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.
Things around the home & hearth
Given the cracking caused by vector patterns on CDs and DVDs, seeing stress cracks open up on large-area engravings came as no surprise:
They start smaller in the more closely engraved areas:
But eventually spread over the entire surface:
They’re not always straight:
And aren’t aligned with the engraving path:
My threat model says those discs are definitely unreadable …
The ↓ (“down”) button on one of our lift chairs stopped working, although the ↑ (“up”) button worked fine and, as you’d expect, verifying this problem left the chair in a rather awkward position.
The usual power cycle and unplugging / replugging the control had no effect.
This control is the one I couldn’t pry apart to dim its LEDs, so I tried various combinations of pins until this scribble emerged:
I have no idea of the correct pin numbering, but the scribble looks into the connector pins with the keyway on top:
The more intricate control for the other Pride lift chair has only four pins in its connector, so I couldn’t just swap them to see what happened.
The polarities are for the continuity / resistance test probes.
The takeaway: The two buttons did similar things to two different connector pins, so the control seemed to be working correctly and the fault lies elsewhere.
The control sports a USB jack for powering / charging your favorite device and I’m reasonably sure the control has a microcontroller tucked in there for good reason, implying the circuitry is surely more complex than maybe a rectifier bridge and some resistors.
So I shoved the chair into the middle of the room, deployed some test equipment, reconnected the control, plugged the chair power supply into the outlet strip, and … of course both buttons worked perfectly.
Soooo the chair is back in place and we’ll see what happens next.
Speaking of Heisenbugs, the HQ Sixteen continues to work fine, too.
The HQ Sixteen consumes thread at a prodigious rate, so it’s set up for large thread cones. Mary sometimes uses ordinary thread spools (leftovers from sewing projects) for short practice sessions and wanted an adapter to hold the little things in place:
Those of long memory should recall previous adapters for both sizes and their notes about how thread should peel off spools & cones. I considered an adapter with a horizontal spool axis, but contemporary machines apparently don’t bother with such niceties. We may need a right-angle adapter to let the thread pull off from the side, but we’ll start simple and fix it if needs be.
Update: It needed fixing.
The solid model looks about like you’d expect:
The small crosswise hole in the hub gets an M3 setscrew pushing a rubber pellet slightly into the central bore for a friction fit. The OpenSCAD code can distribute any number of such holes, but one seemed entirely adequate.
The code shrinkwraps a hull() around two cylinders to create the tapered sides, thus giving the thread less surface to drag across. I have PrusaSlicer set to produce scarf joints around the perimeter and the edges came out surprisingly smooth, with only one rough spot requiring deft Xacto knife work. It’s made from white PETG for a smoother finish than PETG-CF.
The OpenSCAD code consists mostly of constants defining the various physical measurements and a few lines assembling the model:
// HQ Sixteen - thread spool adapter
// Ed Nisley - KE4ZNU
// 2025-01-21
include <BOSL2/std.scad>
/* [Hidden] */
PinOD = 0.25*INCH;
RingOD = 50.0; // outer perimeter of thread ring
RingEdge = 3.0; // height of ring edge & tapers
RingAngle = 45; // upper & lower tapers wrt vertical
RingOAH = 3*RingEdge;
ScrewOD = 2.5; // tap for setscrew compressing rubberdraulic piston
NumScrews = 1;
HubOD = 25.0;
HubThick = 2*ScrewOD;
HubSides = 12;
ScrewCL = RingOAH + HubThick/2;
AdapterOAH = HubThick + RingOAH;
Protrusion = 0.1;
NumSides = 12*3*4; // smooth outer perimeter
//----------
// Build it
difference() {
union() {
hull() {
linear_extrude(RingOAH)
circle(r=RingOD/2 - RingEdge*tan(RingAngle),$fn=NumSides);
up(RingEdge)
linear_extrude(RingEdge)
circle(d=RingOD,$fn=NumSides);
}
linear_extrude(HubThick + RingOAH)
rotate(180/HubSides)
circle(d=HubOD,$fn=HubSides);
}
down(Protrusion)
rotate(180/HubSides)
cylinder(d=PinOD,h=2*AdapterOAH,$fn=HubSides);
for (i=[0:NumScrews-1]) {
a = i*360/NumScrews;
zrot(a)
up(ScrewCL)
yrot(90)
zrot(180/6)
cylinder(d=ScrewOD,h=HubOD,$fn=6);
}
}
Putting the adapter in the light box revealed the same problem as photographing white dogs in snowstorms:
There was no contrast to be enhanced anywhere, although the rubber pellet definitely stands out.
Although we had considerable success trapping voles during the last half of the 2024 gardening season, Mary found a description of what might be a better technique: a box with small entrance holes taking advantage of rodent thigmotaxis: their tendency to follow walls. The writeup shows nicely made wood boxes, but I no longer have machinery capable of cutting arbitrarily large wood slabs into pieces.
I do, however, have a vast pile of cardboard boxes:
That’s a rat-size trap.
A smaller box has room for two mouse-size traps (one hidden on the left):
The general idea: plunk the box in a garden plot, arm the trap(s), close the lid, and eventually a vole will venture inside, whereupon wall-following leads to disaster. Apparently bait is optional, as wall-following inevitably takes them over the trap pedal. I won’t begrudge them a walnut or two, should bait become necessary.
Cardboard is obviously the wrong material for a box in an outdoor garden, but I figure they’ll survive long enough to show feasibility and I can deploy a lot of small boxes before having to conjure something more durable.
Yes, those are laser-cut rounded-rectangle holes: 30 mm and 40 mm, assuming voles care about such things.
Edit: More on voles.
It has always seemed like a Bad Idea™ to run indoor air through the clothes dryer and dump it overboard, particularly during days when the indoor air has been painstakingly (perhaps expensively) heated or cooled. The dryer now lives in a separate room with two doors, so we can close it off from the rest of the house and let it inhale outdoor air through the screen on the storm door.
Except in winter, when a glass pane covers the screen. Propping the door open just a bit is unattractive, because an open door seems like an invitation to any field mouse looking to upgrade its domicile.
Given that the dryer exhausts through a length of 4 inch flexible duct, I figured a similar vent, facing inward, mounted on the storm door would admit enough air to keep it happy. Keeping insects and adroit mice out requires a screen:
After taking that picture, I rammed four threaded brass inserts into the holes, thereby eliminating the need for a handful of washers and nuts, some of which were absolutely certain to disappear through gaps in the deck.
The two blue-gray rings are PETG-CF:
The small split makes the inner retainer just springy enough to fit over the two small tabs normally locking a dryer hose in place.
The OpenSCAD code gloms a few shapes together:
include <BOSL2/std.scad>
/* [Hidden] */
VentID = 102.0; // diameter at base of vent opening
VentOD = 107.5;
OpenAngle = 3;
LipWidth = 3.0; // lip around vent opening
LipThick = 7.5;
StrutWidth = 2.5; // wide enough to hold filter
StrutThick = 3.0; // tall enough to be rigid
NumStruts = 3;
Protrusion = 0.1;
NumSides = 360/6;
$fn=NumSides;
//----------
// Build it
union() {
linear_extrude(LipThick)
ring(NumSides,d1=VentID - 2*LipWidth,d2=VentID,angle=[OpenAngle/2,360-OpenAngle/2],spin=270);
linear_extrude(StrutThick) {
circle(r=StrutWidth);
for (i=[0:(NumStruts-1)]) {
a = 90 + i*360/NumStruts;
zrot(a)
right(VentID/4)
square([VentID/2 - LipWidth/2,StrutWidth],center=true);
}
}
linear_extrude(LipThick) // outside trim ring
ring(NumSides,d1=VentOD,d2=VentOD+2*LipWidth);
}
The overall union() keeps PrusaSlicer from identifying the thing as a multi-material model. Apparently, it still looks enough like a logo to qualify for special treatment, but I fought it to a standstill.
Installation awaits an above-freezing day …
A LightBurn video suggested large scan line intervals for decorative effects, so I adapted the SCP warning labels to fit 4 inch CD/DVD discs, set up the fixture, and Fired The Laser:
The overall effect is, in most lighting, subtle:
The pair on the right with inverted engraving areas are bolder:
From a distance these two look similar, but a line interval of 0.50 mm (on the left) produces a distinct lined effect compared to the overall frosty look for 0.25 mm (open in a new tab & zoom in):
The left and right edges of the disc warp upward as the surface melts and cools, pulling the disc into a potato chip shape. Doing large areas with 0.5 mm spacing produces less warp than 0.25 mm.
The laser barely fires at 10% power (on the right) and produces a line with a distinct granular look compared the smoother result at 20% (on the left), both at 0.50 mm interval to show the lines:
A 2 mm border at 0.25 mm interval (on the right, with a DVD) appears lighter than the central area at 0.50 mm (the CD on the left does not have the border):
A closer look at the border:
The reason behind the granular effect at 10% power is more obvious with higher magnification:
The spots off to the right are surface imperfections and dirt, not random laser tube firing.
The border and the central area happen on two different passes, so it’s comforting to see how closely the scan lines match.
I glued pairs of discs together with E6000 adhesive to discover whether it’s less awful than cutting and aligning adhesive sheets. Yup, much better, but white adhesive requires better path control to keep it out of the transparent ring around the hub and better quantity control to prevent blobs from squooshing out around the perimeter. Using clear adhesive would help, as would a fresh tube without a plug of cured gunk blocking the nozzle.
Once again, I have Too Many Coasters.
After running reliably for a few weeks, the HQ Sixteen Heisenbug returned, displaying a Motor Stall error on the first attempt to run the motor. This gave me the opportunity to extract the PCB, compare it with the first rough schematic, then correct a few resistor values and connections.
Redrewing (most of) it in somewhat canonical form:
As before:
GND traces are not isolated from the AC line and are not at the normal “0 V” AC neutral potential.When the machine operates normally, the relay pulls in with a distinct click slightly after the power switch closed. With the Heisenbug in full effect, the relay does not click, suggesting a fault in its driver circuitry.
With the motor pod resting on a box beside the machine, I gingerly measured the voltage at various points on the top of the PCB. As far as I could tell, the entire +15 VDC power supply was dead: no voltage at either the input or output terminal of the LM7815 regulator!
NOTE: The obvious screws along the top edge of the PCB are not connected to the power PCB circuit GND. Instead, they’re part of the controller’s power circuitry from the isolated power supply produced by rectifier bridge B3 and passed through J1 in the upper left corner of the PCB. Instead, the left lead on R1 (the 5W sandbox resistor) is a convenient GND terminal.
So I hauled the little DSO150 battery-powered oscilloscope and a handful of clip leads up from the Basement Laboratory, got everything arranged, turned on the power, and the machine worked perfectly again.
That’s why it’s called a Heisenbug: look at it and it vanishes.
Given a faint indication of power supply problems, I verified all four diodes in Bridge Rectifier B21 are OK and the Skynet transformer windings were solid. I resoldered all the PCB connections from the transformer to U2, the LM7815 regulator, plus the green jumper wires.
The machine is now back together, it continues to work, and all my test equipment is back in the basement.
If it happens again, I’ll mount a cheerful LED on the pod to show the supply is working.
The Smell of Molten Projects in the Morning 
