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WAYWO Bronze, Microscopy and 3D Printing [1]
['This Content Is Not Subject To Review Daily Kos Staff Prior To Publication.']
Date: 2023-12-17
Fused Deposition Modeling (FDM), 3D printing. It’s actually plotting though there are machines now that print, laying down an entire layer at a time instead of squirting molten plastic from a nozzle dragged over the previous layer.
I got my 3D printer in late February just before the covid lock down. My used clarinet came months later. Oh yeah, right, the clarinet. What ever happened to that?1
For two years I pretty much just printed crap. I filled two grocery bags full of plastic prototypes perfecting that crap. Some useful things came out of it. A large set of small drawers, a project box, a stand inside an etching tank, a tool designed to reach an inaccessible wingnut and tighten it, a thing for work. The latest conglomerate of camera and telescope I tied together with printed plastic.
Through said telescope-camera conglomerate.
Long Wavelength Infrared (LWIR) image of Zipper’s grand squirrel.
If you haven’t been following along in the WAYWO comments, I’ve been making bronze from rock. Smelting copper from malachite and tin from cassiterite. I’ve made many small samples of various proportions searching for alloys to use to make “a thing.” A dagger, a bronze age hammer and anvil, an "I don’t know what," yet.
A mistake I made alloying a sample led to the discovery that high tin bronze is golden if quenched in water immediately upon solidifying, but grey-ish silver if kept hot with a torch and cooled slowly. A raging fire, pixie dust and an incantation, and you've got alchemy.
The color depends on how you cool it. The gold cooled quickly, the grey slowly.
I wanted to know what was going on.
I started by seeing if there was a density2 difference. To do that I went to Thingiverse, one of a few large depositories of free stereo-lithographic drawings. These files describe three dimensional shapes that are used in 3D printing and animation. Over a decade’s worth of contributions from people around the globe. Tens of thousands of things, hundreds of thousands of drawings, free to download, free to print. If you can, please tip the designer.
A very early iteration of the density measuring apparatus.
Off to Thingiverse I trotted to download a density measuring apparatus. It was clear that the design wouldn’t work well with my scale so I redesigned the apparatus using Blender, an advanced free 3D drawing and animation program.
With a workable rig printed I set about weighing the samples and improving the mechanism. Hours upon hours upon hours of measuring and remeasuring with careful attention to detail to obtain a single number, plus or minus. Does it get any better than that?
My samples’ densities didn’t match accepted values. They were low. Operator error I surmised without really thinking it through. Bronze is prone to porosity3. A product of the inverse steam reaction. It’s clearly visible in the micrographs and I’m well aware of it. Swiss cheese metal, of course it’s less dense. Moving on.
Through a dirty microscope the "polished" surface of 23% tin bronze not twenty three and a half. When I created this slide I mixed up in my mind the half with the twelve and a half percent tin alloy that I made first. This alloy sample I made second. Wisely, when I cast each sample pair I photograph them with the their tin percentage label.
Metal is a granular crystalline solid. The grains can be seen when the metal is polished and etched and under a cross polarizing microscope (with the correct etching solution) they’re pretty4. Off to Thingiverse. Nope, nothing. I booted Blender.
Same alloy, initially the same piece of metal, (23% tin bronze) cooled differently. Glued, sanded, polished, and etched with dilute sulfuric acid (not the best etching solution) to make visible metal’s granular nature. The larger piece was always the one quenched.
This was printed in several pieces and glued together. 3D printing involves choices. One is between glue and spending hours pulling off pieces of “support” while trying not to damage the printed part. Overhangs need to be supported.
Me in 2005 getting ready to cast a small test sample of speculum.
I started my making of a cross polarizing microscope by printing parts less than an inch around that half fit inside a so-so quality usb microscope. I got pretty far along too but I couldn’t assemble it. I’d ruin another piece of plastic polaroid every time I tried. The so-so quality of the microscope encouraged me to follow a different path.
I’ve worked with bronze before. Almost 20 years ago I made the alloy Herschel used to make his telescope mirrors and made a mirror and a herschelian telescope with it. Speculum, 2/3rds copper and 1/3rd tin by weight looks like a modern mirror when polished and shatters like glass when dropped. All bronze is brittle. Speculum particularly so.
When I did this before, examined grain structure, I used a microscope from the early 1970s. Somewhere in my hoard of obsolete scientific instruments there was an inverted metallurgical microscope. It was a foot from where I thought it was. That’s some “meant to be” right there. Most of the other bits I’d needed were nowhere to be found. I did find the light source and fiber optic cable.
I needed to couple the microscope and my camera. At Thingiverse I downloaded an E-mount body lens adapter. In Blender I sliced off the bayonet, the part that locks to the camera to go with what I drew, the part that slides into the microscope. I printed them and glued them together. Neither part fit. This is not uncommon with 3D printing. Plus or minus a tenth or two of a millimeter when attaching to the modern machined world can mean it doesn’t fit. A file and sand paper got them close enough to force. More incremental improvements for the the next iteration.
A piece of self adhesive plastic polarizer was stuck to the shelf just inside the bayonet.
The light source is nearly 50 years old. A 24V 150W bulb and a fan that rattles the house. I’d previously coupled the fiber optic to it with a drilled and whittled piece of doweling now long gone. The replacement took two minutes to draw and 45 seconds to print. 3D prints aren’t generally that quick. More often it’s hours or even days. My longest print was 37 hours. I don’t remember what it was but I’m pretty sure it got recycled.
YouTubes
My model printer.
Same model, different presentation.
Also the same model pushed past its limits.
I wasn’t happy with the light source. The fan annoyed me. As it happened I’d just received the gift of an ultra bright LED flashlight from an old friend. It has a big fat lens on it and by pulling it out and pushing it in it can be focused. Coincidentally I also had a big fat lens that was nearly identical in size and shape and best of all I knew where it was. Together they form what in optics is called a condenser. Off to… oh well, Thingiverse doesn’t have everything, Blender.
This is the second iteration of the light source. I’m still using it. The box in the middle is a stand-in for the microscope. The “condenser” is visible on the right in the see-thru drawing.
The other end of the fiber optic needed a coupling to the microscope which would hold a piece of ground glass to disperse the light and a polaroid that could be rotated. It can be seen in the drawing above and below attached to the microscope stand-in. This is its forth iteration. I’m still using the third.
The lens depicted on the right is part of the microscope’s condenser.
I redesigned the microscope-camera coupling to use a high quality polarizer also mounted on a rotatable stage.
The polaroid carrier on the right in the foreground removed from inside the coupling is knurled to lower friction while still providing a close fit.
The polaroid carrier handles are aligned with the polarizer. Raised indicators on the couplings can be used to measure changes in angle plus or minus a degree.
All along the way I’ve been taking micrographs of the samples’ grain structures. The pictures have gotten better as the setup has evolved. What I was happy with initially is unacceptable to me now and there are more changes and additional functionality I want to add. Eventually I’ll print it all in a more stable material.
Quickly cooled 20% tin bronze under a cross polarizing microscope. On the left the polarizers are aligned. On the right, crossed.
Slowly cooled 20% tin bronze under a cross polarizing microscope. On the left the polarizers are aligned. On the right, crossed.
Most commonly FDM is done with PLA (Poly Lactic Acid) but it’s not a stable plastic. Made from corn starch it breaks down. An epoxy coating will preserve it. There are other plastics that print. For example the common and resilient plastic ABS. It stinks and it likes to rip itself off the print bed during the print. Forever plastic, PTEG, what’s used to make soda bottles, can also be printed. It’s difficult to use though. It’s stringy so the prints aren’t clean and inter-layer adhesion can be an issue. It will also rip itself off the bed. The plastic shrinks as it cools which creates stress in the lower layers. This has the effect of pulling up sides and corners. Sharp corners are the worst. I’ve developed hacks to mitigate the problem. Success varies. Printing beds are often glass and usually heated to help the plastic adhere. I print on a cold bed to save the planet or possibly because the heater broke and I haven’t fixed it.
PLA prints exceptionally well. It’s tolerant of common condition issues that other materials aren’t. If it doesn’t need to last, PLA is the best choice. If it does need to last and a layer of epoxy doesn’t get in the way, PLA is still the best choice.
Coated in epoxy it’s been sitting in a tank of ferric chloride for ten months and it’s still kicking.
Successfully 3D printing a part is not nearly as easy as it should be. There are a large number of issues and several variables that need to be understood. It’s easier on a high end printer. They typically start at over $1000. My printer was $189. It’s also tiny but these parts are small and I’ve learned how to cut designs into pieces for printing then interlock and/or glue them together.
In my next WAYWO installment I’ll present what I’ve learned about the various bronze alloys I’ve made. Hopefully I’ll have cast something by then or at least made a bronze age mold to cast it in.
1) For six months, six days a week for an hour without fail I practiced the clarinet. I was as good as any third grade clarinetist out there. Okay maybe not any, but most, well a lot, some, I wasn’t the worst.
2) Density is mass per unit volume. Water is assigned a density of one gram per centimeter cubed. Hence the difference in grams between something weighed while suspended in water and it’s weight in air is the unit volume in cubic centimeters. Density is the weight divided by the difference between the weights.
3) There are ways to minimize porosity and I will when I start casting objects. It’s not clear if the ancients knew these methods but the presents of other metals in some ancient bronze implies they may have.
4) I will and have gone out of my way, not to accomplish some lofty scientific goal but rather to make a pretty picture.
Welcome to What Are You Working On? where we talk about (and often display) our handiwork, whether yarn and fabric crafts, woodwork, metalwork, art, or anything else “crafty”. What Are You Working On?
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