Angle Grinders Berry Baskets Omnidirectional Speakers
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. 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. 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. 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.