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: Science

If you measure something often enough, it becomes science

Subaru Forester Gas Tank Capacity, Experimental Measurement Thereof
According to the manual, which I have hitherto had no reason to doubt, our non-turbo 2015 Subaru Forester has a 15.9 gallon fuel tank:

Subaru Forester – Fuel Capacity Chart

One screen shown on the dashboard’s Multi-Function Display gives the current mileage and estimated range:

Forester – MPG Range

Dividing those two numbers gives you 13.97 gallons, the current fuel level. As you’d expect, should the average miles per gallon change, the range will change accordingly.

The trip odometer says we have driven 72.8 miles since I filled the tank. Dividing that by the average mpg gives 2.3 gallons, so the tank could possibly hold 16.2 gallons, which, given all the averages involved, is reasonably close to the 15.9 gallons shown in the manual.

Being that type of guy, I have a spreadsheet tallying each fillup since the car was new:
- 8.1 gal average
- 7.5 gal median
- 13.9 gal maximum
Long ago, my father taught me to fill the tank when the needle got halfway down and I’ve been doing so ever since. As a result, we have only rarely seen the Low Fuel Warning Light:

Subaru Forester – Low Fuel Warning Light info

A concatenation of unavoidable events put us southbound on I-87 when that light went on. Given the estimated range of 70-ish miles, I planned to refuel at the New Baltimore Service Area, about a dozen miles ahead.

The engine shut down and all the dashboard warning lights lit up with the Service Area Ahead sign in view:

Out of Gas – Service Area Ahead

All the “facilities” are blank because they’re rebuilding the whole place, with the gas station remaining open.

So I slapped the shifter into neutral and we drifted slowly along the shoulder, under the bridge visible ahead, and eventually came to a halt at the beginning of the exit lane.

There was only one thing to do:

Out of Gas – Walking On

Some storytelling later:

Out of Gas – Walking Back

Just because I could:

Refueling – GPS Track

For what are, I trust, understandable reasons, I started the tracker after I began hiking and forgot to turn it off before driving away.

After figuring out the devilishly complex spring-loaded anti-spill spout on the gas can, we drove 1500 feet to the Service Area:

Out of Gas – Service Station

As usual, I filled the tank until the nozzle automatically shut off, for a total of 13.554 gallons in two transactions:

Pump Receipts

Now, it is possible the Forester fuel system has another 2.3 gallons tucked away somewhere, but if that reserve doesn’t make the wheels go around, it’s not doing me the least bit of good.

The fact that I’ve occasionally added just short of 14 gallons suggests the estimated remaining capacity depends strongly on the average mileage up to that point and I have come very very close to running out of gas on several occasions.

As far as I can tell, the usable fuel capacity is a scant 14 gallons and the Low Fuel Light goes on with, at most, a dozen more miles in the tank.

This is the second time in more than half a century of driving I’ve run out of gas.

My father was right and I shall henceforth mend my wayward behavior.
2023-04-17
Laser Air Assist Pump Filter: Ewww!

Nine months ago I packed cheesecloth around the laser’s air assist pump inlet to filter the smog:

OMTech 60 W Laser Air Assist – cheesecloth filter installed

Which worked better than I expected.

I think the track on the right side of the lower / outer filter faced the interior of the cabinet and collected some incoming smog:

Laser cutter assist air filter – 9 months – outer

The wad packed around the inlet fitting accumulated even more, due to the concentrated air flow through the round opening:

Laser cutter assist air filter – 9 months – inner

Thus we can confirm putting the air pump inside the cutting chamber is not a particularly good idea:

OMTech 60W laser – Z motor – air pump

My initial notion of drilling a hole through the bottom of the cabinet so the pump can breathe relatively clean basement air takes on new urgency …

2023-04-06
LED Shoplight Conversion: First Failure

Having started replacing the fluorescent shop lights with LED tubes back in 2016, this was only a matter of time:

Shop Light – failing LEDs

The next morning the dead section lit up again, albeit with a dim ring at its right end. I think one LED in that string failed open and darkened the whole string, then failed short under the voltage stress, and is now quietly simmering in there with slightly higher than usual current.

The lights over the workbench weren’t in the first wave of conversions, so they may be only four years old.

For sure, they have yet to approach their 50000 hour lifetime …

2023-03-24
Medium Ricotta Lid Box: QR Code vs. Chipboard
Another box from the festi.info box configurator to collect more lids in a kitchen drawer:

Medium Ricotta Lids box

This was really a thinly veiled excuse for a deeper look at the QR code generator encoding the myriad parameters required to create the box and see what happens when you try to burn such a complex thing into chipboard.

Spoiler: chipboard has very low contrast and really does not work well with high-density QR codes.

Although the festi.info box generator can produce QR codes, I used qrencode (available in your Linux distro) on the command line to generate QR code image files with specific settings:
```
qrencode --level=M --size=6 --dpi=254 --output='Ricotta Lids 2 lb - chipboard.png' 'http://festi.info/boxes.py/ABox?FingerJoint_angle=90.0&FingerJoint_style=rectangular&FingerJoint_surroundingspaces=2.0&FingerJoint_bottom_lip=0.0&FingerJoint_edge_width=2.0&FingerJoint_extra_length=0.0&FingerJoint_finger=2.0&FingerJoint_play=0.0&FingerJoint_space=3.0&FingerJoint_width=1.0&x=200.0&y=120.0&h=60.0&outside=0&bottom_edge=h&thickness=1.4&format=lbrn2&tabs=0.0&qr_code=0&debug=0&labels=0&reference=0&inner_corners=corner&burn=0.04&language=en&render=0'
```
The key parameters:
- --level → error correction level
- --size → size of the smallest square (“module”) in pixels
- --dpi → DPI of the output image file
The default file type is PNG. The unusual 254 DPI makes each pixel exactly 0.1 mm wide and a peculiar 169.33 DPI = 0.15 mm came in handy for the first pattern.

The final parameter is the character string to encode, which you should definitely quote to prevent the shell from wrecking things while trying to help you.

A pattern with 4×4 pixel modules didn’t scan at all:

Chipboard QR code – 15pct 0.15mm 4×4 – overview

A closer look shows the modules have ragged edges due to laser timing variations during the engraving scans and gaps between successive scans because the spot size is less than the 0.15 mm scan interval:

Chipboard QR code – 15pct 0.15mm 4×4 – detail

Increasing the module to 6×6 pixels at a 0.1 mm scan interval :

Chipboard QR code – 15pct 0.10mm 6×6 – overview

A closer look shows the larger module reduces the relative size of the timing errors, while the decreased line spacing tidies up the blocks:

Chipboard QR code – 15pct 0.10mm 6×6 – detail

Reducing the power from 15% to 10% reduced the contrast to the point of illegibility:

Chipboard QR code – 10pct 0.10mm 6×6 – overview

A closer look shows the engraving barely punches through the surface and has somewhat more ragged edges due to the tube’s pulsating startu p current at very low power:

Chipboard QR code – 10pct 0.10mm 6×6 – detail

I also tried 5×5 modules with similar results.

The laser spot size sets the engraving scan interval, which then determines the DPI value for the QR code image. With all that matched up, you can send the images directly to the laser in Passthrough mode, without having LightBurn resample the pixels and change the module’s shape.

Looked at from a different angle: given the laser spot size and the module size, the QR code image size is not under your control.

From another angle: given a QR code image size in, say, millimeters, and the engraving scan interval, the module size is not under your control.

All this is moot if you print QR codes on a high-resolution / high-contrast printer. It’s just the gritty nature of laser cuttery that limits what you can accomplish.

And, of course, using a material less awful than chipboard will definitely improve the results.

If you want a similar box of your own, here ya go:

Medium Ricotta Lids – chipboard QR code – default

The URL is too ugly to print, but you can copy it from this link.
2023-03-16
Gas Price Signage: FAIL

The big price displays at the Mobil station on the corner have always behaved oddly, but these replacements began failing within a week of their installation:

Mobil price sign – north face

That doesn’t look too bad, until you notice the number of dead LEDs in both red displays.

The south face is in worse shape:

Mobil price sign – south face

The green LEDs seem to be failing less rapidly than the reds, but I don’t hold out much hope for them.

The previous display had seven-segment digits made of smooth bars, rather than discrete LEDs. This one appeared after the segments failed at what must have been more than full brightness; the red LEDs were distracting by day and blinding by night.

Maybe they got the LEDs from the same folks selling traffic signals to NYS DOT? The signals around here continue to fail the same way, so I suppose DOT doesn’t replace them until ~~somebody~~ enough people complain.

2023-03-10
Please Close The Gate Signs: MDF Weathering

With the new signs in place, the old ones paused briefly for a photo op on their way to the trash:

Please Close The Gate – weathered MDF

That’s eight months of weathering on MDF covered with indoor urethane sealant and it’s not as awful as I expected: the MDF didn’t actually disintegrate, it just collected some mold / mildew / crud.

A closer look:

Please Close The Gate – weathered MDF – detail

The black paint survived surprisingly well.

I hadn’t paid ~~much~~ any attention to the edges, so they got covered with random amounts of black paint and urethane. It seems that’s where the disintegration starts:

Please Close The Gate – weathered MDF – side view

MDF definitely isn’t the right material for an outdoor sign and I knew that going in, but it’s cheap and readily available, which makes up for a lot.

For comparison, they looked nice right after installation:

Please Close The Gate – fresh painted

Ya learn something new every year around here!

2023-03-09
Tree vs. Guide Rail: Sheared Bolt

Spotted on a walk along the Mighty Wappingers Creek after a storm with plenty of gusty winds:

Tree-smashed guide rail

The tangle of branches and logs came from a tree that fell across the road from the far right side and put that crease into the guide rail. The vertical stump seems unrelated to that incident.

A bit of rummaging at the base of one post produced a victim:

Tree-smashed guide rail – sheared bolt – side

The impact produced enough force to turn the rail brackets into guillotine metal shears against the posts:

Tree-smashed guide rail – sheared bolt – end

It’s not a clean shear cut, which isn’t surprising under the circumstances.

An ordinary ½-13 Grade 8 bolt has a 17 k pound proof load: popping that bolt required a mighty oomf.

Memo to Self: stay indoors during windy storms!

2023-02-24