happy with the design that he wanted to licence it and manufacture them
himself to ensure he had a reliable and steady supply of the fastener, but Robertson wasn’t
about that money making life and said no.
He continued doing this with other manufacturers for some bizarre reason and now the design
is mostly just used in Canada, and so in stepped Henry F Phillips with his infuriating screw
design.
He licensed out the design to Henry Ford and many other people.
This conical cross design allowed for a single screw driver to fit many sizes of screws,
was self-centering, and was designed to cause the screwdriver to slip out of the slot at
a certain torque and thus prevent workers from over tightening it and damage the screwdriver
or workpiece.
It also prevents you from getting the blasted thing out of a workpiece with even the slight
bit of rust.
By 1939 this design was licenced to nearly every automotive, airplane and rail manufacturer
in the US, just in time for the boom in manufacturing created by World War 2 [1] With the lend lease
act, many American designs were sold to their Allies, and thus the screw design spread even
further.
Now that most screwdrivers can automatically limit torque the phillips design is pretty
much just a pain in the ass, so other designs have come to the fore in more recent years.
Specifically designed to stop that slipping called cam-out, like hex screws and torx screws.
Let’s compare these two types of screw to see how their design came into existence.
These two screws have the same diameter tool.
Both have six points of contact between the screw and tool.
However we can see when we rotate our hex tool it contacts the screw at a greater radius.
Allowing it to applying more torque with the same force, but the plane of contact is not
perpendicular to the circle and that means some of the force from the rotation of the
screwdriver is being applied outwards radially to the screw.
This can damage both tools.
With the torx screwhead the angle of contact is near perpendicular, meaning it can applied
more torque without fear of damaging the screw.
But ironically, even though this is a great screwhead design.
It was designed to not be used by the general populace.
It was used in Apple’s first personal computer [2] to make it harder for the average guy
with a phillips head screwdriver from opening up the machine.
But thanks to it’s design, Torx screws started proliferating, and more and more people had
the correct tool to loosen it.
So someone decided to place a pin in the middle to make it even harder.
Bringing us to an age where our right to repair is questioned and many random screw designs
have appeared to make it harder for us to take apart our gadgets . Why?
Because screw you that’s why.
If all these nuts are driving you crazy, you might just be a squirrel and being a worldly
squirrel you probably learn about all the other types of squirrels around the world.
There’s ones with wings, ones with cute little ears and tails.
Look at this ginger one, class.
If you want to learn more about them.
I highly recommend watching this documentary titled “Going Nuts” on curiositystream.
It’s a beautifully shot documentary that I really enjoyed.
For a slightly more on-brand recommendation, they also have an exclusive, original documentary
series premiering on the 13th of June about the new race to the moon called ‘Return
to the Moon’.
You can watch it for free, by signing up to curiositystream using the code realengineering,
or using the link the description.
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