The Smell of Molten Projects in the Morning
Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Mary persuaded the squash vine to run along the top of the garden fence, where it would get good sun, stay out from underfoot, and produce what we call aerosquash:
That bright green spot is a misplaced tree frog:
Well, maybe it’s the same frog we’ve seen elsewhere; it’s hard to tell with tree frogs.
Not everything green is froglike, though:
That one got dealt with … harshly.
The red-dot pointer on the OMTech laser cutter has the same problem as my laser aligner for the Sherline mill: too much brightness creating too large a visual spot. In addition, there’s no way to make fine positioning adjustments, because the whole mechanical assembly is just a pivot.
The first pass involved sticking a polarizing filter on the existing mount while I considered the problem:
The red dot pointer module is 8 mm OD and the ring is 10 mm ID, but you will be unsurprised to know the laser arrived with the module jammed in the mount with a simple screw. Shortly thereafter, I turned the white Delrin bushing on the lathe to stabilize the pointer and installed a proper setscrew, but it’s obviously impossible to make delicate adjustments with that setup.
Making the polarizing filter involves cutting three circles:
Rotating the laser module in the bushing verified that I could reduce the red dot to a mere shadow of its former self, but it was no easier to align.
Replacing the Delrin bushing with a 3D printed adjuster gets closer to the goal:
Shoving a polarizing filter disk to the bottom of the recess, rotating the laser module for least brightness, then jamming the module in place produces a low-brightness laser spot.
The 8 mm recess for the laser module is tilted 2.5° with respect to the Y axis, so (in principle) rotating the adjuster + module (using the wide grip ring) will move the red dot in a circle:
The dot sits about 100 mm away at the main laser focal point, so the circle will be about 10 mm in diameter. In practice, the whole affair is so sloppy you get what you get, but at least it’s more easily adjusted.
The M4 bolt clamping the holder to the main laser tube now goes through a Delrin bushing. I drilled out the original 4 mm screw hole to 6 mm to provide room for the bushing:
The bushing has a wide flange to soak up the excess space in the clamp ring:
With all that in place, the dimmer dot is visually about 0.3 mm in diameter:
The crappy image quality comes from excessive digital zoom. The visible dot on the MDF surface is slightly larger than the blown-out white area in the image.
The CO₂ laser hole is offset from the red laser spot by about 0.3 mm in both X and Y. Eyeballometrically, the hole falls within the (dimmed) spot diameter, so this is as good as it gets. I have no idea how durable the alignment will be, but it feels sturdier than it started.
Because the red dot beam is 25° off vertical, every millimeter of vertical misalignment (due to non-flat surfaces, warping, whatever) shifts the red dot position half a millimeter in the XY plane. You can get a beam combiner to collimate the red dot with the main beam axis, but putting more optical elements in the beam path seems like a Bad Idea™ in general.
The OpenSCAD source code as a GitHub Gist:
| // Laser cutter red-dot module fine adjust | |
| // Ed Nisley KE4ZNU 2022-09-22 | |
| Layout = "Show"; // [Build, Show] | |
| /* [Hidden] */ | |
| ThreadThick = 0.25; | |
| ThreadWidth = 0.40; | |
| HoleWindage = 0.2; | |
| Protrusion = 0.1; // make holes end cleanly | |
| inch = 25.4; | |
| ID = 0; | |
| OD = 1; | |
| LENGTH = 2; | |
| function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit); | |
| //———————- | |
| // Dimensions | |
| PointerOD = 8.0 + 0.2; // plus loose turning fit | |
| Aperture = 5.0; // clear space for lens | |
| SkewAngle = 2.5; | |
| MountRing = [10.0,16.0,8.0]; // OEM laser module holder | |
| GripRim = [Aperture,MountRing[OD] + 2*1.5,3.0]; // finger grip around OD | |
| NumSides = 24; | |
| //———————- | |
| // Useful routines | |
| module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes | |
| Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2); | |
| FixDia = Dia / cos(180/Sides); | |
| cylinder(r=(FixDia + HoleWindage)/2, | |
| h=Height, | |
| $fn=Sides); | |
| } | |
| //———————- | |
| // Holder geometry | |
| module Holder() { | |
| difference() { | |
| union() { | |
| cylinder(d=GripRim[OD],h=GripRim[LENGTH],$fn=NumSides); | |
| PolyCyl(MountRing[ID],MountRing[LENGTH] + GripRim[LENGTH],NumSides); | |
| } | |
| translate([0,0,-Protrusion]) // close enough without skew angle | |
| PolyCyl(Aperture,2*MountRing[LENGTH],NumSides); | |
| translate([0,0,MountRing[LENGTH]/2 + GripRim[LENGTH]]) | |
| rotate([0,SkewAngle,0]) | |
| translate([0,0,-MountRing[LENGTH]/2]) | |
| PolyCyl(PointerOD,2*MountRing[LENGTH],NumSides); | |
| } | |
| } | |
| //———————- | |
| // Build it | |
| if (Layout == "Show") { | |
| Holder(); | |
| } | |
| if (Layout == "Build") { | |
| Holder(); | |
| } |
Yeah, this is enough to knock your bike completely off course:
The black smudge matches a scuff on the right sidewall of the front tire. I think I hit it in that orientation and it pivoted clockwise while lifting the bike and shoving the tire to the left.
Another look from what was likely the right side of the shoulder:
I’ll give it a decent burial out back … and be glad our roles aren’t reversed!
We’re southbound on Rt 376, ticking along at about 15 mph, with fresh string-trimmer debris littering the shoulder:
Did you notice the rock? I didn’t.
The fairing ripples as my front tire hits the left side of the rock:
I have no memory of the next two seconds.
The offset impact turns the front wheel to the left, so the bike steers out from underneath my weight:
Because the bike frame was still aimed straight ahead, the wheel is steering further to the left and putting me even more off-balance. I am somehow trying to lean left far enough to get my weight lined up with the bike:
One second into the event, Mary has no idea what’s going on behind her.
My memory resumes with an image of the yellow midline just beyond my left foot:
Mary heard an odd sound and asks (over the radio) “Are you all right?”
I’m approximately balanced, turning toward the shoulder, and manage to shout “NO!”:
I’m coasting toward the shoulder with my feet off the pedals:
Mary is stopping and I coast past her:
Landing gear out:
Back on the shoulder, lining up with the guide rail:
Dead slow:
Docking adapter deployed:
And stopped:
I sat in that exact position for nearly four minutes.
A slideshow view of the same images so you can watch it unfold:
Doesn’t look like much, does it?
If I could have looked over my shoulder, this is what I would have seen, starting at T = 0 with the rock impact blurring the image:
Surely scared the daylights out of that driver, perhaps confirming all the usual expectations of crazy bicyclist behavior.
Here’s what Mary would have seen over her shoulder, again starting at T = 0 with the fairing bulging from the impact:
Timing is everything.
That Benz is new enough to have automatic emergency braking, as it slowed pretty dramatically while I was busy getting out of the way, but it’s not clear whether AEB knows about small / lightweight targets like pedestrians and bicyclists.
We completed the ride as planned, although I finally realized the front fender bracket had broken a few miles later.
Every adult human male has at least one story beginning “But for that millisecond or inch, I wouldn’t be here.” Now I have one more.
I must not fear. Fear is the mind-killer. Fear is the little-death that brings total obliteration. I will face my fear. I will permit it to pass over me and through me. And when it has gone past I will turn the inner eye to see its path. Where the fear has gone there will be nothing. Only I will remain.
Frank Herbert, Dune
The mudflap on my front fender rides low enough to snag on obstacles and the most recent incident (about which more later) was a doozy, breaking the left strut ferrule and pulling the bracket off its double-sticky foam tape attachment. Fortunately, the repair kit now has plenty of duct tape.
The replacement printed up and installed just like its predecessors:
Having the bracket be the weakest link makes perfect sense to me …
Applying a laser cutter to paper-like materials requires balancing two contradictory imperatives:
This seemed like a good compromise:
The orange 3D printed blocks hold aluminum miniblind blades:
The curved slots hold the blades flush with the upper surface and align their top sides parallel to the laser beam, giving the beam very little blade to chew on near the focus point and allowing plenty of room below the sheet to dissipate cutting fumes.
The gold-ish squares are thin steel sheets covered with Kapton tape, painstakingly filed en masse from small snippets:
The first iteration used precisely laser-cut refrigerator magnet pieces, in the expectation a crappy rubber magnet would provide just enough attraction to let a neodymium magnets hold the paper flat, without risk of blood blisters between fingers and steel:
As expected, contact with the neo magnet completely wiped away the alternating pole magnetism in the rubber sheet, leaving a weakly attractive non-metallic surface. Alas, the rubber had too little attraction through a laminated sheet of paper, so I switched to real steel and risked the blisters.
Most of the blocks are narrow:
The four corners are wider:
They’re symmetric for simplicity, with recesses for the magnets / steel sheets on the top. The through-holes have recesses for M3 SHCS holding them to T-nuts in Makerbeam rails, with a slightly overhanging alignment ledge keeping them perpendicular to the rail.
The magnets come from an array of worn-out Philips Sonicare toothbrush heads:
They’re epoxied inside a two-piece mount, with the lower part laser-machined from 3 mm acrylic to put the two magnets in each assembly flush with the lower surface; the green area gets engraved 1 mm below the surface for the steel backing plate. The 1.5 mm upper frame fits around the plate and protrudes over the ends just enough for a fingernail grip:
The epoxy got a few drops of fuschia dye, because why not:
The garish trimmings came from slicing the meniscus around the lower part of the holder off while the epoxy was still flexy.
The holders must be flat for clearance under the focus pen:
Some experimentation suggests I can raise the pen by maybe 2 mm (with a corresponding increase in the Home Offset distance) , but the switch travel requires nearly all of the protruding brass-colored tip and there’s not much clearance under the nozzle at the trip point.
With all that in hand, it works fairly well:
The lower deck has very little margin for gripping, which is why the four corner blocks must be a bit wider than the others.
The lamInator tends to curl the sheets around their width, so most of the clamping force should be along the upper and lower edges to remove the curl at the ends. This requires turning the whole affair sideways and deploying more magnets, which is possible for the smaller middle and upper decks:
Protruding SHCS heads on the four corners snug up against the edge of the knife-edge bed opening for Good Enough™ angular alignment.
Plain paper (anything non-laminated) seems generally flat enough to require no more than the corner magnets.
It’s definitely better than the honeycomb surface for fume control!
The OpenSCAD source code as a GitHub Gist:
| // Bracket for sheet holder | |
| // Ed Nisley KE4ZNU 2022-09-09 | |
| Layout = "Show"; // [Show, Build, Blade] | |
| /* [Hidden] */ | |
| ThreadThick = 0.25; | |
| ThreadWidth = 0.40; | |
| HoleWindage = 0.2; | |
| Protrusion = 0.1; // make holes end cleanly | |
| ID = 0; | |
| OD = 1; | |
| LENGTH = 2; | |
| module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes | |
| Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2); | |
| FixDia = Dia / cos(180/Sides); | |
| cylinder(r=(FixDia + HoleWindage)/2, | |
| h=Height, | |
| $fn=Sides); | |
| } | |
| // Sizes | |
| Magnet = [10,30,0.5]; // magnetic sheet size | |
| //Magnet = [10,14,0.5]; | |
| MagnetRim = 1.0; | |
| Screw = [3.0,5.5,3.0]; // SHCS OD=head LEN=head | |
| MakerBeam = 10.0; // beam size, screw = half height | |
| BeamRecess = 0.5; // slight overhang for alignment | |
| BladeSlot = 0.15 * 4; // slot with plenty of clearance | |
| BladeSocket = 5.0; // recess to hold miniblind | |
| BladeWidth = 24.6; // miniblind width | |
| BladeM = 1.6; // height of miniblind curve | |
| BladeSides = 12*8; | |
| BladeRadius = (pow(BladeM,2) + pow(BladeWidth,2)/4)/(2*BladeM); | |
| BladeAngle = 2*asin(BladeWidth/(2*BladeRadius)); | |
| echo(BladeRadius = BladeRadius); | |
| echo(BladeAngle = BladeAngle); | |
| Block = [Magnet.x + 2*MagnetRim + ceil(BladeRadius*(1 – cos(BladeAngle)) + 2.0), | |
| Magnet.y + 2*MagnetRim, | |
| BladeRadius*sin(BladeAngle)]; | |
| echo(Block = Block); | |
| // Cutter for spline recess | |
| // approximately correct and good enough | |
| module BladeRing() { | |
| rotate([90,0,0]) | |
| translate([0,0,-BladeSocket]) | |
| linear_extrude(height=2*BladeSocket,convexity=2) | |
| difference() { | |
| circle(r=BladeRadius,$fn=BladeSides); | |
| circle(r=BladeRadius – BladeSlot,$fn=BladeSides); | |
| } | |
| } | |
| // Overall bracket | |
| module Bracket() { | |
| difference() { | |
| translate([0,-Block.y/2,0]) | |
| cube(Block,center=false); | |
| translate([Magnet.x/2 + MagnetRim,0,Block.z – Magnet.z/2 + Protrusion/2]) | |
| cube(Magnet + [0,0,Protrusion],center=true); | |
| for (j=[-1,1]) | |
| translate([0,j*Block.y/2,MakerBeam/2 – Protrusion/2]) | |
| cube([3*Block.x,2*BeamRecess,MakerBeam + Protrusion],center=true); | |
| for (j=[-1,1]) | |
| translate([Magnet.x + 2*MagnetRim + BladeRadius,j*Block.y/2,Block.z]) | |
| BladeRing(); | |
| for (j=[-1,1]) | |
| translate([Block.x – 2.0 – BladeSlot,j*Block.y/2,5*ThreadThick/2 – Protrusion/2]) | |
| cube([2*BladeSlot,2*BladeSocket,5*ThreadThick + Protrusion],center=true); | |
| translate([MakerBeam/2,Block.y,MakerBeam/2]) | |
| rotate([90,0,0]) | |
| PolyCyl(Screw[ID],2*Block.y,6); | |
| for (j=[-1,1]) | |
| translate([MakerBeam/2,j*(Block.y/2 – Screw[LENGTH] – 1.0),MakerBeam/2]) | |
| rotate([-j*90,0,0]) | |
| PolyCyl(Screw[OD] + HoleWindage,2*Block.y,6); | |
| } | |
| } | |
| //———- | |
| // Build it | |
| if (Layout == "Blade") | |
| BladeRing(); | |
| if (Layout == "Show") | |
| Bracket(); | |
| if (Layout == "Build") | |
| Bracket(); |
On occasion I will do something practical:
It’s not that we needed a rack for those cans, but it did get a laugh from Mary and that’s what counts.
The magic URL encoding all the parameters to generate a rack, using a recent addition to the wonderful boxes.py collection:
https://www.festi.info/boxes.py/CanStorage?FingerJoint_angle=90.0&FingerJoint_style=rectangular&FingerJoint_surroundingspaces=0.0&FingerJoint_edge_width=1.0&FingerJoint_extra_length=0.0&FingerJoint_finger=2.0&FingerJoint_play=0.0&FingerJoint_space=2.0&FingerJoint_width=1.0&Stackable_angle=60&Stackable_height=2.0&Stackable_holedistance=1.0&Stackable_width=4.0&fillHoles_bar_length=50&fillHoles_fill_pattern=no+fill&fillHoles_hole_max_radius=15&fillHoles_hole_min_radius=5&fillHoles_hole_style=hexagon&fillHoles_max_random=1000&fillHoles_space_between_holes=10.0&fillHoles_space_to_border=15.0&top_edge=%C5%A0&bottom_edge=%C5%A1&canDiameter=80&canHight=115&canNum=6&chuteAngle=5.0&thickness=3.2&format=svg&tabs=0&debug=0&labels=0&labels=1&reference=0&inner_corners=loop&burn=0.04&render=0
In order from left to right, the three successive racks represent:
The Burn Correction Factor encapsulates many physical effects and, much like 3D printing’s Extrusion Multiplier, must be determined empirically.
The axis scale error, however, took me by surprise.The X axis travels on the order of 0.2 mm more along 250 mm, about 0.08%, than the Y axis, even after my tedious calibration. I must do that calibration again, because, as Miss Clavel observed in a different context, Something Is Not Right.
And, yes, that tiny difference is enough to misalign the last few fingers with their holes, to the extent of requiring somewhat more than Gentle Persuasion with a plastic mallet.
The Smell of Molten Projects in the Morning 