Archive for June 23rd, 2010
The plastic-ball-in-plastic-socket joint found in bicycle mirrors seems to fail after a year or two of constant use. These are some doodles & thoughts about building a small, robust, adjustable joint.
A bike mirror needs two ball joints:
- at the helmet mount to put the mirror in the proper spot
- at the mirror to align the image
A flexy boom can replace the helmet joint, although rotation around X (pitch) is still handy.
A flexy mirror mount can replace the mirror joint, but it must also be compact.
Without heroic measures, the range of travel for a ball joint isn’t all that much.
How to make a ball? Anneal & drill a standard ball bearing for a wire shaft? Solder onto chrome steel? CNC mill the end of a bar in a rotary table?
How to make a socket? Some of that low-temperature themoplastic might be useful. Mold it around the ball, slit radially, and squash it in a circ clamp?
How to adjust? Circumferential clamp around the socket or pull the whole socket into a wedge? Radial cuts through the socket to allow compression or depend on plastic/elastic deformation?
How much friction? You want it stiff enough to hold position in a strong wind and easy enough to reposition. You definitely don’t want grub screws or fiddly knobs!
The doodles are all far too complex, some are absurd, one can’t be built (at least by me), and I’ll probably end up using some bendy wire anyway.
Something of this may be useful in another project … and now I can throw out that scrap of paper.