The Smell of Molten Projects in the Morning

Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.

Author: Ed

  • Bike Helmet Mirror Re-Repair

    Socket with brass reinforcement
    Socket with brass reinforcement

    The front ball joint on the mirror on Mary’s helmet loosened enough that the mirror blew out of position every time we got up to a decent traveling speed. I’ve repaired these mirrors several times before; they’re plastic and tend to fracture / wear out / break at inconvenient moments.

    The first pic shows the mirror (the black surface is reflecting the dark floor joists overhead) with an old blob of epoxy that repaired a break in the outer socket. The socket originally had stylin’ curves joining it to the mirror, which proved to be weak spots that required epoxy fortification.

    This time the socket split axially on the side away from the mirror, which released the pressure on the ball socket that seats into it. I found a chunk of brass tube that fit snugly over the socket, then carved some clearance for the existing epoxy blob. The key feature is that the tube remains a ring, rather than a C-shaped sheet. to maintain pressure around the socket.

    Clamping the reinforcement ring
    Clamping the reinforcement ring

    Here are the various bits, with the reinforcing ring clamped in place. I coated the socket exterior with JB Weld epoxy, slipped the ring in place, and tapped it down with a brass hammer to seat flush with the front face of the socket. That left gaps between the socket opening and the tube that I eased more epoxy into with an awl. A bit more epoxy around the exterior smoothed over that ragged edge.

    The strut at the bottom of the picture ends in a ball joint held by a socket that slips into the mirror socket. The loose brass ring above the mirror is some shim stock that I added some years ago to take up slop between the ball socket and the mirror socket and tighten the ball joint. I suppose that pressure eventually split the outer socket, but so it goes.

    Repaired mirror joint
    Repaired mirror joint

    The clamp squished the outer socket enough to snug it around the ball socket, so when I reassembled the mirror it was fine. To be sure, I dunked the ball in my lifetime supply of Brownell’s Powdered Rosin for a bit more non-slip stickiness.

    I have a box full of defunct bike helmet mirrors, dating back to those old wire-frame square mirrors that clamped onto the original Bell helmets. The newer plastic ones just don’t last; we ride our bikes a lot and even fancy engineering plastic isn’t nearly durable enough. A few bits of metal here and there would dramatically improve the results!

    I’m going to build some durable wire-frame mirrors, but … this will keep us on the road for a while. I suppose I should make a preemptive repair on my helmet mirror while I’m thinking of it…

  • Why We Use Bicycle Tire Liners

    Bike tire puncture
    Bike tire puncture

    A glass chip gashed the front tire of my bike a while ago, but the slit didn’t cut the Kevlar belt underneath and I let it slide. The pre-ride check before our 50-mile day trip to Old Rhinebeck Aerodrome showed that things had gotten worse (the tire liner was peeking out through the belt), so I replaced the tire before we set out.

    Tire liner abrasion
    Tire liner abrasion

    This pic shows that the tire liner was doing its job, although it was slightly abraded and had picked up some road grit. The tube had a barely visible mark.

    I generally use fluorescent green Slime tire liners, but this one is a competing brand I picked up a while ago. Not much to choose between the two, although I think Slime liners have a better edge taper and tend to be more flexible.

    Notice the other nicks and gashes in the tire tread? We run Schwalbe Marathons on the rear and Primo Comets on the front, both have Kevlar belts. Flats are not a problem any more, even with plenty of sharp road debris; I replace the tires every two years or so when the tread wears smooth or a major gash worries even me. My rule of thumb: when I can see the liner, it’s time to replace the tire.

    Tread gash - Schwalbe Marathon
    Tread gash – Schwalbe Marathon

    There are riders who argue for very lightweight tires on the basis of performance: better acceleration and lower rolling resistance. I’m willing to trade all that off against not having to dismount a tire by the side of the road…

    [Update: Plenty more posts on this general subject, with graphic illustrations of tire damage. Search for liner and you’ll find ’em.]

  • Bike Rim Reflectorization

    Bike wheel with retroreflective tape
    Bike wheel with retroreflective tape

    Here’s a quick-and-easy way to improve the odds of your arriving home safely after dark: add snippets of retroreflective tape to the inside of the rims on your bike.

    Do half the rim in one color and leave the other half untaped (or taped in a contrasting color) so that the rim flashes as the wheel rotates. I originally applied orange tape, of which I have very nearly a lifetime supply, then added white when I got a sheet as part of a surplus deal.

    At 15 mph the 20-inch front wheel blinks at about 4 Hz, which is wonderfully attention-getting. The rear wheel, a more common 700C size, blinks at 3 Hz.

    It helps to measure the space between spokes, then set up a template to cut all the tape pieces the same length. Wipe the big chunks of dirt off the rim, then remove the remaining grunge with alcohol so the tape actually sticks.

    New York State vehicle law considers reflectorized tires as equal to those in-the-spokes reflectors, which is a Good Thing.

    The more you look like a UFO after dark, the less surprised the drivers are and the less hassle you get.

  • Keeping the Screws in Sherline Hold-Down Clamps

    A small improvement: add a snippet of heat stink shrink tubing to the screw in the L-shaped hold-down clamps and the screw won’t go walkabout in your tooling widget case.

    Make it the same length as the distance from the clamp to the surface and it’ll remind you how far to screw on the T-nut when you swap the clamps from tooling plate to milling machine table.

    The Sherline Mill Vise (PN 3551) comes with a set of clamps. They’re also available separately as the 4-Jaw Hold-Down Set (PN 3058).

  • Trimming Voltage Regulators by Stacking SMD Chips

    LM317 Regulator (Partial) Schematic
    LM317 Regulator (Partial) Schematic

    Quite often, the values you need for voltage regulators, like the venerable LM317 and its ilk, don’t work out to anything you have in your parts bin. What to do?

    One of the really nice things about SMD resistors is that you can stack them up without much effort. That parallels their value, so you can only make the final value smaller than any of the stacked resistors, but we can work with that.

    The schematic shows part of a multi-voltage power supply for the EPROM programmer I mentioned there. Normally you use a 240-Ω resistor between the Output and Adjust terminals, but anything in that range will work fine. Alas, when I went to the parts bin, that’s the value I didn’t have any of.

    But, having recently acquired an assortment of 60-some-odd 1% chip resistors, 100 to the bag, I had enough raw material to make it work. In fact, the values in the schematic reflect the parts on hand, which is how it sometimes happens.

    A pair of 499-Ω resistors in parallel gives you 249.5 Ω, close enough to 240 (and shown as 250 because that’s only 0.2% off). Plug that value and the desired voltages into the LM317 equation to find the other resistors:

    12.5 V = 1.25 * (1 + R / 250)

    R = 250 * ((12.5 / 1.25) – 1) = 2250 Ω

    If you happen to have something close to that in your parts heap, great. I didn’t, and a stock 2200 Ω 5% resistor would produce 12.25 V; a bit lower than I wanted.

    Three sets of stacked chip resistors
    Three sets of stacked chip resistors

    This pic shows the solution: stack some SMD resistors to get the right value.

    To make this work easily, you need a calculator that has a reciprocal (1/x or x-1) key. My ancient HP-48 does that, natch, but both of the Official School Calculators our daughter uses has 1/x as a shifted function. Your mileage will certainly vary.

    Anyhow, the reciprocal of the resistance of two parallel resistors, RA and RB, is the sum of their reciprocals. Got that?

    1/R = 1/RA + 1/RB

    If you know the total resistance R that you want and one of the resistors RA, then you find the other resistor RB thusly:

    1/RB = 1/R – 1/RA

    In order to get 2250 Ω, I started with the next higher value in the assortment, 2740 Ω, and turned the crank:

    1/RB = 1/2250 – 1/2740 = 79.4809E-6

    RB = 1/79.4809E-6 = 12.58 kΩ

    As it happens, the assortment didn’t have that value, either, but it did have 15 kΩ. The parallel resistance of 2740 and 15 k is:

    2317 = 1 / (1/2740 + 1/15000)

    So turn the crank one more time to find the third resistor RC:

    1/RC = 1/2250 – 1/2317 = 12.814E-6

    RC = 78.04 kΩ

    Well, that isn’t one of the values I have either, but I do have 82.5 kΩ. The parallel value of those three resistors is:

    1/R = 1/2740 + 1/15000 + 1/82500 = 443.75E-6

    R = 2254 Ω

    Which is 0.1% off the desired value. Close enough.

    Actually, it won’t be nearly that close, because the 2740 Ω resistor can be off by 27 Ω either way. If you really care, measure the actual values and feed those into the equations. If, of course, you can measure resistors better than 1% and you don’t care about temperature effects and suchlike.

    This is appropriate for one-off projects and prototypes, not production runs, but it’s a handy trick to keep in mind. If you want to be fancy, you can lay the circuit board out with parallel resistor tracks and make it look like you knew what you were doing all along…

  • Pressure-washing the Gas Grill: Mind the Overspray

    The instructions for our Weber gas grill would have us lavish more care on it than we do on our car, which isn’t actually saying much. Nonetheless, once a year I gotta clean the crud out, whether it needs it or not, because not even I believe heat kills that stuff.

    Used to be, that was a thoroughly disgusting job of hand-scraping carbonized gunk and scrubbing gooey muck in cramped quarters. Having acquired a pressure washer, cleaning the grill is almost enough fun that I might do it more often. It even gets the mildew (or whatever that schmutz might be) off the wood handles & platforms, which I would have bet was impossible.

    Pressure washer side effects
    Pressure washer side effects

    However, if you’re even a teensy bit fussier than we are about the looks of your castle, you might want to not lay the grates & “flavorizer bars” on the driveway to blast ’em clean. Turns out that the overspray strips the grunge right out of the top layer of asphalt, leaving a white trail behind.

    Looks a lot like those Nasca peteroglyphs, doesn’t it?

    The pressure washer does a great job on the white resin plastic chairs, too, which go from really grubby to chalk-white in one pass.

    Can’t imagine how I got along without it…

    Memo to Self: Next time, use the sawhorses.

  • Red Filter for White LED Bike Headlight

    White 5-LED headlight
    White 5-LED headlight

    As I mentioned there, we have white LED bike headlights clamped to the amateur radio antennas on our bikes, facing rearward to eliminate the “But, Officer, I didn’t see him” line from the accident investigation. That works fine during daylight hours, but it’s rather blinding after dark and, in any event, taillights are supposed to be red (after 1 Nov 2009, they may also be amber).

    The easiest way to get that result, without having to tote along Yet Another Light, is to slip a red filter over the white LED lens. This dramatically reduces the light output, because the yellow phosphor used to get white light out of what’s basically a blue LED doesn’t emit much energy in the red end of the spectrum, but it’s plenty good enough to be seen from the requisite 300 feet.

    Amber filters would be a much, much better match to the phosphor and I’ll use them next year when they’re legal.

    For what it’s worth, we’ve discovered that the more we look like UFOs after dark, the more clearance we get. The bikes are extensively reflectorized and lighted, plus we have reflective arm and leg bands. If somebody hits us, it’s because they did it intentionally; that’s usually the story with drunks and punks, alas.

    Red filter components
    Red filter components

    I cut two transparent disks from ordinary electronics packaging material, plus a red disk from the Primary Red filter material mentioned there, stacked them on the headlight, and fired some big heat stink shrink tubing around them. The tubing extended maybe 3 mm past the end of the headlight and shrank into a neat lip that matched the bezel around the lens.

    The tool to have for this sort of job is an Olfa Compass Circle Cutter. It leaves a pin prick in the center of the circle, but if you’re gentle that won’t be a problem in this application.

    The shrunken tubing will be exceedingly difficult to pull off the headlight, so you may want to wrap a layer of tape around the bezel before shrinking. Peel the tape off when you’re done and the tubing will have a few mils more clearance.

    No adhesive on earth will stick to both the polypropylene disks and the heatshrink tubing, but you can try silicone snot if you want. I made the disks just slightly larger than the bezel so that the tubing captures them as it shrinks. These things spend much of their lives in a ziplock baggie, so durability isn’t an issue.

    Red filter installed
    Red filter installed

    In any event, the filter looks like this when it’s installed. Because of the odd way I mounted the headlights, the side lenses aren’t visible (and they’re white, not red), but we have plenty of other light visible from the side.

    For the straight dope on current NYS bicycle laws, go there, click on the “Laws of New York” link, search for “bicycle”, then click on section 1236. It’s New York’s idea of a useful Web interface: get over it.

    The bezels on our lights are beginning to crack, so it’s probably time to start thinking about a killer street-legal day/night amber taillight. High intensity LEDs are dirt cheap these days…