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.

Author: Ed

Hotel California: Vole Edition

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:

Vole Box – large

That’s a rat-size trap.

A smaller box has room for two mouse-size traps (one hidden on the left):

Vole Box – small

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.

2025-01-28
Walking to Work: Goose Gaggle

As the poster says, “Until you spread your wings, you’ll have no idea how far you can walk”:

Goose Tracks – Vassar Sunset Lake – A

My feet get chilly just looking:

Goose Tracks – Vassar Sunset Lake – B

We think the flock has a Rules Compliance Officer who gave one miscreant goose an all-around inspection:

Goose Tracks – circling

Just another day at the office …

The WordPress AI generated an excerpt for this post:

The poster emphasizes potential discovery through exploration, while the goose flock exhibits curiosity, hinting at humorous governance among them at Vassar Sunset Lake.

I had no idea “governance” was a goose thing.

2025-01-27
Clothes Dryer Inlet Filter Holder
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:

Dryer Inlet Vent – filter retainer

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:

Dryer Inlet Vent Filter Retainer – solid model

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 …
2025-01-24
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
HLP-200B Laser Power Meter: Mirror Losses

With the manual laser pulse button in place, I measured the beam power at the entry and exit planes of Mirror 1 and Mirror 2, with the differences indicating something about the reflectivity (or lack thereof) of the molybdenum mirrors. Given that the losses are on the order of a few percent, tops, I expected this to be below the repeatability of the measurements.

The Mirror 1 entry point is basically the same as the laser tube exit:

HLP-200B – Laser tube exit

The Mirror 1 exit plane is perpendicular to that, just behind the mirror, but there is no way I can get a picture of the arrangement. Suffice it to say I do not want to ever put any body parts that close to an operating laser tube again.

The HLP-200B meter turned out to be exactly the right length to stand on its own in front of Mirror 2, although I needed a few test shots to figure out the lateral positioning:

HLP-200B Mirror 2 entry check

The Mirror 2 exit measurements were hand-held, with the meter braced against the mirror mount brackets on the gantry:

HLP-200B Mirror 2 exit

Without further ado, the results:

M1 Entry M1 Exit M2 Entry M2 Exit
35.5 31.2 30.3 32.9
28.3 30.6 29.1 32.6
31.8 22.8 27.8 28.9
30.3 29.0 29.4 28.5
26.9 28.4 28.7 27.0
31.1 31.7 28.6 26.9
30.7 29.0 29.0 29.5
2.99 3.27 0.84 2.67

The bold line gives the average of the six measurements at each position, with the sample standard deviation below that.

As expected, the pulse-to-pulse variations swamp any actual differences between the entry and exit power levels; Mirror 2 does not have a net power gain. A 2% loss in the mirror is 0.6 W at 30 W, obviously far too small for the HLP-200B meter to resolve.

I must once again set up the photocell to measure the stray IR scattered around the beam, measure the actual tube current, then see if the two vary as much as the HLP-200B says the beam power does.

2025-01-21
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

M1 Entry	M1 Exit	M2 Entry	M2 Exit
35.5	31.2	30.3	32.9
28.3	30.6	29.1	32.6
31.8	22.8	27.8	28.9
30.3	29.0	29.4	28.5
26.9	28.4	28.7	27.0
31.1	31.7	28.6	26.9

30.7	29.0	29.0	29.5
2.99	3.27	0.84	2.67

Author: Ed

Hotel California: Vole Edition

Walking to Work: Goose Gaggle

Clothes Dryer Inlet Filter Holder

CD/DVD Data Destruction: Engraving

HQ Sixteen: Heisenbug vs. Schematic

HLP-200B Laser Power Meter: Mirror Losses

Whole House Filter Disassembly