(warm twangy music) - This piece of metal is an
offcut from a machine shop. There doesn't seem to be
anything unusual about it until I push this piece out. How amazing is that? Until the part is pushed out, it's as though there is no seam at all. Look at this one. This is called a MetMo cube. What's cool about this is
there are actually two parts that slide in and out, and internally they're
connected via a small borehole. So when you push one of them
down, the other one pops up. It's very satisfying. But like, how on earth is
one of these things made? How can there be almost
no discernible seam between these parts? Well, these curiosities are made with a technique called wire EDM, or wire electrical discharge machining. Wire EDM is used for all
sorts of useful things. These curiosities aren't useful as such, but they're a good way to demonstrate the ridiculous precision of wire EDM. You may have seen other
examples of this online. When I did, I became obsessed with figuring out how it was made and more importantly getting hold of one. There are actually a couple
of really clever tricks involved in the manufacture
of these invisible seams. Like when I heard that these were made by a process called wire EDM, I immediately got distracted by what I assumed that must mean. I just thought, "Oh, right,
it's like a cheese wire." If you want to cut a circular hole, then you drag the wire
across into the cheese, cut the circle, and then
carefully pull the wire out. Or if you don't want this cut here, you first drill a hole in the cheese, we've all done it, feed the wire through, reattach
it, and then do the cut. Another good analogy analogy is cutting styrofoam with a hot wire. The wire melts the styrofoam. It's quite therapeutic, actually. There's a problem, though. You either need to have a cut in this part or a cut and a drill hole in this part, but neither of these
seem to have those cuts. Also, look how much wriggle
room there is there. That's at least half a millimeter. Whereas here, there appears
to be no apparent clearance. Like, how thin is this flipping wire? And actually that's the first trick. This is actually made from
two separate bits of metal. First you cut the hole, then separately you cut the
part that goes into the hole. And you just have to make sure that you compensate for
the thickness of the wire so that when one part
slides into the other, it's a nice snug fit. And actually, that's something
we can see with this part because the piston was
actually cut from over here. And if I put that piece back
to where it was cut from, you can see the wriggle room. Measuring with calipers, it's about 0.2 millimeters
all the way around. That's consistent with
the width of the wire. And look, there's that
unavoidable cut line. I managed to do the same thing
with the cheese, actually. Fits perfectly. Now, what about this second trick? Well, we'll get to that in a moment, but first how does wire EDM work? I went to a machine shop called Travelling Wire in
West Sussex to find out. So this machine does EDM without a wire, and it's a bit easier to see
what's going on, actually. So this is the part and this is the tool that's
going to cut into the part, except it's not cutting
in the normal sense. The way it works is you
put a really high voltage between the tool and the part so that if there were to touch, it would complete the circuit. But in reality, the voltage is so high that the part and the tool
wouldn't need to touch. They would only need to get close enough for a spark to jump from one to the other. And every time the spark jumps, it erodes the surface
of the part slightly. For the purposes of EDM though, you don't allow the spark
to travel through air. Instead you surround the part and the tool with an insulating liquid. The liquid has well controlled properties so it breaks down at predictable
voltages and distances. It's also a better heat sink than air, keeping the bulk of the part
cool to prevent expansion. Why doesn't an electrical spark erode a contact point though? Well, interestingly,
we don't know for sure. One impossible explanation is heat. When there's a spark, a huge
amount of electrical energy is converted into heat energy in a very short period of time, so the metal gets very hot, very briefly. And some of those metal atoms will vaporize away from the surface. So if you want to etch away at something, this is the tool for you. But if you want to
slice through something, you need a different tool. That's where wire EDM comes in. This is one of Travelling
Wire's wire EDM machines. By the way, check out the
link to Travelling Wire in the description for
all your wire EDM needs. They're not paying me to say that. So we want to cut out a little bit of this sheet of metal here. There's already a hole in the middle so we can feed the wire through there. This jet of water helps to guide the wire as it's being fed in, and once it's through the hole, some machinery underneath grabs it. The whole thing is then
submerged in water. Actually, water is only
a good insulating liquid if it's free of ions, so this water is deionized. There's a machine around the back that takes tap water
and this special resin. It does something with it and
pumps out deionized water. Unfortunately, once the
sides of the tank are up and the thing's filled with water, you really can't see what's going on. Not that it matters when you've got a
brilliant cheese analogy. One big difference between the
cheese wire and the EDM wire is that the EDM wire is constantly moving. These pulleys are constantly turning, and if we go around the back you can see it's being
chopped up and spat out. That's because the wire itself erodes as well as the part you're machining. This spool here contains about
10 kilometers of brass wire. And look, there's the part now, cut out exactly how Richard here drew it in his CAD software. You can also angle the wire in clever ways so you can cut tapered parts and holes that have a
different shape at the opening than they do at the end. You can do all sorts of
cool stuff with wire EDM. But what about that second trick? Well, look, here's the
first part that I showed you when it's halfway through
the manufacturing process. The piston is already cut
out and it fits perfectly. But look, because it was cut from a different part of the metal, you can see it, right? You can see that it's a
different piece of metal. So the final trick is to
polish, or grind, really, the two parts together in situ. By grinding the two parts
together in this way, they obtain a matching finish. The grain of the abrasion
pattern flows seamlessly across the seam. And so it seems as though
the seam can't be seen. And look, you can achieve
the same thing with cheese. Even knowing how this is done, the precision is unbelievable. A typical wire EDM machine
will have a precision of around 5000ths of a millimeter, which in inches is a different number. Why is wire EDM so precise? Well, it's mainly because the
tool and the part never touch so they don't perturb
each other in the same way that you get with an abrading tool. So there you go, wire EDM. The mechanism that joins
this thing to this thing is really clever but not in
the way that you might think, and actually not in a good way. In fact, it's in an evil way. Let me explain. The mechanism is just complicated enough and just novel enough to be patentable. That means no other manufacturer is allowed to make blade cartridges that go with this handle, which means if you buy this
handle you can only buy blades from the same manufacturer at a significantly inflated price. The same thing is true for
single use coffee pods. The same thing is true for the heads of electric toothbrushes. And amazingly, the same thing
is true for the uranium rods that go into certain nuclear power plants. Like, wouldn't it be nice if you could just pay a reasonable price for your nuclear power plant? And then you get to buy the uranium rods from wherever you like. Wait, sorry. I mean, wouldn't it be nice if you could pay a reasonable price for a really well-engineered
razor blade handle, and then you get to buy the
blades from wherever you like? And actually, even the really good quality
ones are just pennies. And that's the idea behind Henson Shaving, the sponsor of this video. The Henson AL13 is what you get when a family-run aerospace machine shop pivots to making its own products. Its CNC machines to aerospace standards, and because it's all metal,
the blades are well supported, unlike the multi-blade
plastic cartridge razors. And it's just nice to own something that's well made that you're
gonna make good use of, nevermind the fact that
the total cost of ownership would easily be cartridge
razors after only a few months. But what's it like to use? Well, I shaved this side of
my face with the Henson AL13 and I shaved this side of my face with the leading cartridge brand, and the difference is remarkable. Go to hensonshaving.com/stevemould and use promo code STEVEMOULD at checkout to get 100 free blades with
your purchase of a razor. Just make sure both
products are in the basket when you apply the code. The link is also in the description, so get yourself a precision
engineered safety razor today. I hope you enjoyed this video. If you did, don't forget to hit Subscribe. And the algorithm thinks
you'll enjoy this video next. (upbeat music)
