28x03 - Angle Grinders, Berry Baskets, and Omnidirectional Speakers

[bunniefuu]

Narrator: the angle grinder
created a major buzz

In the workplace
when it was developed

In the middle
of the 20th century.

This power tool
could do it all --

Cut, grind, and polish
metal or stone.

Just change the disk
or brush attachment

To match the job,

And work gets done
automatically.

With numerous
attachments available,

The angle grinder

Could be equipped
for many different jobs.

That makes it one
of the most useful things

On any job site.

Making angle grinders starts

With these blocks
of pure aluminum.

Fired in a furnace,

The aluminum melts
into a liquid form.

The factory casts
the molten aluminum

To create gear housings.

A robot transfers
one of the gear housings

To a milling station

And then retrieves
a finished part.

The door of the machine closes,

And a computerized cutter
carves threads

Into the center bearing seat

And generally improves
the profile of the part.

Next up is the rotor
for the electric motor.

An automated system pushes
special cardboard end disks

Onto the rotor shaft.

The part on the right
is equipped with end disks.

The system now installs a part

Called the collector on one end.

Made of copper and plastic,

The collector will transmit
power to the rotor

And ensure that the grinding
or polishing attachment

Can turn.

The part on the right
has had the collector installed.

Spinning arms wind copper wire

Into grooves in the rotor
at both ends.

The wire will serve
as an electromagnet

And maximize power output.

Moving forward,
the system inserts covers

Into slots in the rotor wall.

They both insulate the rotor

And stabilize the copper coil.

Spinning devices
wrap copper wire

Around each half of the stater.

This stater creates
the electromagnetic field

Around the rotor.

A robot puts the two halves

Of the stater
together in a fixture,

And welds make
the assembly permanent.

Over to an injection
molding machine now,

It forms plastic into outer
casings for the grinder.

A robot transfers the casing
to a platform for printing.

This stamp adds silver ink
to the embossed company logo,

Giving it greater visual appeal.

A worker then slides the plastic
housing over the stater,

And a pneumatic machine
press-fits the two together.

The worker then wires
the on/off switch

For the angle grinder.

The gear housing has,
by now, been equipped

With a drive gear and brake.

He installs the gear system
on one end of the rotor.

He then inserts the rotor
assembly in the stater.

An automated system
screws everything together

To complete
the angle grinder motor.

Next, a nozzle fills
the gear head with grease.

A worker places the spindle

And safety clutch
over the gear head,

And a mechanized system
screws it in place.

She then wires
the electrical plug

To the angle grinder motor.

She encloses the electrical
wiring with a plastic cover.

She locks the cover
in places with screws,

Using a metal template
to aid in their placement.

This angle grinder

Is now ready to undergo
quality control tests.

This one depresses
the angle grinder switch,

While a computerized system

Analyzes the motor's
performance.

If it passes all the tests,

The angle grinder
is ready to take a chunk

Out of someone's workload.

Narrator: long before
the development of pottery,

People looked to the forest
for containment materials.

They made berry baskets
from the bark of birch trees.

The baskets were
lightweight and waterproof,

Due to natural
resins in the bark.

The making of these baskets

Is a tradition that carries on.

For containing nature's bounty,

Birch bark is a natural choice.

This berry basket
is made entirely

From materials found in nature.

Making one starts
with birch bark

That's been carefully
pried off the tree

To avoid damage
to the inner layer of bark.

This cardboard pattern
will be used as a template.

The basket maker
examines the bark

For any holes or serious flaws.

He flips the bark over.

He'll use the inner side
for the outside of the basket.

He traces around the pattern,

Using a scribe that
lightly scores the bark.

This light scoring creates
a visible outline on the bark.

Using scissors
for cutting leather,

He follows the pattern lines

To cut the bark
to the pattern shape.

The contours
are harder to follow,

So he switches to scissors

With curved blades
to cut them out.

He punches holes
in the basket corners.

This will stop the bark
from splitting in these spots

When it's folded.

Using a pointed instrument
known as a divider,

He now etches stitch lines
around the perimeter.

He maps out the location
for the stitch holes

By lightly piercing the bark
along the etched lines.

Using a ruler for support,

He bends the flaps
of the pattern up,

Creating creases that will
become permanent folds later.

He punches out stitch holes

Where he had lightly
pierced the bark.

He drapes a damp towel
over the birch bark

And irons it.

This softens the bark
so that it doesn't split

As he now forms the final bends
along the crease lines.

He overlaps the ends
of the basket.

He clips the structure
to hold it together

While he inserts wooden dowels
in some of the stitch holes.

Once the dowels are in,
he removes the clips.

The dowels will keep the basket
together for stitching.

But first, he tapers the stem

From a willow shrub
using a wood plane.

He inserts the stem
in a cylindrical container

And fills the cylinder
with hot water.

The tapered stem
soaks overnight.

It softens and becomes
extremely flexible.

Using a wooden form,
he shapes the stem into a ring.

The tapered ends overlap
for a consistent thickness

All the way around.

He clips the ring
to the inner rim of the basket

And also tacks it in place
with a few stitches.

This willow ring
will add support

To the lip of the berry basket.

Next, he stitches
the seams together

Using the root of a spruce tree
for thread.

Its tapered tip serves
as a needle.

He does precise backstitches

And ensures all
the seams are tight.

Moving back to the rim
of the basket,

He punctures the bark
just below the willow ring,

Creating a row of holes

To loop the root
around the rim.

This spruce root wrap
protects the rim ring,

And gives the basket
a more finished look at the top.

He slices a piece of cedar bark

Into long, narrow strips.

He'll use these strips to make
a handle for the basket.

He weaves the cedar
into a five-strand braid.

He loops the cedar
braid at the ends

And uses the loops
to stitch the handle

To the berry basket.

It takes this artisan
about a day

To craft a birch bark
berry basket.

His efforts will no doubt

Bear fruit
for many years to come.

Narrator: choosing the right
speakers for your sound system

Depends on how you prefer
to hear music.

Unidirectional speakers radiate
sound in a single direction.

Omnidirectional speakers radiate
in all directions,

So the sound bounces
off the ceiling and walls.

This omnidirectional speaker
system has four towers --

Two main system towers
and two subwoofer towers.

The towers contain the drivers

That radiate sound frequencies
out of the speaker.

This computer-guided mill
shapes brass sheets

Into mounting plates
for the main system towers.

Each of the main system towers
contains six drivers --

Two tweeters, two mid-ranges,
and two woofers.

Each subwoofer tower
contains six drivers

For the lowest human
audible frequencies.

After the brass mounting plate
comes off the mill,

Workers grind
the top surface smooth

To prepare it for polishing
and chrome plating.

The mill then
shapes brass rings.

These are bases for the woofers,

Which fit an opening
in the mounting plate.

Brass is the metal
of choice for these parts,

Due to its acoustical
properties.

For aesthetics, the rings
are painted black,

And the mounting plates
are electro-plated

With galvanized chrome.

In this part of the plant,

They build tweeters
for the main system towers.

The first step is to lay strips

Of resin-impregnated
carbon fiber

In semi-circular molds.

After removing
the protective film

That covers the carbon fiber,

They lay foil strips
at each end.

These will direct heat
from the oven

To the carbon fiber strips

And prevent the resin
from flowing out.

They assemble the molds
and clamp them shut.

They place the molds
in an oven for 45 minutes

At a programmed series
of temperatures.

This heats the resin
in the carbon fiber,

Stiffening and forming
the strips to the mold shape.

Using a punch press,

Workers slice
each carbon fiber strip

Into several thinner strips.

They construct each tweeter

By gluing 24
of those thin strips

To the tweeter's voice coil,

A ring made of
wound copper wire.

They brush silicone
in between the strips,

Coat the entire surface
with more silicone,

Then place an aluminum
cover plate on top.

They construct each mid-range
driver the same way,

But with carbon fiber strips

That are thicker and stiffer

And therefore radiate
lower frequencies better

Than the thinner,
more flexible tweeter strips.

Placing the strips with tweezers

And aligning them properly
with a toothpick

Requires a good eye,
excellent dexterity,

And a lot of experience.

Like the tweeter,
the mid-range driver

Goes into an oven
for 45 minutes

Through a specific cycle
of temperatures.

Once the driver comes out
of the oven and cools,

They glue strips
of sound-dampening foam

To the inside,

Sealing the gaps between
the carbon fiber strips.

This prevents sound
from radiating inward

Rather than out the speaker.

They solder the cables

That bring the incoming
electrical signal

That carries
the sound frequencies.

That signal moves
the voice coil up

While the driver's magnet
moves it back down.

The repeated up and down motion

Flexes the carbon fiber strips,

Radiating the sound frequencies.

After installing a center rod
made of carbon,

Workers stuff the hollow space
inside the driver

With sound-dampening wool.

They pour lubricating oil

Into a narrow gap
in the driver's magnet,

Then insert the voice coil
into the gap.

The oil contains iron,

So it conducts the electrical
signal to the coil.

They screw an aluminum
mounting plate

To the magnet's posts...

...then apply a disk of a stiff
sound-dampening material.

They install the tweeter's
magnet on the mounting plate,

Feeding the tweeter's
electrical cables,

Not yet soldered to the tweeter,
through the center rod.

Next they'll make the woofers.

Narrator:
the sound system's amplifier
delivers the electrical signal

That carries all
the sound frequencies.

Inside each main system speaker,

An electronic component
called the crossover

Separates the frequency ranges

And sends them,
via designated cables,

To the appropriate driver.

They make each
melon-shaped woofer

Out of 12 aluminum segments.

They glue acoustic foam
to each segment,

Then trim the foam
to the shape of the aluminum.

Workers assemble the woofer
upside-down

In an assembly fixture.

They glue the segments
vertically

Between this woofer's
voice coil,

Which has two cables
attached to it

And a mounting plate.

The structural rod

Through which they'll feed
the other driver's cables

Is in the center.

Once all the segments
are aligned and fixed in place,

They coat the edges with glue.

Then they adhere rubber gaskets
in between the segments

To block the gaps
and prevent air from exiting.

They seat copper strips
in the segment's grooves,

Hooking the ends into holes
at the top and bottom.

Brass, aluminum, copper --
every type of material used

In these speakers has specific
acoustical properties.

The combination produces
a natural sound balance.

They fill the hollow
interior space

Around the center rod
with sound-dampening material.

First, synthetic insulating wool

With long, coarse fibers.

Then, on top of that,

A barrier
of cotton-insulating wool

To prevent those coarse fibers

From touching the voice coil.

Next, they install
the painted brass ring

They milled earlier,

Which now has the woofer's
magnet fixed to it.

They place a spacer,
thread a screw,

Pull the voice coil's two
cables through the center,

Then solder those cables,

Together with the cables
from the other drivers,

To a main cable that will plug
into the crossover.

They flip the woofer
right side up

And pour a liquid
sound-dampening compound

Into the center rod.

The cables inside
are too delicate

To be shoving in
insulating wool.

Workers now begin
assembling the speaker,

First soldering the two
remaining crossover cables,

Mid-range and high frequency,

To the respective driver cables.

The tweeter connection cables

Are attached
to the tweeter magnet,

Installed earlier on top
of the mid-range driver.

They now mount this unit
on top of the woofer.

They install the connectors
in the crossover.

Its electrical components
separate the frequency ranges

And send each one
to a designated connector,

Which sends it to the cable

Leading to
the appropriate driver.

After sliding the crossover
onto the speaker's base,

Made of milled brass,

They close up the top
with the mounting plates,

Between which they've
since sandwiched

A thick piece of wood.

Screw-in stainless steel
support posts

Hold everything together

And direct all the weight
down to the floor,

Rather than into
the speaker structure.

They install
an aluminum crossbar

For structural support,

Then a second set of posts.

They fit the ring
at the base of the woofer

Into the mounting plate hole,
securing it with screws.

They insert the tweeter's voice
coil into the tweeter magnet

That's mounted on top
of the mid-range driver

That's mounted
on top of the woofer.

They solder the tweeter cables

To the two connectors
on the tweeter cover plate.

This completes
the lower trio of drivers.

Now they install
an identical upper trio,

But upside-down

So that the two tweeters
face each other

In the middle of the tower.

They mount the crossover
for the upper trio

And plug in the connector
that joins the three cables.

That brings
the correct frequencies

To the three drivers.

They run test tones
through every completed speaker.

A microphone positioned
just over three feet away

Picks up
the emitted frequencies,

Which a computer
analyzes for accuracy.

Once the speaker
passes inspection,

They install a decorative grill
over each woofer voice coil.

The subwoofer tower radiates
the lowest frequencies,

With six huge drivers
and a built-in amplifier.