Wednesday, October 14, 2015

Bike Lights

I've been without bicycle lights since loaning my bike out to one of the interns at my former employer. Unfortunately, this makes riding at night somewhat illegal. As autumn wears on, the daylight is going, and the likelihood of being caught without lights after dark increases dramatically, so I decided to fix this problem.

Not long ago, I was at Cole Valley Hardware, and they had some really cheap bike lights. But then I loaned these to a friend, and it's not worth the trouble to get them back. And then I went back to the hardware store to get the lights, and all they had was the rear light. The headlights weren't available.

So rather than shell out $20 for an expensive headlight, I decided to adapt this cheapo LED flashlight I don't use very much. It came as part of a set which included too many flashlights. I had tried to do this once before using a product called "Shapelock" (also sold at Radioshack as U-Shape). But the result was super ugly. I took it off and recycled the Shapelock.

So the first step was to make a clamp which would grab the flashlight itself. This was my first attempt. I got the internal dimensions of the channel correct on the first try. The flashlight handle is basically a tapered cylinder, which I modeled using a loft operation in 123d.

 It looked reasonable on the computer screen, but when I printed out just seemed way too bulky and ugly.
So, I made a slimmed-down version. It took a couple of tries to print this correctly. The first time, I tried to print both pieces simultaneously, but the filament jammed near the end of the print. I was able to fix the jam, but the goof weakened the print and it snapped when I tried to assemble it. This motivated the previous post on preventing filament jams.

Today, I re-printed the pieces separately, and this  time they printed beautifully. To get the best finish, I printed the top piece face up with support. The support comes off easily with pliers, but leaves a jagged edge which must be filed / sanded down. I'd rather you not see that on the top-side, but it doesn't matter if it's on the interior.

I've made versions of this handlebar bracket, but my bicycle handlebars are 1.25" in diameter, rather than .9" like the motorcycles' are. So, I needed to make a slightly larger version. Also, the clamp which holds the bars in place requires that the mount be offset slightly. This one printed beautifully on the first try:

There are two tricks to assembling the clamp: one is that I use brass thread inserts from Yardley products. This allows me to use machine screws to get good clamping force without worrying that the screws will pull out of the plastic. The other trick is to use contact-cement to adhere a thin layer of rubber on the interior of the clamp.

This is both to ensure a good tight grip on the bars, and also to protect the paint on the bars when you rotate the clamp. For rubber, I just used an old bicycle inner tube, which the neighborhood bicycle shop gave me for free. One trick is to trim along the rubber seams, so that you get a nice, flat piece.

For the rear light, I didn't have to work nearly as hard. The light comes with a kindof useless clip mount, but this unscrews very easily.

I reverse-engineered the screw hole / alignment dowel pattern and whipped up this flexture clamp design, which printed beautifully on the first try. Since the seat post comes out completely, this seemed like a good way to go, rather than using a two-piece clamp.

I measured my seat-post diameter as about 1.050", decided to make the outside diameter of the clamp 1.1" just to give a little margin for error. The clamping force is provided by a #6x1/2" sheet metal screw. A 0.1" slot cut into the clamp allows the clamp to flex just enough to tighten around the seat post.

Mounting the clamp onto the light just re-uses the screw it came with. Since the mounting screw goes into the light, I had to add a counter-bore, which I chamfered so that the tapered head would snug nicely onto the light. I made a little bit of a goof, by making the mounting surface too long, but this has been corrected in the model. In order to actually screw the mounting screw on, I had to add a second hole to allow for insertion of the screw driver.

The result looked a lot more professional than I was expecting. I think the bright screw set against the dark, black plastic tends to do that.

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