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.
Having grossly exceeded the Gentec ED-200 maximum power spec, I wasn’t surprised to see this when I finally tucked it back in the drawer:
The 0.5 mm scale suggests the damage came from a defocused 2 mm beam or the hot central part of a larger beam, but I obviously wasn’t paying enough attention at the time.
The rest of the surface seems undamaged, so this may have been one of those inadvertent long-duration pulses or several shorter shots in one spot.
The proof of concept coaster might suffice for a shot glass, but my morning tea comes in a 20 ounce mug with a much larger footprint.
So, back to the Basement Shop, where a laser-cut and -engraved layout guide helps arrange and carry some suitable fragments:
As before, scan the bottom of the fragments and wrap selections around them:
Apply the usual operations to get a suitable mask:
Fire the laser to cut the chipboard test template holding the fragments, then a white octagonal acrylic base plate and a transparent acrylic layer surrounding the fragments, and:
Mix up some pourable epoxy, smooth it over the base plate, squish the transparent layer atop it, use the tape (sticky side up) to hold the two layers in alignment, and gently insert the fragments:
I eased some epoxy around the perimeter of each fragment with a pipette in an attempt to reduce the glass-sliver hazard:
Yes, that’s on top of the protective paper, because then I can whisk the paper off to reveal the pristine surface around each fragment:
As with the smaller coaster, the epoxy penetrates the fractures and reduces the shattered appearance. Mary suggests tinted epoxy would produce an interesting effect and I’ll try that the next time around.
Because the smashed glass came from our neighbor’s lawn, it carried a bit of dirt and debris onto the playing field:
Seen through the edge of the coaster, the uneven surface of the epoxy fill around the fragments shows up clearly:
The top of the glass stands half a millimeter above the transparent acrylic. I knew that would happen and wanted to see how the bottom of the mug interacted with the epoxy-coated sides:
As it turned out, the epoxy coating wasn’t quite good enough to prevent tiny slivers from chipping off and, in the cold light of day, the pale-green-ish tinted glass didn’t stand out well against the white background.
So I taped up the perimeter, leveled the base, mixed up another batch of epoxy, added two drops of opaque black dye, and poured just enough to level the surface with the glass:
Introducing the meniscus to Mr Belt Sander put a bevel around the edge and finished it off well enough:
The Squidwrench logo looks a bit battered after three and a half years of trips through the dishwasher, although I didn’t expect it to last nearly this long.
There’s still a slight upward tilt around the perimeter, but it meets my simple requirements and the fragments definitely look better in black. The white base sets off the fragments, but a clear plate takes advantage of their transparency; a mirror sheet might be even more interesting.
If you’re a particularly sharp person, these may accentuate your wardrobe:
They’re fragments of smashed tempered glass, epoxied into laser-cut disks, with a ring providing some structural support. Although it’s hard to tell from the photos, the fragments sit flush with one side of the disk, which is likely the side you want closest to your carotid artery:
Each chunk consists of a few smaller cuboids, so you get internal reflections from the minute air gaps between them. They’re not diamonds, but they’re surprisingly glittery in the proper light. Bonus: you can see right through!
The “gold” band around the disk is a beading ring held in a notch engraved around both disks:
The smaller ring is 12 mm OD, the larger is 25 mm, with 16 mm (the descriptions says 15, but ya get what ya get) and 20 mm available for other glass fragment sizes.
The engraved recess (green) is slightly larger than the OD to allow the perimeter cut to proceed through a thinner section:
Cross-hatch engraving puts a steep edge all around the recess, so the ring fits with just a little slack and turns freely around the disks.
You will, of course, have different glass fragments requiring different shapes, but the outlines came from the same process I used to make the palette organizing the fragments:
You (well, I) can just import that layout, copy the outline of the chunk to be used, then delete the rest. Mirror the outline so the engraved sides of the disks fit together around the chunk, position symmetrically in the template halves, and fire the laser.
Affixing the fresh-cut disk and its glass chunk to a strip of Kapton tape (sticky side up) holds them in proper alignment and prevents the epoxy from leaking out the bottom:
With everything lined up, run a small bead of epoxy around the chunk, squish the top disk in place, and line up the notches. When the epoxy cures, peel the earring off the tape and slide a jump ring into the notch.
As a finishing touch, you’d add a suitable ear hook or stud, but I think it’s fair to assume anything from Amazon would consist of the finest arsenic-plated plutonium and be completely unsuitable for skin contact. Neither of us have any piercings, so I cannot provide enticing action photos.
The 25 mm versions failed because I made the outlines such a snug fit around the chunks they didn’t quite fit:
Protip: do not attempt to coerce two rigid bodies into alignment by applying firm pressure, particularly when one of them is already-broken glass.
The small earrings weigh 0.7 g each and a 25 mm one (well, the parts for a large one) comes in a bit over 3 g, plus whatever hardware goes in / on / around your ear.
This was (obviously) an exercise in small-scale laser machining, rather than a venture into haute couture. In the highly unlikely event you can’t live without a pair of custom-designed high-impact earrings, I’ll shut up and take your money … let me know if you want little or big. Black is the new black; I do have other colors, but who are you kidding?
The SVG images as a GitHub Gist:
Having a myriad small glass fragments and an idea for their use created the problems of organizing the pieces while not losing them under the bench.
As with the shattered shot-glass coaster, start by lining up the suspects on the scanner:
Blow out the contrast, flip right-to-left, then mask them en masse:
Delete the images (inside their selection masks) to create a binary mask:
Have LightBurn trace the binary images, wrap a rounded rectangle around the lot of them, duplicate the rectangle as a base plate, then fire the laser:
They’re not secured in their sockets, but they won’t fall out unless I fat-finger the whole affair:
The thing that takes getting used to: the whole process was about two hours of wall clock time from start to finish, with a leisurely breakfast and KP in the middle.
Given a few pounds of smashed tempered glass:
Lay some pieces atop an acetate sheet (to prevent scratching) on the scanner, grab the whole thing, then isolate an interesting chunk:
Next time: flip the image left-to-right to match the glass piece as seen from the top, because the scanner was looking at the bottom.
The weird purple background started as black, but blowing out the contrast while ignoring the color mis-correction makes the next step easier.
Trace around the perimeter with Scissors Select, clean up the result in Quick Mask mode, expand the selection by a few pixels to improve clearance, then turn it into a two-color image mask:
Import the mask into Lightburn, trace it into vector paths (which is trivially easy and accurate given such a high-contrast image), then cut a chipboard prototype to make sure it fits:
Clean up any misfits, test as needed, cut the inner shape and outer perimeter from 1.5 mm black acrylic, cut just the outer perimeter from 3 mm clear acrylic. Put the piece of black acrylic matching the glass shape into the scrap box.
Mix up a few milliliters of clear pourable epoxy, butter up the clear acrylic, lay the black acrylic on top, line up the edges, then gently place the shattered glass into the cutout:
Next time: apply gentle pressure, perhaps through a flexy sheet, to ensure the entire glass surface contacts the epoxy layer while squeezing out the bubbles. This will surely skate the glass across the acrylic, so don’t leave it unsupervised.
The relatively clear areas show where epoxy eased its way into the cracks between the granules; there is no correlation between the air bubbles and unfilled cracks. The epoxy had the viscosity of warm honey and I didn’t expect it to flow so easily, but it doesn’t affect the outcome.
Wait for a day, no matter how hard that may seem, for the epoxy to cure. Leave the small cup holding the remnants of the mixed epoxy nearby so you can test the cure without disturbing the Main Event.
The bottom looks pretty much like the top:
The shattered edge reflects off the bottom of the clear acrylic, as seen through the side:
Matching the perimeter to the fragment would be interesting, despite my low-vertex-polygon fixation.
It could become a paperweight or a (shot glass) coaster.
It seems two months of sunlight will fade laser charred MDF down to its original state:
That’s through a thick layer of indoor urethane sealant slathered over MDF without any surface prep. Obviously, not removing the char had no effect on the outcome. On the upside, the urethane did a great job of protecting the MDF from rainfall.
So. Back to the shop.
Lacking wider masking tape, two strips of tape laid along a cut-to-suit slab of fresh MDF will serve as a paint mask:
Belatedly I Learned: cut the tape close to the edge, then fold it under so the autofocus pen can’t possibly snag it en passant.
Shoot the entire surface with a couple of black enamel rattlecan coats:
Yes, the engraved areas look reddish, most likely due to another complete lack of surface prep. Perhaps brushing / vacuuming / washing would remove some of the char, but let’s see how it behaves with no further attention.
Peel the tape, weed the letters / antlers, slather on a coat of urethane, and it looks downright bold:
Of course, if those two tape strips don’t exactly abut, the paint produces a nasty line:
Should you overlap the strips a wee bit to ensure cleanliness, the engraved surface will then have a noticeable (in person, anyhow) discontinuity due to the laser losing energy in two tape layers, which wouldn’t matter in this application. We defined the few paint lines as Good Enough™ for the purpose; a strip of absurdly wide masking tape is now on hand in anticipation of future need.
Burnishing the tape might have prevented paint bleed around the engraved areas:
But, given that I was painting raw / unfinished MDF with an unsmooth surface, burnishing probably wouldn’t produce a significantly better outcome.
By popular request, the new signs sit a few grids lower on the gates:
Perhaps these will outlast the garden season …
The air assist pump sits in the right rear of the OMTech laser’s main compartment:
Where it is, of course, exposed to all the usual dust / fragments / fumes / smoke generated by laser cutting & engraving, enhanced by my attention to getting good air flow over the platform. The picture shows the base plate in as-delivered condition, which it will never resemble ever again.
The problem: any crud in the air can clog the pump or contaminate the laser focus lens.
Four screws into threaded holes hold the pump to the base plate, secured with jam nuts on the outside.
The air inlet is a round fitting centered on the bottom of the pump housing:
You’ll note the out-of-focus crud scattered on the base plate.
The general idea is to drill a hole through the base plate, put a snorkel on the inlet, and have it inhale fresh, relatively clean, basement air from outside the cabinet. The trick will be not touching the base plate with anything solid, because the pump vibrates like crazy; its four squishy standoffs do a great job of isolating the tremors from the base screwed to the laser cabinet.
Having a few other things going on at the moment, I just laid two generous wads of cheesecloth where they can filter the bigger chunks out of the air stream:
The air flow meter says the pump still delivers 12 l/m to the nozzle, so the cheesecloth has no effect compared to four or five feet of 4 mm ID tubing.
A doodle summarizes the inlet fitting dimensions:
That looks like a 3D printed disk with a snout for a short air hose should do the trick, with a thin gasket sealing the disk to the fitting.
Now I can throw that piece of paper out …
The Smell of Molten Projects in the Morning 
