Bike lights, a year later

[xiphmont]

You all might remember the "spiffiest-possible indestructible bicycle lights" I made for Camilla last year. She had [well, still has] a nasty tendency to regularly destroy the small accessories bolted to her bike, lights especially. After destroying a third flimsy CatEye led bike light in a minor spill, I decided enough was enough. I don't know anyone else more deserving of... needing of... a spiffy mountain bike with good lighting, so a year ago I'd set out to make her something top shelf and indestructible.

The term "indestructible" is subject to annoying real-world constraints. Or, as Camilla recently summarized, "I suppose this is the end of your love affair with polycarbonate."

There are a few wonderful things about polycarbonate, better known as the material used to make bulletproof glass. It's flexible, clear, proof to shattering, and relatively easy to work especially by hand. It cuts like butter and is fairly strong.

Unfortunately, like many other plastics, it 'crazes' under static load. Over months or years, tiny nearly microscopic cracks will slowly spread through the plastic when it is held under stress. The stress can be any number of things. Water, surprisingly, is one; polycarbonate, like acrylic, is not actually waterproof, just mostly waterproof. It will hydrate slightly, expanding when it does so and creating internal stress. Thermal expansion and contraction will do the same. The simple act of cutting can impart alot of random stresses to the edge as well as providing the starting points for cracks. So will drilling a hole through it and bolting it down. All relevant to making bicycle lights out of the stuff, and screwing said lights down onto handlebars.

So when Camilla was barreling down Conwell in the dark... in the cold... in the rain... at somewhere between twenty and thirty miles an hour, unaware that the city public works department had removed a chunk of pavement creating a sudden two or three inch tall step up, right in the middle of the street, it probably wasn't too surprising one of the darn things snapped right across a screw hole. The front wheel didn't survive either, for whatever that's worth. Camilla was fine, by the way, she avoided crashing.

Any impact that caves the front wheel of a bicycle is going to transmit a huge shock to the handlebars, but the lights were intended to be *indestructible* not *moderately hardy* or *somewhat sturdy*. Sure, a commercial plastic light would have exploded into a zillion pieces. Still not good enough. I don't have to make things out of plastic just because it's easy to shape anymore. This affront to my skills will not stand.

First step was getting the old broken 'stalk' off the dangling light with minimal fuss and, while we're at it, removing the others toward replacing them too. If one broke, eventually they'll all break. Fortunately, polycarb is also slightly squishy, and a pair of vice grips and some brute squeezing force popped them right off the epoxy I'd used to secure them to the copper bodies of the actual lights.

A little Dremel work grinds off the epoxy ridge left behind such that there's no trouble settling new stalks into place.

The old stalks were cut freehand out of polycarb using my flimsy little Sears band saw (now deceased-- it sucked till the very last) and a Dremel. The shaping was rough at best. The new stalks are also freehanded, but from 6061 aluminum using a much nicer floor-standing industrial bandsaw, then shaped on the mill, then polished to a smooth matte in the metal finisher. A much more attractive job, much sturdier, and probably faster...

Stalks primed, painted and ready for mounting...

Run a small bead of metal-filled high temp epoxy (eg JB Weld), press on stalk, clamp, come back in a day, touch up the paint, screw down and all done!

Fully back in business and even closer to indestructible.

Comments

[twitch124.livejournal.com]

Nice!