Category: Recumbent Bicycling

With the flashlight firmly clamped inside its ball, a surrounding clamp ring holds the ball on the mount:

The solid model chops a sphere to a completely empirical 70% of the inner ball’s length (which, itself, may be truncated to fit the flashlight grip) and glues on a hull containing the M3x50 mm screws:

The complete ring looks about like you’d expect, although it’s never built like this:

The top half builds as an arch on the platform:

The uppermost layers on the inside of the arch have terrible overhang pulled upward by the cooling plastic, so the builtin support structure hold the layers downward. The preview shows they don’t quite touch, but in actual practice the support bonds to the arch and requires a bit of effort to crack off:

The ones on the right come from my (failed) attempts to build the ball hemispheres in the obvious orientation. It’s worth noting that my built-in “support” both bonds to the part and breaks off in one piece, quite unlike the pitched battle required to separate Slic3r’s automatic support structures; I think that’s the difference between the minimum feasible and maximum possible support.

Anyhow, the inside of the arch requires only a bit of cleanup with a ball mill before it clamps firmly around the flashlight ball. In the normal orientation, the space over the missing ball cap snuggles into the cleaned-up part of the arch and there’s enough friction on the remaining ball to hold it in place. If it does joggle loose, a wrap of tape should provide enough griptivity.

I started by assuming socket-head cap screws and brass inserts embedded in the clamp ring could provide enough force to hold everything together:

The head recesses into the top opening and the insert sits just below the split line on the XY plane. That turned out to be asking a lot from a pair of 3 mm knurled brass inserts, even with JB Weld in full effect, and I wasn’t at all confident they wouldn’t pop out under duress and fling the flashlight away.

Each screw now compresses the entire boss between a pair of washers and the nyloc nut won’t vibrate loose. The screws also serve to stiffen the clamp ring front-to-back, although I’m not convinced it needs any reinforcement.

I also considered splitting the ring parallel to the front, right down the middle, with screws extending through both halves:

It’d be trivially easy to build the front half face-down on the platform, but the rear would have only half the surface area bonded to the plate against the fairing, which seemed like a Bad Idea. Worse, I couldn’t figure out how to align the rear half on the plate with enough room for the nuts / inserts / whatever and alignment space around the front half.

A flashlight used as a daytime running light must point generally forward and an actual bike headlight must light up the road, so it must sit on an az-el mount. My old bike helmet mirror mount had actual vertical and horizontal joints:

Every doodle along those lines seemed too big, too fragile, too fiddly, or all at once.

Living here in the future, though, we can produce (crude) ball joints to order:

That’s an early version of the outer mount using threaded brass inserts.

The ball around the flashlight separates along the obvious plane of symmetry, with a 2 mm socket-head cap screw and brass insert on each side. I tried printing the hemispheres convex-side-up with hand-hewn support structures inside:

The huge overhanging sections parallel to the axis didn’t bond to the supports, curled upward, and began nudging the dangling Z-axis homing switch actuator. This wasn’t a completely wasted effort, though, as similar support structures came in handy for the outer clamp ring.

Flipping the hemispheres over so they printed U-channel upward didn’t work much better, even sitting on a flat section to eliminate the absurd part of the overhang. This view shows one hemisphere with the missing cap:

Flipped over, the flat surface bonded perfectly to the platform, but the overhang still warped as the upper layers cooled and pulled the perimeter upward:

Because normal support structures don’t contact the outer surface, I added fins to the model to hold the perimeter (almost) flat until the outer walls became sufficiently vertical to stop warping:

They’re fearsome hedgehogs in person:

The grip diameter determines the sphere diameter, as the sphere must have enough meat next to the grip to hold the screws and inserts. Rather than have the diameter different for every flashlight, I set it to the maximum of 45 mm or the actual diameter, which means all the flashlights in my collection have a common ball size. The hemispheres on the right have flattened ends to accommodate flashlight grips shorter than the sphere’s final diameter, achieved with a pair of intersection() operations lopping off the protruding bits:

Because the fins extend from resolutely convex surfaces, I snipped them off with flush-cutting pliers, reamed out the holes, epoxied the inserts in place, assembled the ball, and introduced it to Mr Belt Sander.

Protip: don’t hold the ball with your finger through the hole. It will eventually fly off under the workbench and it’s better if it doesn’t break your finger in the process.

A somewhat rough outer surface turns out to be an advantage, not a liability, as the clamp ring around the ball must hold it against the normal (and unusually severe) vibrations found on a bike.

The inner cylindrical section is smooth enough to require a wrap of tape around the flashlight grip to anchor it in position. The tape adheres to the flashlight and squishes into the ball’s layer lines, even under mild pressure from the 2 mm screws. The outer clamp ring applies compression to the ball, so the tiny screws need not withstand much force at all, which is a good thing.