A depth gauge arrived with a 3/8 inch = 9.5 mm mounting rod that fit one of my magnetic bases, but another base in my collection has a 5/16 inch = 7.9 mm clamp. Having recently rummaged through the aluminum rod stash, this happened:
The original rod at the top has an M6 thread, the drawer of random M6 screws provided suitable volunteers, and a bit of lathe work removed / shaped their heads accordingly.
The shorter rod has a blind hole, with a dab of epoxy holding the headless screw in place. Not that it matters, but the lathe held them in alignment for curing:
The longer rod got drilled all the way through, with more epoxy holding the screw, and, even with a relatively loose fit, no worries about alignment.
The longer rod gets the clamp away from the depth gauge’s base plate for better positioning:
The groove holds a length of 4 mm OD (actually 5/32 inch, but don’t tell anybody) brass tubing:
The M3 button head screws are an admission of defeat, as I could see no way of controlling the width + thickness of the aluminum slabs to get a firm push fit in the PVC tube. The screws let me tune for best picture after everything else settled out.
A little more machining opened up the top of the groove:
A short M3 button head screw (with its head turned down to 4 mm) drops into the slot and holds the slab to the threaded hole in the LED heatsink. The long screw is holding the threaded insert in place for this dry fit.
I doodled a single long screw through the whole thing, but having it fall off the heatsink when taking the rear cover off seemed like a Bad Idea™. An M3 button head screw uses a 2 mm hex key that fits neatly through the threaded insert, thereby making it work.
Butter it up with epoxy, scrape off the excess, and let things cure:
A pleasant evening at a virtual Squidwrench meeting produced the raw shape of the front end from a 1 inch aluminum rod:
Trace the outline of the LED’s PCB inside the cylinder just for comfort, align to the center, and drill two holes with a little bit of clearance:
For the 24 AWG silicone wire I used, a pair of 2 mm holes 8.75 mm out from the center suffice:
Gnaw some wire clearance in the lens holder:
Tap the central hole for an M3×0.5 screw, which may come in handy to pull the entire affair together.
Epoxy the PCB onto the heatsink with the lens holder keeping it aligned in the middle:
Then see how hot it gets dissipating 900 mW with 360 mA of current from a 2.2 Ω resistor:
As you might expect, it gets uncomfortably warm sitting on the bench, so it lacks surface area. The first pass will use a PVC cylinder for easy machining, but a full aluminum shell would eventually be a nice touch.
A doodle with some dimensions and aspirational features:
Even without a lens and blinkiness, it’s attention-getting!
The cut is just in front of the PCB and went slowly to avoid clobbering the SMD resistors very near the edge.
The cataract turned out to be crud adhered to the LED lens:
Brutal surgery removed the LED and installed a replacement:
The PCB had two 150 Ω SMD resistors for use with 12-ish V automotive batteries. While I had the hood up, I removed one and shorted across its pads to make the LED work with the 6 V switched headlight supply from the Bafang motor.
In round numbers, 6 V minus 2.2 V forward drop divided by 150 Ω is about 25 mA. The original LED ran at 35-ish mA, but it’s close enough.
Glue the lens back in place:
The bubbly stuff is solid epoxy from the original assembly, which is why removing the PCB is not an option.
The new LED is no more off-center than any of the others:
It does, however, sit much closer to the lens, due to the ring of plastic I cut away to get inside. As a result, the beam is mostly a single centered lobe with only hints of the five side lobes; there isn’t much waste light from the side of the LED into those facets.
On a typical bike, it mounts against a cable stop with the cable housing holding it in place against its other end:
The Terry Symmetry has only two lengths of housing: in front of the adjuster on the downtube and behind the stop brazed to the chainstay. In either position, the sensor would move as the shift cable flexed and (IMO) put unreasonable stress on the electrical cable running to the motor.
Yes, the Tour Easy has those same two lengths of housing, but the forward one joins a sheaf of wires & cables that barely moves.
Fortunately, the sensor fits neatly between stations 1 and 2 along the downtube, with a snippet of PTFE lIned housing holding it firmly in place, with the 3D printed battery mounting blocks including paths for both cables:
The shift cable originally ran from the adjuster in the front to the guide under the bottom bracket along a slightly diagonal path I could not possibly match. Instead, the path is now parallel to the downtube from the front adjuster:
.. to the rear block, where it angles downward over the motor to the bottom bracket:
The front block at station 1 has a Delrin / acetal bushing to align the cable with the rest of the blocks:
Yes, it’s a round peg jammed in a hexagonal hole:
Turning it from stock is well within the capabilities of Tiny Lathe™:
One of those LED spotlights may have barely outlasted its worthless warranty, but not by much, and has been languishing on the back of the bench with “Flickers hot” scrawled on its side.
The metal base didn’t respond to twisting, so I slit the threads with a cutoff wheel:
Applying the screwdriver removed the base to reveal a silicone rubber casting:
The small wire emerging near the edge of the plastic case seems to be the neutral contact to the shell, with a poor enough joint to suggest it might have been why the lamp flickered when it got hot.
Some brute force snapped the silicone off at the bottom of the plastic case and broke the two wires bringing AC to the PCB:
Digging around inside produced a debris field of silicone crumbs, broken resistors, torn caps, and various other components, with zero progress toward removing the shell:
A little lathe work converted a chunk of PVC pipe into a crude mandrel supporting the mangled case:
A few millimeters of sissy cuts released a silicone O-ring sealing the shell against the reflector:
Continuing the cuts eventually revealed the three screws holding the shell to the reflector and the two wires powering the LED:
Chopping off the screws with a diagonal cutter freed the shell and revealed the top of the PCB:
It really does have a surprising number of components!
Those three screws connected the LED panel / heatsink to the shell through the back of the double-walled reflector. More brute force peeled the outer shell away and released the panel:
Each of the 5050 packages contains a pair of white LEDs with 5.2 V forward drop for the pair, at the very low test current. They’re all in series, so you’re looking at well over 60 V total forward drop: