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Introduction An essential idea in finite element modelling (FEM) is convergence, the idea that as you make the simulation more and more lifelike, its results will converge to the real-life stress state. In most simulations, which mainly use single-point or rigid-body constraints, the main variable that must be converged is element size: as you make the elements smaller and smaller, the simulation will become truer and truer to reality. In this case, the procedure to obtain convergence is fairly simple: run successive simulations reducing the element size each time — for example, by halving it until the results — …
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I’ve been wanting to make a die filer for some time now. It is a power-driven file that allows you to easily cut complex shapes. Die filers are not meant for a very high material-removal rate; rotary files and cold-chisels exist for that purpose. Design Parts of the Die Filer The file is run up and down on a “filing shaft”, which is supported by a “top bushing” and a “bottom bushing”. A “chuck”, consisting of a steel sleeve and set screws, couples the file and filing shaft. The filing shaft is driven up and down with a scotch-yoke mechanism,…
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This Repair Café took place from 11:00 AM to 3:00 PM at the Tzu Chi’s Northwest Region Office. Tzu Chi is a humanitarian organization whose members are Buddhist, but who do not preach to those they aid. I worked first on a Panasonic toaster oven. It had 5 heating elements: 1 clear quartz element and 2 diffuse quartz elements on top, and 2 tubular elements on the bottom. The diffuse quartz element consisted of a nichrome wire in a translucent quartz tube, emitting IR at a longer wavelength and lower intensity than the clear element, which had a tungsten wire…
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I’d previously done some experiments trying to anodize aluminium with household chemicals, avoiding the need to buy sulfuric acid. The only process that succeeded was to make sulfuric acid by the electrolysis of Epsom salt (magnesium sulfate) in a partitioned electrochemical cell, and then use the sulfuric acid for anodization in the usual way. However, the electrolysis was very inefficient and slow, and is not really applicable for anodizing any appreciable quantity of parts. So when I was recently given the opportunity to anodize and dye some parts for my school’s robotics team, I abandoned my initial goal of …
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With only a center punch and drill press, it can be very difficult to drill small, straight holes. Though medium-sized drills can self-center parts by shifting them around till the center-punch mark is exactly aligned with the spindle, smaller drills tend to just deflect and drill an angled hole. To overcome this, a short, stiff “spot drill” is used before drilling to create a new divot, exactly aligned with the spindle, obliterating the old center-punch divot and taking out any misalignment it might have had. Locating large holes accurately can also be difficult, since the large chisel-shaped tip of the…
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In Which I Am Nerd Sniped Some time in late 2024, I overheard a classmate talking about anodizing aluminium, for the purpose of laser-engraving it. They were interested in how it might be done at home. I understood the concept — using electricity to grow a thick oxide layer — and I wondered if it could be done with household chemicals. Of course, I had to try it myself, so I pursued the project on and off for the next few months. Introduction Aluminium is an incredibly reactive metal, but its oxide is inert and durable. The thin layer of…
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“The Vernier Caliper… may be used for accurate settings of dividers and trammels. Near the zero mark on the beam is a tiny indentation in the center of a small circle, and on the sliding jaw is another small cone-shaped mark. Set the vernier to the dimension required and then adjust the points of the dividers or trammels, by “feel” or with the aid of an eyeglass, exactly in the two marks.” — Machine Tool Operation, Part I, Fourth Edition, by Burghardt and Axelrod Unfortunately, not many vernier calipers today retain this feature, since the manual lay-out (i.e. scribing …
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I previously used my drill press as a strength tester. Now, with two modifications, it can grind spade drills! Modifications This tool grinder works by mounting a Dremel rotary tool in a cross slide vise and a tool in the drill chuck. Column Extension In some cases, tilting the table (discussed later) caused the original column height to be inadequate after mounting the cross slide vise and Dremel. Looking online I saw that people recommended extending the column with a length of automotive tail-pipe, so I measured my column, and quite luckily found a pipe at my local auto …
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When a piece of dried clay is heated sufficiently, the water that is chemically bound to it is irreversibly driven off, and the clay particles bond covalently to each other. After this, the clay will no longer return to the plastic state if it gets wet. As it turns out, the temperature needed to dehydrate clays can be significantly lower than their firing temperature. According to this paper, it is between 400 °C and 600 °C for kaolins, but even lower for smectites — from 200 °C to 300 °C. Since the clay from my backyard is smectic, I was…
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A common flux in soldering is zinc chloride solution. It is supposedly quite effective, though its corrosiveness makes it unsuitable for electronics. I tried using it as a tip cleaner for soldering irons that had oxidized to the point where they couldn’t be tinned with rosin-core solder. Zinc chloride (ZnCl2) is easy to make by yourself by dissolving zinc (Zn) in a jar of muriatic acid (HCl, 10M). The reaction was very vigorous for the first few minutes; the glass jar got noticeably warm, and steam came out of the jar. After a few hours I could still …
