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
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.
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:
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.
The improved Holly Mirror Coaster looks pretty good:
Holly Coaster – overview
Until you realize some of those specks aren’t surface dust and take a closer look:
Holly Coaster – mirror speckles 1
The surface scratches are doubled by their reflection in the bottom mirror. The little dots that aren’t doubled reveal marks in the mirror surface itself.
In this case, they cause defects in the mirror coating allowing alcohol from the fat-tip permanent markers coloring the engraved areas to hit the acrylic. The starbursts come from stress cracks around the punctures.
Peering even closer shows similar cracks along the edges of the colored areas:
Holly Coaster – mirror speckles tight detail
Not much to do about the random speckles, but it’s obvious I must up my coloring game.
Which would be significantly easier if rattlecan spray paint sprayed at winter temperatures …
It’s now oriented with the back side of the lens toward the unfocused beam going into the laser head.
The front surface remains undamaged after two pulses at 500 ms 50% power:
Laser vs sunglasses – beam rear – front overview
The red disk in the middle of both wounds is new this time.
As seen from the rear, the first pulse shattered the rear glass layer:
Laser vs sunglasses – beam rear – A
The image is about 7 mm from side to side.
A chip of glass popped out of the upper part of the fracture, but the other pieces remained in place.
The distinct blue ring is 3 mm OD and marks the inner boundary of a purple disk surrounding the central burn. The disk appears only in reflected light (which is impossible to photograph with any setup I can manage), suggesting it comes from diffraction in a surprisingly uniform air layer blown between the glass and the plastic polarizing sheet.
Also seen from the rear, the second pulse produced a neater wound:
Laser vs sunglasses – beam rear – B
The blue ring is again 3 mm OD and the image is 7 mm across.
The central red spot probably comes from damage to the polarizing sheet.
The most surprising things, at least to me, didn’t happen:
the glass lens didn’t disintegrate
the laser beam didn’t punch completely through
Protip: Don’t depend on ordinary glasses, even fancy sunglasses, to protect your eyes from CO₂ laser beams.
Well, a shattered lens found beside the road on a walk:
Laser vs sunglasses – focused overview
The battered frame has enough information to suggest they were once rather fancy. At this point, all that matters is they have two glass layers separated by a dark plastic polarizing film, with a gold-ish metallized front glass surface.
I fired the two pulses (on the left side of the obvious crack) at the front of the lens, both at 100 ms / 70% power:
Laser vs sunglasses – overview
Neither pulse penetrated the lens.
The smaller zit was fired in the position shown in the first picture, with the focal point more-or-less at the top surface of the lens. As seen from the front:
Laser vs sunglasses – focused front
The outer part of the damaged area is about 0.5 mm in diameter. The heat around the damage seems to have cleared away all the schmutz on the lens; those things that look like scratches are oily smears and road dirt.
Seen from the rear:
Laser vs sunglasses – focused rear
The rear surface is blistered, but doesn’t have a hole, so I think the beam melted the glass and inflated a cavity along its path.
I then perched the lens in the unfocused beam path, with paper taped over the laser head opening to keep any fragments off the mirror and focus lens:
Laser vs sunglasses – beam front overview
The beam produced the larger scar and also blasted off a ring of crud around the wound, as seen from the front surface:
Laser vs sunglasses – beam front
The beam seems to have shattered a thin layer under the metallization, but didn’t do any deeper damage. The rear surface is undamaged and the paper didn’t have a scorch mark.
They’re not laser safety glasses, but at least they didn’t disintegrate.
Protip: do not lie on the laser platform and stare upward into the laser head, even while wearing fancy polarized mirrorshades.
Mary left the sticky card traps in the onion patch until the last onions came out, clustered them around the leeks, and collected them long after the season was over.
I count maybe twenty flies that might be onion maggot flies or cabbage maggot flies.
The cards protected the onion crop, failed miserably for the leeks, and did nothing for the nearby cabbages. Deploying the cards while planting worked very well, refreshing them after a month continued the protection, but the main fly season seems to end shortly thereafter.
All the sticky cards as a slideshow, starting with the three along the border fence:
VCCG Onion Card – fence A – 2022-11
VCCG Onion Card – fence B – 2022-11
VCCG Onion Card – fence C – 2022-11
VCCG Onion Card – plot A – 2022-11
VCCG Onion Card – plot B – 2022-11
VCCG Onion Card – plot C – 2022-11
VCCG Onion Card – plot D – 2022-11
The cards remain sticky to my fingers, but an adroit fly could skate over the debris field and emerge unscathed.
The Smell of Molten Projects in the Morning 