Posts Tagged CNC
The original ball around the flashlight consisted of two identical parts joined with 2 mm screws and brass inserts:
Providing enough space for the inserts made the ball bigger than it really ought be, so I designed a one-piece ball with “expansion joints” between the fingers:
Having Slic3r put a 3 mm brim around the bottom almost worked. Adding a little support flange, then building with a brim, kept each segment upright and the whole affair firmly anchored.
Those had to be part of the model, because I also wanted to anchor the perimeter threads to prevent upward warping. Worked great and cleanup was surprisingly easy: apply the flush cutter, introduce the ball to Mr Belt Sander, then rotate the ball around the flashlight wrapped with fine sandpaper to wear off the nubs.
The joints between the fingers provide enough flexibility to expand slightly around the flashlight body:
I made that one the same size as the original screw + insert balls to fit the original clamp, where it worked fine. The clamp ring applies enough pressure to the ball to secure the flashlight and prevent the ball from rotating unless you (well, I) apply more-than-incidental force.
Then I shrank the ball to the flashlight diameter + 10 mm (= 5 mm thick at the equator) and reduced the size of the clamp ring accordingly, which made the whole mount much more compact:
The flashlights allegedly puts out 400 lumen in a fairly tight beam. The fairings produce a much larger and brighter glint in full sunlight than the flashlights, so I think they’re about the right brightness.
The OpenSCAD source code for the new ball as a GitHub Gist:
A pair of torchiere lamps lit the living room for many, many years:
During their tenure, they’ve gone from 100 W incandescent bulbs to “100 W equivalent” CFL curlicues to “100 W equivalent” warm-white LED bulbs. The LEDs aren’t up to the brightness of the original incandescents, but you can get used to anything if you do it long enough.
After so many years, the plastic shades / diffusers became brittle:
That’s after a bump, not a fall to the floor. So it goes.
Some casual searching didn’t turn up any likely replacements. The shade measures 14 inch = 355 mm across the top, far too large for the M2’s platform, but maybe a smaller shade in natural PETG would work just as well.
ACHTUNG! This is obviously inappropriate for the original incandescent bulbs and would be, IMO, marginal with CFL tubes. Works fine with LEDs. Your mileage may vary.
OpenSCAD to the rescue:
That’s a section down the middle. The top is 180 mm across, leaving 20 mm of general caution on the 200 mm width of the platform. The section above the sharply angled base is 90 mm tall to match the actual LED height, thereby putting them out of my line-of-sight even when standing across the room.
I ran off a short version, corrected the angles and sizes for a better fit, tweaked the thickness to fuse three parallel threads into a semitransparent shell, and …
Producing what looks like thin flowerpot required just shy of seven hours of print time, as it’s almost entirely perimeter, goin’ down slow for best appearance. The weird gold tone comes from the interaction of camera flash with warm-white CFL can lights over the desk.
If you hadn’t met the original, you’d say the new shade grew there:
It’s definitely a Brutalist design, not even attempting to hide its 3D printed origin and glorying in those simple geometric facets.
Those three threads of natural PETG makes a reasonably transparent plate, clear enough that the bulb produced an eye-watering glare through the shade:
So I returned it to the Basement Laboratory, chucked it up in the lathe (where it barely clears the bed), dialed the slowest spindle speed (150 rpm according to the laser tach, faster than I’d prefer), and slathered a thin layer of white-tinted XTC-3D around the inside:
For lack of anything smarter, I mixed 2+ drops of Opaque White with 3.1 g of Part A (resin), added 1.3 g of Part B (Hardener), mixed vigorously, drooled the blob along the middle of the rotating shade, spread it across the width using the mixing stick, smoothed it into a thin layer with a scrap of waxed paper, and ignored it for a few hours.
If the lathe perspective looks a bit weird, it’s perfectly natural: I raised the tailstock end enough to make the lower side of the shade just about horizontal. Given the gooey nature of XTC-3D, it wasn’t going anywhere, but I didn’t want a slingout across the lathe bed.
The lit-up result isn’t photographically different from the previous picture, but in person the epoxy layer produces a much nicer diffused light and no glare.
I might be forced to preemptively replace the other shade, just for symmetry, but we’ll let this one age for a while before jumping to conclusions.
The OpenSCAD source code as a GitHub Gist:
Pending more test rides, the flashlight fairing mount works well:
Despite all my fussing with three rotational angles, simply tilting the mount upward by 20° with respect to the fairing clamp aims the flashlight straight ahead, with the ball nearly centered in the clamp:
That obviously depends on the handlebar angle and the fairing length (which affects the strut rotation), but it’s close enough to make me think a simpler mount will suffice: clamp the flashlight into a cylinder with a slight offset angle, maybe 2°, then mount the cylinder into a much thinner ring clamp at the 20° tilt. Rotating the cylinder would give you some aim-ability, minus the bulk of a ball mount.
Or dispense with the separate cylinder, build the entire mount at the (now known) aim angle, clamp the flashlight directly into the mount, then affix mount to fairing strut. Rapid prototyping FTW!
For now, it’s great riding weather …
The OpenSCAD source code as a GitHub Gist:
The fairing mount must aim the flashlight generally parallel to the ground and slightly toed-in toward the bike’s frame, ideally holding the ball more-or-less in the center of its adjustment range. I eyeballed a protractor for the initial estimates and got it reasonably close on the third try:
One more skilled in math than I could define a matrix transformation between the solid model’s XYZ coordinate space and the fairing’s XYZ space, then figure the reverse transformation allowing you to convert real-world angles back to the model’s space. I winged it by setting up adjustments to rotate the ball clamp ring on all three axes around its center:
Lifting the ring upward by half its OD leaves it tangent to the XY plane, firmly embedded in the blank fairing clamp plate, and, through the magic of 3D printing, looking like it grew there.
In practice, aligning the ring isn’t too difficult. Align an eyeball along each of the mount’s axes, center a protractor on the ball with it perpendicular to the line of sight, rotate it so the baseline is level / straight-ahead / crosswise, read off the angle, then type it in. Of course you’ll get the sign wrong at least once.
For a given set of those angles, the mount looks like this:
You can determine by inspection there’s no way to orient the shape for E-Z building, although putting the plate flat on the platform has a lot to recommend it.
The outside being a spherical section, the overhangs will curl upward, so (as with the ball around the flashlight) rows of fins anchor the perimeter threads:
The fins are just under two threads wide to eliminate any possible infill, with a simple sphere chopping their tops to fit just inside the clamp:
Slic3r built support structures under the overhanging screw bosses:
It also added weird little towers that don’t come close to touching the clamp’s lower surfaces, which is why I added those fins. The automatic support should extend to one thread thickness from the bottom surface, but that’s a hard calculation to make for a spherical section represented by tesselating triangles.
After a few test rides, the whole affair seems to be both holding together and holding the flashlight, so it’s good enough for now. A twilight ride around the block may be needed for better aiming, though.
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.
A note arrived from someone who obviously couldn’t pass up an orphaned HP 7475A plotter:
The plotter I received works beautifully, except that the carousel doesn’t rotate. I found a YouTube video showing a 7475a running with the cover off, and there’s a little plastic piece – it looks like a teardrop – that advances the carousel, and is apparently part of the carousel motor assembly. Mine is missing that piece …
The keyword is Geneva drive, a wonderfully simple technique to convert one rotation of the stepper motor into 1/6 turn of the pen carousel, with no need for fancy sensors.
Back in the day, you could get the entire Pen Carousel Housing Assembly w/ Motor (PN 07475-60175) as a unit and the Carousel Motor Only (PN 3140-0687) as a separate thing, but not the Geneva drive wheel:
The cam’s drive wheel end (in inches, because early 1980s):
- 0.25 thick overall
- 0.10 thick plate under pin end
- 1.09 OD – rounded end
The pin sticking up from the cam:
- 0.154 OD (or fit to slot?)
- 0.16 tall (above base plate)
I have no good (i.e., easy + accurate) way to measure the distance from the motor shaft to the pin, but I doubt it’s critical. As long as the pin doesn’t quite whack the hub end of the slot, it’s all good:
The 0.10 plate + 0.16 pin height don’t quite add up to the 0.25 overall measurement, but that’s certainly measurement error. I’d round the pin length downward and carve the drive from a 1/4 inch sheet.
A 3D printed part would probably work, apart from the accuracy required to fit the D-shaped motor shaft. Perhaps a round hole, reamed to fit the shaft, carefully aligned / positioned, with epoxy filling the D-shaped void, would suffice. A dent in the round hole would give the epoxy something to grab.
I’d be sorely tempted to use an actual metal / plastic rod for the pin, rather than depend on a stack of semi-fused plastic disks. The pin must withstand hitting the end of the “missing” slot during the power-on indexing rotation, because turning the carousel isn’t quite a non-contact sport. Normally, though, it enters the end of the slot without much fuss:
The blocked slot sits at the bottom of that picture, with a small locating pin sticking upward just above the circular feature at the end of the arm: we’re seeing the negative of a plug inserted into the original injection mold.
[Update: It lives! ]