May 2022 – Shop Finds

Planisphere

Posted on May 31, 2022July 28, 2022 by Brian Garthwaite

Astronomy at Bucknell is not just for the undergraduate students, but for the wider community, too. With a whole slew of telescopes to explore the skies, the department sometimes runs family nights and other outreach programs. Local families, summer camps, and others can – weather permitting – have the opportunity to explore constellations, deep sky objects, planets, and sometimes even the crater-riddled surface of the moon.

For those at home, an ordinary pair of binoculars works quite well for that last one. Pick a night when the moon is between new and full, and look to the transition zone between the light and dark sides. The light rays raking across the surface dramatically emphasize the texture. The full moon’s straight-on illumination is less compelling, and, well, there’s not much to see on the new moon.

In order to help explain the skies to the public, the Observatory has a planisphere, built by one of the University’s Presidential Fellowship students with the help of the shop techs. A flattened portion of the celestial sphere rotates, enabling a view of the major constellations at any day and time throughout the year. Polaris, at the center, stays steady while the rest of the sky spins about.

For added excitement, a series of colorful LED lights ring the perimeter, making the stars and imaginary constellation lines glow in the etched acrylic.

Planisphere in dark room — *…that really pops in the dark.*

It’s pretty cool.

Lead Bricks

Posted on May 27, 2022July 28, 2022 by Brian Garthwaite

Yes, they’re heavy. Quick estimate, based on their dimensions (20cm x 10cm x 5cm) and density (11.29 g/cm²), each one weighs approximately 11.3 kg (24.8 lbs). That wee stack of 15 bricks runs to nearly 170 kg (373 lbs). Pushing them down the hallway on a large cart gets exhausting, quickly.

Let’s all act surprised that they were left behind in a research lab post-retirement.

These are a prime example of something that we keep around, just in case. Plus, they’re expensive. A very similarly-sized bar of lead from McMaster-Carr – 2 in. x 4 in. x 8 in. – will run you $202.42 at this moment. Fair to say that doesn’t include shipping. It might be more cost-effective to drive to New Jersey for pickup.

To our next nuclear physicist, whomever you might be: we’re holding on to them for you. Come get them anytime.

Variac

Posted on May 24, 2022July 28, 2022 by Brian Garthwaite

When a faculty member retires, they tend to leave a variety of things behind in their labs. With the busiest days of physics research behind them, and only so much spare garage and attic space, old pieces of scientific apparatus don’t make the cut. That doesn’t mean they’re not useful to someone else. Sometimes old equipment, built for a long service lifetime, still works pretty well. Those few things built without integrated circuit boards and lacking in bells and whistles? They’re tanks. We collect those, make sure they’re in good working order, and keep them handy for the next person who needs them.

Take, for example, the good, old-fashioned variable autotransformer, often called a Variac in the same way you might refer to any office copier as a Xerox machine. There are easily half a dozen floating around here. Probably more if you take time to look in the dusty corners. The short version is this: you send in ordinary AC line voltage, turn the big, chunky dial, and it sends out a lower AC voltage based on that setting. It has two moving parts: a sliding brush that moves along the wiring coils, and a switch.

Always love a reliable mechanical switch. Click!

An autotransformer has only one winding inside it, and outputs one or more voltages different from its input depending on where they tap into the coils. (A standard transformer has two windings. There are pros and cons to each.) A variable autotransformer has a sliding/rotating connection on the secondary side, enabling smooth voltage change from more or less zero to full. The number of coils the current passes through on its way to the brush’s connection determines the output voltage.

It takes advantage of the constantly-changing nature of alternating current. The flow of current creates a magnetic field; a changing current creates a changing magnetic field. A changing magnetic field creates a current in a circuit. Plugging a variac into the wall receptacle works. Connecting up a DC battery won’t.

They’re handy for testing electrical equipment, including motors whose speed is voltage-dependent. We use them in undergraduate labs in connection with incandescent lamps to study blackbody radiation; they’re a big dimmer switch that’s easy to control and understand. The core of a Mel-Temp apparatus, that workhorse staple of a chemistry lab setup, is just a Variac connected to a big resistor. The varying voltage adjusts the current, which controls the amount of heat it gives off to melt your sample.

Some of the old styles are Art Deco-ish beauties, too, with amazing names. Adjust-A-Volt! Powerstat! Every space-age laboratory deserves a few of these.

Micro Bits

Posted on May 19, 2022July 28, 2022 by Brian Garthwaite

Acrylic with very tiny holes — *Very tiny holes*

In the Physics & Astronomy shop, we make, modify, and repair things. When the thing you need just isn’t available off the shelf, it’s our job to make it happen. If at all possible.

(It’s not always possible, but we give it our best. Sometimes we surprise ourselves.)

The end result is a lot of unique, one-off objects built to do very, very specific things. They may be lab or research equipment to our colleagues, but they’re learning experiences for us. You never really know what sort of experience and expertise is going to come in handy down the road. And, yes, we make mistakes along the way.

Our desktop CNC mill makes this process just a little bit easier. We get the sort of repeatability and precision alignment in a fraction of the time it takes on a manual machine, and it can turn out tiny work that our eyes struggle to see without magnification. Recent software updates have given it proper drilling capabilities, letting us use an assortment of very small drill bits to expand the sorts of work we can accomplish. Does a project call for precisely-drilled holes on a very small scale? We can do that.

See above for 0.5mm drilling. Now an option!

Until the bit snaps. Occupational hazard.

Solar Telescope

Posted on May 17, 2022July 28, 2022 by Brian Garthwaite

There are a wealth of options when choosing a telescope. Refractor (lens), reflector (mirror), or catadioptric (both)? How large an aperture (because letting in more light lets you see fainter, more distant objects)? Manual or computerized control? Optical viewing, astrophotography, or both? Alt-azimuth or equatorial mount? And so on. Dedicated astronomers can get deep in the weeds on the finer details.

What they all have in common is a BIG WARNING often in BRIGHT RED ALL CAPS that you should never, ever, point your telescope at the Sun. It’s solid advice.

Looking directly at the sun with your naked eye is likely to cause permanent eye damage. Doing so with the extra light-gathering power of a “light bucket” only accelerates the problem. Even if you don’t peer through it, the heat that builds up within the telescope’s delicate optics is enough to irreparably damage them and ruin your very expensive equipment. What’s an aspiring solar astronomer to do?

Find a solar telescope, of course. A few special features make this telescope safe for solar viewing (and somewhat less useful for anything else). It has a very small aperture, because it really isn’t necessary to collect more light from the brightest thing in the sky. It has a small section of opaque glass on top of the telescope which shows a pinpoint of light when the sun is approximately in view. And, best of all, it has an narrowband filter around H-alpha.

H-alpha is a specific wavelength of light emitted by excited hydrogen atoms, about 656nm, and the brightest hydrogen emission in the visible wavelengths of light. It’s quite red. It’s also, through a suitably narrow filter, something you can safely observe with your eyes. Pare away the other visible light, all of the UV and IR, and you’re left with the sun. Red, intense, and through the proper set of optics, magnified so that you can see amazing things.

Prominences erupting from the surface. Dark filaments that indicate region of magnetic shear. Sunspots and flares. The speckled, roiling surface of a star that’s like an orb of churning lava. It’s very cool. Astronomy you can study without staying up all night.

Still a bust on cloudy days.

Drinking Bird

Posted on May 11, 2022July 28, 2022 by Brian Garthwaite

Greetings from one of the unofficial mascots of Physics, the drinking bird! Forever wearing its top hat, this classic toy is found all around the department. Though we keep a drawer full of them in storage, there are a handful about the shop shelves, professors’ offices, and occasionally elsewhere. The drinking bird is an example of a heat engine, which converts heat into mechanical energy.

Drinking birds are especially fun because they operate at room temperature. Two glass bulbs are connected by a tube and filled with methylene chloride, which has a low boiling point and condenses and vaporizes readily within the vessel. When the upright bird’s felt-covered head is wet, evaporative cooling causes a vapor pressure differential between the two ends. As liquid from the bottom rises, the bird becomes top-heavy and leans down for a drink, re-wetting the felt and priming the process to repeat. It’s an entertaining demonstration of the effects of various laws of physics.

There’s the ideal gas law, of course. Temperature change causes pressure change, which causes a shift in the balance of liquid and vapor. That shift in mass results in a center of mass that oscillates from one side to the other of the fulcrum, creating torque and movement. For as long as the bird can re-wet itself and maintain the temperature differential, the heat engine will continue to operate.

Alternately, you can apply a heat source to the lower bulb to get the same effect, which is the basis for most heat engines. There are many options to produce heat, and a wealth of engine designs to turn that thermal energy into useful work. But few are as simple, visually apparent, and entertaining as a bobbing glass toy.

Cast Acrylic

Posted on May 9, 2022May 9, 2022 by Brian Garthwaite

We work with a wide variety of materials in the shop, each of which has its strengths and limitations. One frequent visitor to the milling machine is cast acrylic, a clear, lightweight, machinable thermoplastic. It’s known under a variety of trade names, such as Plexiglas and Lucite, as well as polymethyl methacrylate (or PMMA).

Acrylic is often used as a replacement for glass, for its high light transmission (~92%), lower density, and higher impact strength. It is still brittle, and nowhere near as strong as polycarbonate, but won’t suffer from UV degradation and can be used outdoors. Acrylic mostly machines well, although requires extra care with thin sheets and work near edges, where even a small excess of force can cause fractures. We have been using it to replace fragile glass sheets throughout the department’s labs.

Careful sanding and polishing can produce optically clear pieces, so that researchers can observe the inner workings of an experimental setup. Acrylic is also available in a selection of fluorescent colors – red! blue! green! amber! – though, oddly enough, we have yet to receive a request for a fluorescent green vacuum chamber.

One of these days, someone will roll into the shop with a project that demands Bucknell-themed fluorescent blue-and-orange (amber), and we will be ready.

One last fun note: most materials have a distinctive smell when cut on power tools. When cutting or milling acrylic – especially on the bandsaw – the aroma is vaguely fruity, like a distant cousin of whatever chemicals make Froot Loops cereal taste like “froot.” When coming across an unmarked sample of clear plastic, sometimes its distinctive smell is enough to help identify.

Hot Glue

Posted on May 6, 2022July 28, 2022 by Brian Garthwaite

Our inaugural object is a well-loved, frequently-used tool here in the shop: the hot glue gun. Sometimes the most useful tools are ordinary and un-fancy. See also: screwdrivers, needle-nose pliers, masking tape.

Hot-melt glue is amazing stuff. Its ability to melt and ooze into the surface texture of a wide variety of materials means it can effectively bond adhesive-resistant stuff, such as polyethylene. Plastics, metals, wood, paper: no problem. You do need to be aware of how quickly it cools down; aluminum’s thermal conductivity can re-solidify the glue faster than you can squeeze your pieces together if you aren’t quick.

It’s also free of solvents, requires no mixing or curing or complicated steps, and is as easy to use as you remember from junior high. What more could you ask for?

The P&A Shop

Posted on May 5, 2022July 28, 2022 by Brian Garthwaite

A typically messy electronics bench — *The electronics bench*

Welcome to Olin Science 181, the Physics & Astronomy department’s machine shop. As the department’s support team, we regularly discover, design, and build all sorts of curiosities. This blog is just a small sample of the fascinating things we come across every day.

They’re interesting. Sometimes strange. Sometimes oddly charming.

Always worth sharing.

Month: May 2022