shop – Page 3 – Shop Finds

Pocket reference

Posted on July 13, 2022July 28, 2022 by Brian Garthwaite

Reference card — *Not all of the drill sizes, mind you…*

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.

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.

Carpet tape

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

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.)

Nylon screws

Posted on July 1, 2022July 28, 2022 by Brian Garthwaite

Need to connect one thing to another? You have options. So many seemingly endless options. 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.

We keep the nylon ones handy.

Screw Chek’r

Posted on June 22, 2022July 28, 2022 by Brian Garthwaite

Thread size check plate — *“Chek’r” shows their foresight for SEO way back in 1960.*

One of the ever-unfurling mysteries in the shop is this: what screw thread am I looking at? There are a multitude of reasons to pick one when designing an object, and while we’d all love for simplicity and consistency across a single piece of equipment, that’s not always the case. Hence, a precision-made piece of steel. Holes, smooth and tapped.

Smooth bores identify the screw size – SAE number standard or fractional inch – and are all marked with the corresponding drill size. For size 4 screws, number 33. For 1/4″ screws, a convenient 1/4″. In a moment of serendipitous coincidence, size 10 fits in a number 10 hole. All are marked in the right column with their diameter in decimal inches.

The threaded holes come in three flavors: N.C., N.F., and N.S. Sometimes N.S., at least. National Coarse, National Fine, and National Special.

Coarse threads are standard, and like all SAE threads indicate the number of threads per inch. (Metric threads use the pitch, or the center-to-center distance between threads.) If ever unsure, the answer is that it’s probably coarse thread. Double-check by seeing if it turns neatly into the hole.

Fine threads have certain uses, such as in locations where there will be a lot of vibration. More threads per inch means more contact area for the screw, and the increased friction helps reduce the screw’s ability to wiggle loose. For some reason, they never seem to wiggle in more securely.

Special threads show up in special situations, and are completely inconsistent across the range of sizes. Most are even finer threads, but #4-36 is even coarser, and #6-36 sits in between coarse and fine. Small fractional inch sizes don’t have special designations, and the small number sizes don’t… except for size 1.

Which is an uncommon screw size, to say the least. If we have any in here, they’re hidden away in some dark drawer. We do have a single #1-64 tap, so either they were around for a little project once, or a previous shop tech was very thorough in ordering tools.

Inspecting the Screw Chek’r more closely, you might notice that one of the tapped holes isn’t like the others. Several feel as though they’ve gotten a lot of use over the years – #4-40, #6-32, #10-32 – but poor, lonely #1-56?

No one has ever tried to thread a screw through that hole. There’s still a steel burr in the bottom.

It makes some sort of sense. #1-56 screws are rare as hen’s teeth these days. McMaster-Carr doesn’t carry any, and they have seemingly everything. A quick internet search will turn up hobbyists repairing early-20th-century equipment trying to locate replacement screws in that size. Even a glance at Ruelle Industries’ most recent versions of the Screw Check’r reveal that they don’t even put that thread size on anymore.

Of course, if you can’t find the precise screw you need, that’s what a metal lathe is for…

Hastings Triplet

Posted on June 10, 2022July 28, 2022 by Brian Garthwaite

We field a lot of requests for small objects in the shop these days. It’s not that there aren’t plenty of big/huge/enormous things worthy of serious research and scholarship (see: stars), but physics sometimes gets wild when you go small. And not even quantum mechanics small… that’s where calling physics not intuitive doesn’t even begin to cover it.

We’re talking channels and structures where 100 microns makes a difference. A micron, or micrometer, is one-thousandth of a millimeter; 100 of them is a tenth of a millimeter. In the general ballpark of the width of a human hair. It’s the scale where you learn the finer points of a tool’s tolerances, where you set a machine to do the work and wait until it’s all finished to figure out if it worked.

Mistakes happen.

Very tiny things also defy your eyes’ ability to inspect them, so we rely on microscopes and other optical magnifiers to check on the quality of work. One of the handiest is the magnifier shown above, a Bausch + Lomb Hastings Measuring Magnifier. It uses a Hastings triplet lens system, composed of three separate glass lenses bonded into a single, composite lens. Doing so produces crisp, distinct images without distortion. At the end it has a scale, so that we can press it against an object to inspect and actually measure features less than a millimeter across!

View through loupe — *Very small. Very small.*

One of the best features of this magnifier is its portability. At 7X magnification, it’s less powerful than a microscope, but its case fits in a pocket, so it can go anywhere. Clear plastic sides admit plenty of ambient light, removing the need for additional illumination that a microscope requires. You simply pick it up, inspect your object, and carry on. Confirm that microfluidics channels are the proper width. Ensure that you’ve cleaned all the swarf away from tiny features. Examine tools up close for minor damage to their edges.

Or check out the tiny world all around you, just because you can. Some of the best science starts with noticing something neat, and just digging deeper.

Trig-O-Matic

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

With enough drawers, boxes, bins, and dark corners in our shop and storage rooms, you’re bound to run across the occasional tool that you wish you’d known about sooner. Maybe it’s useful. Maybe it’s fiercely specific. Maybe it’s just a special sort of ingenious. Maybe it’s a pair of squeeze-and-strip wire strippers.

We have several pairs, but only this one is dubbed the Speedex TRIG-O-MATIC. Nothing like a glorious Space Age name to capture that little extra bit of attention.

Feed an insulated wire through the clamps – or several, once you’ve had a bit of practice – up to the adjustable guide. As you start to squeeze the handles, the left-side clamps gently grasp the wires, holding them steady. Then the notched blades close, cutting through the insulation surrounding the wire. The last step in this little dance splits the tool down the center, pulling wire and insulation in opposite directions, effortlessly.

Cleanly stripped wire, courtesy of the two ugliest birds you’ve ever seen. (What two-headed oddity do you see in that picture?)

At this point, you may be wondering when a relatively complicated gizmo like this would be worth having. After all, it has a lot of moving parts, and the more parts something has, the more parts it has that can break. A pair of basic wire strippers, or even just a pair of pliers with wire snips can do the job quickly and cleanly. Right? Well, there are two situations when this little tool is just the bestest thing ever.

1) When a novice needs to strip a few wires and doesn’t need to spend the time (and mistakes) to learn good, practiced technique. We were all there once.

2) When it’s time to put together toy kits for PHYS 212, and all of those lengths of wire* – each with two ends! – need to be stripped and tied. After a while, you get very good at clipping several at once, until it becomes a game to see how many you can manage. Yes, there’s a ceiling.

Toy kits! A subject for a future post: each semester, we put together hundreds of packs for the PHYS 211 and 212 students, full of odds and ends to use for problem sessions. They’re wondrous assortments of odds and ends (and honest-to-goodness toys!) that illustrate the principles of physics through just being neat-o.

* Cutting hundreds of pieces of wire to a specific length is its own problem, and there’s a shop-made solution for that. If you have to do a job a dozen (or a couple hundred) times over, build a jig!

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.

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.

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