Vectors

Posted on by Brian Garthwaite
Force table apparatus.
Three-way tug of war.

The humble force table. A flat surface, graduated with single-degree marks. Three pulleys which may be clamped at any position. Loops of string connected to a central ring surrounding a post, each of which is pulled by a mass hanger of 50 grams.

Move those pulleys about, slip on some extra masses, and try to keep the central ring from touching the post!

If you’re going by gut intuition (and not just doing the silly trivial 120° spacing with equal masses), be prepared to make mistakes and incremental adjustments. There’s no way you’re nailing this on the first attempt. Slowly making corrections, adding and removing masses, trying to get that central ring to hover just right, it’s fun. Yes, folks, vectors and statics can be genuinely enjoyable.

The students get to explore that, of course, but it’s also an opportunity to learn a bit of Excel. Build your spreadsheet properly, and you can predict the precise angles and masses needed for equilibrium. Set it up and, presto, it works!

As a test, they run it in the opposite direction, too. Set some angles, add some masses, get it to balance. Type those numbers into the spreadsheet, and… it’s not quite right. The math says it’s off, but the ring says it’s fine. Weird! It’s a handy introduction to measurement uncertainty, a tactile illustration of a critical concept.

It’s very cool.

Bird droppings

Posted on by Brian Garthwaite
Bird dropping on telescope.
Yes, this telescope can rotate all the way around.

Telescopes don’t work when they’re not at the same temperature as the surrounding air. They don’t work if there is glass between them and the sky. (Okay, they work, just not very well.) So: you use them outside, and any space used to protect them from the elements is best if it’s as much like outside as possible.

Observatory domes, retractable roofs, etc.: all very fancy ways to keep the rain off.

Wildlife has a habit of getting into these spaces, especially the small critters. Spiderwebs are a frequent feature. Birds appreciate the shelter from the elements, and will happily build nests if given sufficient access. It’s amazing what they’ll squeeze through, if for no other reason than to leave a stark white splotch on an all-black telescope. At least it seems that way.

This doesn’t include the exterior-only wildlife population that brightens up the occasional observation session. Nocturnal critters get used to the quiet around daytime spaces, so it’s best to keep alert for opossums and skunks and other adorable visitors when out late at night. That black-and-white blur is probably just a feral cat, but you know what? Best not find out for sure.

Force table

Posted on by Brian Garthwaite
Force table with acquisition info.
More yellow paint!

Some equipment just keeps on working, year after year. This force table – an apparatus used to illustrate static equilibrium and vectors in a way that’s loads more fun than Excel, but the students still have to learn Excel – was purchased in February of 1957 for the not-insignificant sum of $87.50.

Today’s dollars: $935.89.

Circuit Boards

Posted on by Brian Garthwaite
Broken circuit board.
Guts.

Ah, the printed circuit board. Svelte. Densely packed with teeny marvels of modern electronics. Those parts big enough to be labeled usually require magnification to read the text. The really little ones? It’s not really possible to replace those anyway, so just trust that they’re working as intended.

Until the whole gizmo isn’t working as intended, of course.

When that happens, it’s time to make an assessment of what can be fixed. Sometimes it’s a loose wire. Sometimes it’s a frayed cord, or a bad switch that’s not part of the circuit board itself. Not that these are likely, but it’s best to be thorough.

Assuming you can get the housing open to inspect it. These suckers aren’t built with repairs in mind, given that purchasing a whole new item is less expensive than the cost of labor plus the replacement value of what’s 98% of the whole item. So many tiny screws. So many snap-fit plastic parts. At some point you realize how much thought and effort went into designing this object for quick assembly, and how little went into ease of disassembly.

Pictured above, a faulty motion sensor, has no obvious loose connections or broken parts. It simply fails to collect consistent data, with erratic drop-outs punctuating the signal. Oh, well. Maybe it’s good for parts?

“The Pit”

Posted on by Brian Garthwaite
Bilco door.
Feed the pit.

When you have a regular need to open lots of doors – accessing equipment, supplying labs and classrooms, helping coworkers find their misplaced keys – the powers that be may be kind enough to cut you a master key. Saves time, effort, and several pounds of metal on a keyring. They are, of course, master keys with a limited range. Certain doors are off-limits.

The access door to the elevator-base maintenance? That’s a place we don’t need to be. It’s only important that we don’t stack anything of substance on top. (The roll of plastic seen here could be blown away by a light breeze.) Not that it wouldn’t be neat to have a look inside – after all, who wouldn’t like to check out some new kind of specialized machinery? – but if the elevator’s working, maybe let it be.

That said, it’s hard not to be fascinated by the accompanying light switch:

Pit light switch.
“Pit Light”

Sure. Of course. How else would you label it? Dark, forbidden basements should always get the proper horror movie styling.

And then there’s the nubbin of a switch. Makes one wonder. Can’t possibly be from overuse. (Can it?) Implies that someone did that on purpose.

Maybe the answer’s down in the pit.

Signs

Posted on by Brian Garthwaite
Caution sign.
Caution. It’s like a welcome mat!

Signs! They’re all around, some not-so-subtle hints to remind you that you’re in a working machine shop full of dangerous things. There’s an informal ranking of which tools qualify as the most dangerous, but improper use can make anything a hazard. So it’s safety goggles required, watch your fingers, and don’t touch anything you haven’t been trained to operate safely.

Can we assume you understand that open-toed shoes are a no-go?

Hazard signs have a hierarchy, beginning with CAUTION, often in yellow. Caution tells you that you’re in a potentially hazardous place, and failure to take appropriate precautions could result in injury. Safety goggles around the machines, please. Don’t press any switches unless you know what they do.

Warning sign
Warning. Seriously, don’t touch anything if you don’t know what it is.

Next step up: WARNING. The situation here is moderately hazardous. Failure to take appropriate precautions could result in death or serious injury. Maybe not likely, but please don’t lose a finger to the bandsaw. Keep those knuckles well away from the business end of the belt grinder.

Danger sign.
Danger. These machines will bite.

And at the top, DANGER. Oh, danger. You get the quality of imagery that belongs on packs of cigarettes. Danger tells you that certain situations will result in death or serious injury. Not might, but will. Do not mess around with the table saw. Do not allow loose clothing or hair anywhere near the lathe. We like gallows humor for some very good reasons.

Nothing quite like the worst-case outcome for Charlie Chaplin in Modern Times laid out for you in stark silhouette.

Reference Books

Posted on by Brian Garthwaite
New and Full Moons cover
Did not budget for graphic design.

It’s no surprise that there are books everywhere. This is a university, after all. Books are one of the biggest threads connecting every department and avenue of study.

Sometimes it’s fun to flip open some of the old tomes gathering dust on mostly-forgotten shelves. This was, presumably, a useful reference when acquired in 1973 or so. Flipping open the front cover, it’s not hard to imagine that someone got at least $5 worth of use out of this.

Inside flap.
Five bucks.

That said, this is not the most compelling cover-to-cover read, unless you’re really into data tables for the sake of data tables. Front to back, it’s tables of lunar positions and times over a span of 2,652 years. From what seems like an arbitrary start – 1,001 is a pretty fine number – to around the death of Johannes Kepler (November 1630) makes for a lot of potential eclipses and other lunar phenomena that would get the attention of ancient writers.

Folks around here are already talking seriously about the solar eclipse in April of 2024. Syzygies are a big deal.

Syzygy. Y-Y-Y. Great word.

Toy kits

Posted on by Brian Garthwaite
Toy kit components.
Teaching aids.

‘Tis the season for PHYS 211 toy kits!

A bag full of goodies for each and every student studying classical and modern physics this upcoming semester. Yo-yo, fidget spinner, bouncy balls (large and small), rubber ball on string, silicone fun poppers (large and small), metal coil spring (not a Slinky, but really it’s a Slinky), and a pair of balloons. Drinking birds and blowguns (not pictured) to be distributed later in the semester.

For those wondering: the big bouncy ball is way better than the little one. Same goes for the fun poppers. The little ones hop a bit, while the big ones bounce all over the shop. You know, for science.

Broken taps

Posted on by Brian Garthwaite
Broken tap.
Not the first time. Unlikely the last.

Tools undergo a great deal of stress in doing their job. They wear down, dulling their edges. There are impacts, intended and not. There’s a lot of force, and heat, and effort in shaping raw materials into something more useful. Tools are generally made from hard materials, intentionally harder than the material they’re working. Harder materials, broadly speaking, are more brittle.

So they’re good, they’re good, they’re good… oops. Broken.

A lot of the shop’s milling and milling-adjacent tools are made of high-speed steel (HSS), a group of steel alloys which perform well at high temperatures without losing their temper. Tungsten carbide (often called carbide) is even harder, and we save those for jobs that need it. Carbide’s brittle enough that it can’t be used in hand tools, instead requiring a sturdier, rigid setup like a milling machine, a drill press, or even better, a CNC machine.

They’re awfully expensive to replace.

Some tools, though, require human hands and a deft touch. Taps are one such example. The action of cutting threads takes firm yet gentle pressure, with frequent pauses and reversals. The tap gets hot; the material gets hot. The corresponding thermal expansion makes the tap more and more difficult to turn, increasing the risk of fracture. Best be patient.

And sometimes, despite all that effort? The high-pitched *tink* that tells you the tap snapped. It’s subtly different from the similar sound that a curled, not-yet-removed burr of metal makes when the tap runs up against it. Sigh.

Reverse the tap, slowly, carefully. See if you can remove the broken piece without damaging the hole. Remember that it’s harder than the material it’s in, and probably as hard as the drill bit you’d like to use to dislodge it. If need be, drill a new hole and try again. This particular tap met its end putting threads into cast iron, a less-than-ideal material for most of our machining jobs.

Mistakes. They happen.