Most impressive is that the yellow paint has lasted this long.
It seems the university has drifted away from this, but if you look around at old equipment, a great deal of it is marked with the date it was acquired and – if it’s old enough – the cost. They’re fascinating glimpses into the past.
Here, an optics bench made by the Central Scientific Co. of Chicago, Illinois. Or, as they’d prefer, Cenco of Chicago, U.S.A. This particular 132cm chunk of cast iron and steel joined the department in late September of 1943, for the low, low price of $40. According to the U.S. Bureau of Labor Statistics’ CPI Inflation Calculator, that’s an excessively specific $681.17 in today’s dollars. (Significant digits!)
Surely there’s a reason for the cities listed in that order.
Up until now, it’s been in more or less continuous lab use, only recently replaced by brand-new extruded aluminum optics benches. Almost 80 years, and they’re not entirely kaput just yet.
After all, if an apparatus continues to be useful, we’ll keep it around. This one is getting repurposed for future labs, so we’ll see how many more decades it has in it…
Dice! Bins of colorful dice, each with 178 of one bold color, plus two going their own way. Each bin arrayed in a 10 x 18 or 12 x 15 grid, per the shop tech’s preference at that moment. Beats counting them one by one.
Secure the lid and shake with all your might: you’re simulating radioactive decay! Loudly.
Pick a number from one to six. Say, three. Each die that turns up with three pips after a shake decays, and you remove it from the bin. With 180 dice in there, the chances of getting all threes – or zero threes – is vanishingly small. One-in-six raised to the 180th power, right? As a percentage that’s, what, nearly 140 zeros after the decimal point? Run the numbers, and you can look forward to around one-sixth of the dice in there decaying with each shake. Sometimes more, sometimes less.
You’ll also keep a close eye on those differently-colored dice. One for you, one for your partner. They’re the atoms you’re watching carefully, and unlike the sorta-predictable rolls of a large mass of dice, they’ll decay when they’re good and ready. Could be first, could be never. It’s an illustration of how probability works in systems of different sizes. Of how the random nature of radioactive decay produces a predictability with enough atoms and enough time.
In some idealized version of this experiment, you’d have 30 dice decay on the first shake. Then 25. Then 21. 17. 15. 12. 10. 8. 7. 6. 5. 4. 3. 3. 2. 2. 2. 1. 1. 1. After that… maybe one per shake? (The student experiment stops well before you’re down to a meager handful of dice.) The half-life arrives around four shakes. Every four shakes. Neat!
And should the effect with 180 dice not be enough? Compare your data to the rest of the lab, seeing how each rate of decay is nearly but not exactly the same. Then aggregate the data from all dozen lab benches. 2,160 dice decaying.
When we describe a typical day in the shop, we always hedge and point out that there is no such thing. Walking in to work every morning, you wonder what surprises the shop has in store. At any time, the most unusual requests will walk through the door. Yes, we set priorities. Some needs are more pressing than others. Certain departments (the ones whose budgets support us) get preferential treatment. Some jobs can simply be done in just a few minutes.
We’ll stop all but the most important, time-sensitive work to fix a problem that only takes a few minutes.
Then there are the times when a project is going someplace unexpected. Testing out new ideas. Research outside the usual comfort zone. To be clear: research is always stretching into new, unexplored territory; that’s what makes it so fascinating! But sometimes that territory includes stepping outside the lab.
Physics: not typically set up for regular fieldwork.
Recently it’s become important to brush up on knot-tying. Good, sturdy, easy-to-remember knots for an unusual situation. Testing, tying, repeating. (Making a few mistakes; correcting.) Settling in on the bowline, the alpine butterfly loop and bend, and the trucker’s hitch. Good names. Better knots.
The bowline – rabbit, hole, tree, etc. – is simple to tie, won’t come undone under load, and makes a sturdy loop to fix one end of a rope. A dedicated individual can even tie it with one hand. Let’s all hope it doesn’t come to that.
The alpine butterflies are a pair of near-identical knots for different purposes. The loop creates a sturdy loop in the middle of a length of rope, and can be used to shorten a rope, too. It won’t slip or bind, and no matter how hard you pull it, it’s still a breeze to untie with fingertips. A bend, in knot-tying parlance, connects two lengths of rope, and the alpine butterfly bend is simply a variant on the loop where two ropes of about the same thickness tie together. Repair a damaged rope. Create a longer one. Tie one length into a giant circle. You’ve got options.
Plus, they look neat during the tying process, which wraps the rope about one hand in a butterfly shape before snugging tight. Makes it super-easy to remember, and if you’re learning a series of scouting knots, you know you’re going to end up someplace you can’t check your phone for a last-minute refresher.
Practice, practice, practice.
And then… the trucker’s hitch. It can start with an alpine butterfly loop (so why not?), then loops back about itself to provide a pulley-like mechanical advantage to tighten it down. Just keep pulling the loose rope until you reach the right tension, freeing you from the need to perfectly guess your length. A pair of half-hitches finish it up, distinct from the load pressure, making it a snap to untie when the time comes.
So. Bowline to start at one end. Alpine butterfly for a solid loop, leading into a trucker’s hitch that can tighten down as hard as we can make it. Keep our loads solid and stable in the wind and weather, and they’ll still untie in moments when we’re done.
Can-knot wait to see how this plays out in the field.
What’s your favorite holiday? Whichever you choose, it’s kind of like that around here, because it’s almost toy kit time! Classical and Modern Physics I – better known ’round here as PHYS 211, or just plain old 211 – gives out a bag full of toys to each and every student. More than three hundred of these are getting ready for distribution.
We do the same for PHYS 212 in the spring, with all sorts of goodies for electricity and magnetism, but in the fall, it’s all about mechanics. Stuff that moves. Toys, exactly like you’d expect them to be. Yo-yos, Slinkys, bouncy balls, blowdart guns, drinking birds, and more.
Always balloons. Every toy kit, every semester, we include balloons. For science. More specifically to help illustrate the principles of physics for homework and problem-solving sessions. What better way to learn than with hands-on experimentation?
Here we have that childhood classic, the Duncan Imperial. Some of the kits will get the Butterfly instead – when you go purchasing hundreds at a time, you take what’s available and fits in the budget – but either way, it’s the return to a certain moment of childhood. At least for the shop techs. If there’s anyone in this world who’s guaranteed to get excited about nifty gizmos, it’s us.
(If there’s anyone in this world who can have serious conversations about the varying quality and potential factors affecting a bouncy ball’s bounce, it’s us. But that’s a topic for another time.)
And, since you were bound to ask: no, neither of us can remember how to do any of our childhood yo-yo tricks. Doesn’t stop us from trying.
There are bits of information worth remembering, and others best outsourced to a handy reference. Preferably one that isn’t Wikipedia. Having a head crammed full of a broad swath of information is immensely handy in a shop with such wide-ranging activities. When an unexpected request comes through the door – and so many of them are unexpected – it’s refreshing to be able to approach the problem with at least some sense of which direction to take.
Even if you can’t pull up the specifics, knowing the outline of the process gets you started. A tiny dose of confidence helps, too. That and a willingness to give just about anything a shot. And, yeah, stuff gets broken sometimes.
Mental outlines are good. Instant recall of key facts is useful. Sometimes, though, you need a big table of numbers, because by the time you’ve committed that mountain of stuff to memory, you’ll have forgotten why you were even trying in the first place.
A big table, but not so big it won’t fit in a pocket. (Side note: you will always be happy to have a spare pocket around here.) Side A lists drill sizes with their diameters in millimeters (to 2 decimal places) and in inches (to 4 decimal places). Fractional from 1/64″ to 1″. Wire from 80 to 1. Letter from A to Z. Metric from 0.10mm to 25.5mm. 206 in total. (Assuming you consider 1/4″ and E to be separate drill sizes. They’re identical, save for the markings on the shaft.)
It’s especially helpful when trying to find just the right size for a project. That 1/4″ plastic tubing that needs to fit snugly-but-not-too-snugly? The 1/4″ drill probably won’t work. Size G, with a spare 0.28mm, might.
…only the most commonly used ones.
The B-side to this is a pair of tables that match up thread sizes – national coarse and fine; taper and straight pipe; metric – with the appropriate drill. The metric table even provides SAE alternatives should you find your metric drill selection somewhat less comprehensive than the full array of letters and wire numbers. Perhaps DoALL was more optimistic about an eventual shift to metric back in July of 1986.
Regardless, the table’s ease of converting between fractional inch, decimal inch, and millimeters is immensely useful in a shop where all three options might come into play. The availability of raw materials sometimes creates situations where you’ll work with both SAE and metric on the same job. It’s weird.
Honestly, here in the shop, we’d prefer to do everything in metric. Makes the mental math way easier.
Drawer label says “Radio Knobs,” and that’s actually what’s inside.
There’s a tendency in the shop to scrounge and save almost everything. You never know when something might come in handy, and experience has shown, over and over, that there’s value in all but the junkiest junk. And even that, if sufficiently large/heavy/whatever, can be an effective doorstop, or spray paint shield, or otherwise helpful bit of plain old physical mass. When a piece of equipment breaks and is just irreparable, you dig out the good bits and set ’em aside.
It’s important to keep track of which boxes contain the useful bits and which the junk. Sometimes the difference isn’t immediately obvious.
There’s a drawer in one of our storage rooms labeled “Radio Knobs.” Indeed, that’s what’s inside. Collected by our predecessors from an array of broken equipment, calmly waiting their turn to be useful once more.
Not a lot of carpet in a machine shop. With the exception of a few small squares adhered to the bottom of certain table legs – they slide better! – there’s none to be seen outside our offices. Carpet would only tangle up the metal swarf, and that’s all-around no good.
(Incidentally, mouse pads are excellent for sliding furniture about. One side slips, the other side grips. Use them wisely.)
So why carpet tape? It’s a powerful, but not too powerful, double-sided adhesive with a woven cloth embedded within. When working with various machines around the shop, we have different tools at our disposal to hold our workpiece in place. A whole mess o’ clamps and vises to lock down most objects. Chucks to hold drill bit and mill bits and material turning in the lathe. There even exist mini versions to hold pieces in the CNC mill.
But we usually go for tape. Sometimes masking tape. Sometimes packing tape. 99% of the time, carpet tape.
It’s strong stuff, but not so strong that a heavy-duty putty knife can’t help you pry the work free. It’s only on the bottom of the workpiece, so you don’t have to design your toolpaths around it. It cuts easily with scissors, enabling you to place it strategically around your stock, minimizing the amount that comes into contact with a spinning end mill. Then, if it does, a shop rag and a little isopropyl alcohol cleans things up in a moment.
Isopropyl alcohol: handy solvent, very low toxicity (assuming you don’t drink it), evaporates rapidly. Inexpensive, readily available, and effective in very small quantities. Wonderful stuff.
On top of that, the low-adhesion, slippery paper that wraps the tape is easily measured with a micrometer. We keep a few scraps of that handy, enabling us to readily set the zero height of the mill without the tool ever having to contact the stock. (Current tape roll thickness: 0.1 mm.) Measure the new roll each time, make some notes, and you’re back to work.
It’s the gift that keeps on giving. And occasionally sticking to everything in sight. (It’s powerful stuff.)
Need to connect one thing to another? You have options. Somanyseeminglyendlessoptions. And, yes, digging through all of that will reveal treasures upon treasures, from more head drive styles than you can imagine ever needing – at least twenty-two – to nuclear-grade duct tape to plain old Elmer’s glue sticks. (We have yet to find a use for nuclear-grade duct tape around here, but glue sticks come in handy sometimes.)
Mechanical fasteners, specifically screws, see a great deal of use around here. Among other benefits, they’re easy to remove. When you spend your days making and modifying things, leaving open the possibility of taking an apparatus apart and swapping in a newer, better piece is reassuring. Sure, it means tapping a lot of holes instead of simply running a bead of adhesive. Trade-offs.
The variety of socket head screws alone can be mind-boggling. You could make an entire career out of just maintaining the ANSI standards on those things. Presumably someone does. Several someones.
For most jobs, alloy steel will do. Strong, inexpensive, and available in every length and thread imaginable. If it’s going someplace where it might get wet, zinc-coated provides corrosion resistance. Or upgrade to 18-8 stainless steel, which isn’t as strong but is more corrosion resistant. If it’s passivated, even more so. Black oxide if you want a matte-black finish; chrome-plated if shiny’s the thing. Silver-plated “have mild lubricity so they thread smoothly.”
New vocabulary word: lubricity.
316 stainless is more corrosion-resistant. A286 stainless are as strong as alloy steel, as corrosion-resistant as 18-8, and so expensive that they’re sold as single screws only. Save those for the next time you’re building an aircraft.
Then there are the other metals, each with special applications. That often includes resistance to corrosion from salt water or other chemicals, and if that’s where you find your project, get ready to do your homework. “Corrosion-resistant” is a big umbrella.
Sometimes you’ll get an even more unusual request: build a gizmo without any metal. Metals, especially ferrous ones, tend to cause trouble when working with magnetic fields, and physicists love them some magnets. Steel’s out. Brass, bronze, and aluminum are nonmagnetic, but are conductive enough to generate potentially disruptive eddy currents in a changing magnetic field. Could present a problem. That leaves plastic.
Plastic. The standard is nylon, which is strong, durable, and light. It may also expand when wet, so watch out for that. Polypropylene is more resistant to various chemicals and doesn’t swell in water, and you can expect to pay for those added benefits. Then there’s PEEK. Polyether ether ketone. Strong. Resistant to a whole array of chemicals. Happy up to 500° F. At several dollars per screw, you’ll know when you need one.
