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.

Category: Home Ec

Things around the home & hearth

CD/DVD Data Destruction: Engraving

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:

CD Engraving – fixture

The overall effect is, in most lighting, subtle:

CD Engraving – samples 2

The pair on the right with inverted engraving areas are bolder:

CD Engraving – samples 1

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):

CD Engraving – vary interval

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:

CD Engraving – vary power

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):

CD Engraving – interval passes

A closer look at the border:

CD Engraving – low power irregularity

The reason behind the granular effect at 10% power is more obvious with higher magnification:

CD Engraving – interval passes – detail

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.

2025-01-23
HQ Sixteen: Heisenbug vs. Schematic
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:

HQ Sixteen – Power PCB – schematic 2025-01-14

As before:
- Do not assume any connections or components are correct or correctly drawn.
- !!CAUTION!! The motor supply is direct-from-the-AC-line non-isolated +160 VDC.
- !!CAUTION!! The 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.
2025-01-22
Whole House Filter Disassembly

The sediment and carbon filter cartridges in our house call for annual replacement and I wondered what was inside the big cartridge.

Much to my surprise, the white plastic cap unscrews easily after grabbing the filter in the bench vise and applying a strap wrench:

Whole house carbon filter – endcap

Water enters around the perimeter of the cap, flows through the media in the cylindrical cartridge, and emerges near the center at the other end. The filter is upside-down in the vise: the cap is on the bottom of the cartridge when it’s installed in the filter housing.

The brown stuff looks a lot like sand, but is probably KDF-85 media acting as a prefilter for the carbon:

Whole house carbon filter – prefilter

The white fiber pad separates the KDF-85 from the carbon granules filling the rest of the filter:

Whole house carbon filter – carbon

Atypically, I couldn’t think of anything to do with the empty cartridge, so I screwed the lid back on and lowered the whole mess into the trash can.

Now I know what’s inside!

2025-01-20
Samsung Refrigerator Condenser Coil Cleaning
The kitchen came with matched Samsung appliances dating back to 2018 and, on a frigid winter day, we piled the contents of the freezer on the porch and gave it a deep cleaning. While the empty freezer was cooling down from its adventure, I wondered:
- Where were the condenser coils were located?
- Did they need cleaning?
- How does one do that?
The manual is strangely silent about even the existence of the coils, so evidently cleaning them wasn’t of any importance to Samsung.

Rolling the refrigerator away from the wall just enough to get the phone camera down there suggests they exist and are in need of some attention:

Samsung refrigerator coils – first sight

Rolling the refrigerator out until the door handles met the countertop across the way let me climb over the counter and worm myself into the refrigerator-sized hole behind it, bringing along a screwdriver, the vacuum cleaner snout, and a few brushes.

Removing five screws released the back cover:

Samsung refrigerator coils – cover off

Looking into the intake end of those coils (on the right):

Samsung refrigerator coils – first intake view

So, yeah, I’m about to give them their first cleaning ever.

Five minutes of brushing fuzz, mostly into the vacuum, cleared a good bit of the exterior, but the interior needs more attention:

Samsung refrigerator coils – partial clean

Ten minutes later:

Samsung refrigerator coils – victory

Another five minutes:

Samsung refrigerator coils – intake cleaned

Making the coils cleanable and putting them where they could be cleaned were obviously not bullet-item goals for Samsung’s designers.

Although the coils are not perfectly clean, I don’t know how to get them any cleaner, despite knowing even a thin layer of fuzz kills the refrigerator’s much-touted energy efficiency. Perhaps blowing them off with compressed air, then cleaning a thin layer of dust off the entire kitchen, would help.

I think the refrigerator will be happier, at least for a while.
2025-01-16
Quick-n-Easy Window Shade End Cap
While tracking down an air leak in a living room window, I noticed one of the cellular blinds was missing an end cap, so I scanned a pair of surviving caps:

Living Room shade end caps – level adjust

Blow out the contrast, save as a JPG.

Import into LightBurn:
- Trace the outlines into paths
- Use LightBurn’s shape optimization tool to dramatically reduce the number of nodes & smooth the outlines
- Overlay & align the shapes
- Export as an SVG file
Import into Inkscape:
- Put the paths on named layers
- Center around an alignment mark
- Save as an Inkscape SVG
Living Room shade end caps – Inkscape alignment

It is slightly tilted, but that doesn’t matter. You could devote more time to smoothing / reverse-engineering the shapes, but that doesn’t make much difference, either.

Inkscape exports the SVG coordinates with respect to the overall page origin in the lower left corner, so when OpenSCAD imports the SVG the paths end up far away from the origin. The trick is to put a 2 mm diameter circle at a known location, center the paths around it, then have OpenSCAD use the circle’s location to recenter the paths.

Because Inkscape uses the lower left corner of each shape as its origin, you must put the circle at (99,99) to have its center at (100,100). That is one of the many reasons you (well, I) can’t use Inkscape as a CAD program.

Import into OpenSCAD, recenter, and extrude the shapes:
```
CapCenter = [100,100];

PlateThick = 1.8;       // thickness of visible end cap

HolderTall = 10.0 + PlateThick;

union() {
  linear_extrude(height=PlateThick)
      translate(-CapCenter)
            import("Living Room shade end caps - Inkscape.svg",layer="Exterior");
  linear_extrude(height=HolderTall)
      translate(-CapCenter)
            import("Living Room shade end caps - Inkscape.svg",layer="Retainer");
}
```
Which produces a solid model:

Living Room shade end caps – solid model

Save the model as 3mf, import into PrusaSlicer, and slice:

Living Room shade end caps – PrusaSlicer preview

Making the retainer shape a little wider would be a good idea to get better infill, but it’s a slip fit into the blind (surely why it fell out long ago) and need not withstand any stress.

Print as usual:

Living Room shade end cap – on platform

And then It Just Works™:

Living Room shade end cap – installed

It’s sitting atop a bookcase while I finish tinkering with its window.

All that seems like a lot of fiddling around, but it uses each program to its best advantage and it’s surprisingly easy after the first few models.
2025-01-09
Handi-Quilter HQ Sixteen: Preliminary Power PCB Schematic

Because I must eventually diagnose and fix the HQ Sixteen’s Motor Stall Heisenbug, I printed out several views of the power supply PCB on glossy photo paper for best visibility.

The component side:

Power PCB – components

The solder side:

Power PCB – solder

The X-ray view:

Power PCB – overlaid

Considerable pondering and sketching produced an annotated view of the solder side:

HQ Sixteen – Power PCB – solder side – component labels – reduced

Here’s a tentative schematic drawn on the fly while extracting it from the PCB traces:

HQ Sixteen – Power PCB – rough schematic

!!CAUTION!! I have not verified the schematic against the actual hardware / PCB / components, as the Heisenbug has not reoccurred and I had no occasion to take the machine apart for checking. Do not assume any connections or components are correctly drawn.

Before I redraw the schematic in a more useful format, I must verify several nodes, because not everything in there makes sense.

In particular, the elaborate resistor string in the middle of the page seems to establish reference voltages for everything else, from the motor power supply turn-on delay to the RUN signal starting the motor.

The optoisolators definitely get the RUN command signal from the controller and feed the STALL motor status back to it. That’s assuming I understand enough to pin those labels on those connections.

!!CAUTION!! Read my caveats about the direct-from-the-AC-line non-isolated +160 VDC motor supply before connecting your instruments. The GND traces are not isolated from the AC line and are not at the normal “0 V” AC neutral potential.

But if this mess gets you further along with whatever you were doing, let me know how it all worked out for you.

2025-01-08
Christmas Non-Wrapped Box
Mostly to find out if I could do it:

Christmas Wrap custom box

The process:
- Fetch a printable wrapping paper pattern, ignore the watermark
- Resize / crop to fit a Letter page, print two copies on glossy photo paper
- Generate a suitable multi-sheet paper box in SVG format
- Import into LightBurn
- Rearrange / splice the parts to put the main box on one Letter size sheet and the end caps on another
- Fire The Laser to score (blue lines) and cut (red lines) the paper
- Assemble using a glue stick
- Fill with Christmasy stuff (your choice may vary)
- Tuck the flap, there’s no need to wrap!
The rearranged main box just barely fits across a Letter page:

Non-Wrapped Christmas Box – main piece – LightBurn layout

You can make many more end caps than you need:

Non-Wrapped Christmas Box – endcaps – LightBurn layout

Obviously, this makes no sense whatsoever in terms of box making, but the recipient smiled and that’s what I wanted.
2025-01-02