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This repair was not completed at a Repair Café or Fixit Clinic, but it was kind of interesting so I’m writing a post about it. Machining often involves arithmetic on very precise numbers. This is very tedious, so having a small calculator is very helpful. Being of a helpful nature, my school’s machine-shop has a few calculators, but nearly all of them are broken for some reason or another. This post is about fixing one of them. The calculator in question is a Casio FX-115S. It is a scientific calculator powered by either a solar panel or a button-cell battery.…
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Part of my bicycle-lighting project involved crimping a splitter cable to split the output of the dynamo to the front and rear lamps. I used a DuPont connector for that because I had recently bought, after 4 years of consideration, a proper DuPont crimper. The input and output wires were 24 AWG solid wires with an insulation diameter of about 1.3 mm. A DuPont crimp actually consists of 2 crimps, one onto the stripped wire, and another onto the insulation for strain relief. The biggest challenge when attempting to crimp 2 wires is getting the insulation of both properly into…
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Recently finding the need to bike home in the dark, and not wanting to regularly charge a battery-powered light, I decided to buy a used bicycle dynamo (for $40) to power a front and rear bike light. The dynamo is a bottom-bracket dynamo, which means it’s meant to be mounted on the bottom bracket (where the pedals are mounted) and is driven by the tire tread. This contrasts with bottle dynamos which are driven by the sidewall of the tire, potentially wearing out the sidewall. There was no space to mount the dynamo on my bottom bracket, but thankfully it…
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I recently bought a used cross-slide vise on craigslist for $35. It is a machinist’s vise mounted on two ways at right angles, with leadscrews controlling the vise’s movement along each way. It’s meant to be used on a drill press so holes can be located in the same manner as in a vertical milling machine. The vise is also useful since it allows the piece to be moved under the spindle without loosening and re-clamping it as in a normal machine vise. The vise was originally bought at Harbor Freight, a store known for affordable but low-quality tools. …
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This event took place at the San Mateo Library. I mainly spent the 3 hours working on a broken IBM Selectric typewriter; I’ve had some experience restoring manual typewriters. The owner had taken it to a repair shop because the keys were a bit sticky, and it had come back broken. It appears the repairman had put a lot of oil and grease in the typewriter, which had gummed some things up. Wikipedia has a detailed description of the Selectric’s mechanism here, though it’s rather meaningless unless you have it in front of you to look at. So …
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This Fixit Clinic occurred at the Maker Nexus in Sunnyvale. The first item was a Saeco Vienna Plus espresso machine. It automated the entire brewing process, including grinding and measuring the coffee, dispensing it into the “brew group” (the removable assembly where the actual brewing takes place), tamping it down, forcing water through the grounds, and ejecting the puck. Essentially, it worked as follows: A burr grinder both ground the coffee and pushed it into the dispenser. The dispenser was a small chamber with a trapdoor in the bottom to release the coffee into the brew group, and one movable…
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Soldering iron tips are made of copper plated with a very thin layer of iron. Unfortunately, this plating can oxidize if you don’t clean and “tin” it (that is, coat it with solder to protect it), and this can be very annoying because the oxidation is difficult to get off and prevents the solder from wetting the tip. There are a number of ways to get stubborn oxidation off. The recommended way is use some sort of tinning compound designed especially for this purpose, like sal ammoniac. Over the years, I’ve tried a few alternative methods, mostly without success. First…
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A spinning gyroscope can balance on a pivot, defying gravity by remaining horizontal while resting just on the tip of its axle. Instead of falling off the pivot, the gyroscope circles around it. The explanation for this amazing feat lies in the effects of precession. Like all other objects, the rotating wheel of the gyroscope is subjected to gravity. However, as long as the gyroscope spins, precession overcomes gravity by transforming it into a force that causes the gyroscope to circle instead of falling. The Way Things Work by David Macaulay and Neil Ardley At the suggestion of my physics…
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I made a gyroscope. Part of that involved casting 12 zinc weights to go around the rim of its rotor, which gave me a lot of practice ramming and pouring molds, and I learned a lot. Firstly, for my extremely rudimentary dirt-bonded sand, the right moisture level is just enough to turn the sand noticeably dark, indicating that the clay is fully wetted with water, but not so much that it sticks to the rammer. While many hobbyists on the internet recommended using a peen-shaped rammer to better compact the sand, I found it easier to simply ram the …
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This Repair Café took place at the Mountain View Senior Center from 11:00 AM to 3:00 PM. First, I worked on an Instant Pot® Vortex® Plus 10 Quart air fryer that wouldn’t power on; the owner said it had just stopped working one day with no major incident preceding it. After some light disassembly (prying off the top vent and removing the top cover), we found that the bimetallic thermostat had been tripped and needed to be manually reset with a little button. I’m not sure why the air fryer was designed the way it was, with a difficult-to-access manual-reset…
