Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The Chimney Swallows block from page 128 of Beyer’s book:
Chimney Swallows – Beyer 128
The tool (blue & orange) and top cut (red) layers:
Chimney Swallows – LB layout
The long radial blue tool lines simplified selecting them when mirroring / duplicating the cut polygons around their symmetries. The orange tool circles aligned various midpoints / vertices / features during construction.
The inward curve along the outer edge started as a triangle with a node at about the middle of the curve. Deleting that node left the remaining two sides overlapped, but dragging one of them to match the curve worked OK. There’s probably a better way.
That curve defines the outer edges of the shapes along it, so I drew polygons from the corner intersections and dragged the outer edge to match the curve at high zoom.
The shape remains selected after dragging the side, which meant I could immediately apply a 1 mm inset to create the cut lines.
To my surprise, the swallow bodies are straight-sided polygons!
After taking advantage of all the symmetries, knock out the shapes defining each layer:
It looks more like flowers than fireworks to me, but there’s no accounting for taste.
Deploy enough 2 mm circles to catch the flower’s radial symmetry:
Pyrotechnics – LB layout
During the process of building the layout, a big circle positioned the cups at the base of the flowers, another delineated the joint between the cups and the petals, and more little circles caught the intersection of those circles with the petals. All that was for visualization and positioning, as you only draw one flower shape, then duplicate it around the pattern.
Although the cups and petals are surely circular arcs, it’s easier to draw a closed line triangle around the intersections, then pull the midpoint of a line into an arc (Bezier curve!) matching the pattern Closely Enough™ at high zoom. Because the arcs end at the intersection points based on circular arrays of points, they’ll all match up when they’re duplicated around the pattern; in fact, you need only one side of one petal, mirror it around the midline, and away you go.
Then the magic happens:
Pyrotechnics – LB tool insets
Which is easier to see without the original shapes:
Pyrotechnics – LB insets
Pick one of the closed shapes, apply the Offset tool to shrink it by 1 mm, duplicate as needed, and you get the outlines of the regions to cut with 2 mm between them. Plunk those shapes on a cutting layer, add the outer frame with locating holes for the fixture, and it’s ready to cut the top layer from black paper:
Pyrotechnics – LB cuts
Knock out the cuts for each sheet of paper in the stack:
Pyrotechnics – LB paper cuts
Then Fire The Laser™:
Layered Paper – Pyrotechnics – Beyer 132
That was a nearly random selection of colors, but it’s hard to go wrong.
This seemed like an appropriate use for the stack (well, several stacks) of colored paper I’ve accumulated over the years.
The illustration in the book is apparently a photograph of a quilt block Beyer put together, so I had to reverse-engineer the Platonic Ideal Block from the image:
Mariners Compass – minimal shapes – LB layout
Fortunately, after a bit of fiddling around, I could take advantage of the radial symmetry to duplicate most of the fundamental shapes, so producing the layout really wasn’t all that difficult:
Mariners Compass – LB layout
The blue tooling lines (upper left) run along the centers of what would be seams in a fabric block, with 2 mm circles defining the endpoints for ease in snapping the lines.
This being the first block I attempted, I did it all wrong. LightBurn can form the convex hull over a group of shapes, so I just selected pairs of circles, created the hull, and iterated for the minimal shapes required to generate the whole design. That produces the basic layout, but what you really want is the collection of shapes between those hulls that define the actual cutouts, which appears in the lower left image.
Don’t do it that way, as explained tomorrow with a different block.
With all the shapes in hand, you duplicate them for all the paper layers you need, removing the shapes corresponding to the color of each sheet. Sheets lower in the stack have fewer cutouts, with the pattern in the lower right being second from the bottom.
The four holes in the corners fit over rivnuts in a fixture aligning the sheets in a tidy stack:
Layered Paper – alignment fixture
Yes, that’s a blooper sheet.
All in all, it’s easier than I expected to get nice results.
It’s a test piece with adhesive sheets between acrylic layers:
Layered Acrylic Desk Junk Collector – edge detail
From top to bottom:
Acrylic 4.3 mm – sidewall to corral the junk
Acrylic 1.5 mm – top plate
Acrylic 2.4 mm – two layers
Acrylic mirror 3 mm
Cork 2 mm – PSA backing
The pair of 2.4 mm layers add up to just an itsy more than the 4.8 mm thickness of the shattered glass atop the mirror. Unlike previous epoxy sealed coasters, the glass sits on a sheet of 3M LSE adhesive film to keep the pieces together, with the top 1.5 mm acrylic layer containing any slivers. Because there’s no epoxy involved, the project is finished with no muss, no fuss, no curing time, and no drippy edges.
The geometry comes from a scan of the glass piece:
Desk Clutter plate – smashed glass – Quick Mask
That’s the GIMP Quick Mask result of manually drawing around the perimeter with the center of a 25 pixel diameter pencil, thus creating a 12 pixel gap to ensure the glass will fit inside the cut shape: at 300 dpi, the 12 pixel gap is about 40 mil = 1 mm wide. Slightly less would work as well, although I’ve discovered some of the glass cuboids have non-vertical walls sticking out to the side above the scanner’s depth of field.
Scribbling over the interior with a bigger pencil clears it out and a few fill operations produce a binary mask perfectly suited for LightBurn’s Image Trace tool:
Desk Clutter plate – smashed glass – binary mask
Trace that outline into vectors, throw away the mask, and use the outline for a conformal cut.
The rings of acrylic and adhesive are 3 mm wide, generated from the outline by offsetting it 3 mm outward:
Desk Clutter plate – LB perimeters
The tooling circle around the perimeter simplifies drag-and-drop alignment, because the geometric center of the perimeter shape isn’t quite in the middle of where you’d (well, I’d) want to align it. Grouping the outline with the circle keeps the center snap point where it should be.
Narrow rings of adhesive sheet turned out to be even more unmanageable than I expected. Perhaps a better way:
Cut the ring with tabs holding it to the center area
Stick the ring + center to vinyl transfer tape
Peel the protective paper off the adhesive ring
Stick the acrylic ring atop the adhesive ring
Sever the tabs to release the adhesive ring
Peel the transfer tape off the ring
The “adhesive tape sheets for craft” are paper-based, rather than a plastic film, and are neither transparent nor durable. I used it mostly to get an idea of how well it sticks to acrylic, as it’s primarily intended for paper crafts.
The 3M LSE backing layer is plastic and the sheet becomes nearly transparent as the glass squishes down, although you wouldn’t want it on a mirror where you cared about the optical quality of the reflection. Underneath a chunk of smashed glass, it’s just fine.
All in all, it turned out well.
Next: how long does that craft adhesive last in abnormal conditions?
It’s the sheet of 3/8 inch = 9 mm vintage acrylic that Came With The House™ and what you see is the relatively unwarped result of several months of pressure. The wood sheet in front puts the left edge mostly flat on the platform, with the steel disk weighting the rear end down; the front end sticks out through the laser’s pass-through door.
The general idea was to cut a rectangle that would be flat enough for the shapes I actually needed:
Blockface grip cutting
They’re grips for a set of Blockface printing shapes. The alert reader will note the rectangle sits atop three spikes, not the usual four; it was flat enough for the purpose, not actually flat.
The OMTech laser claims to be 60 W, but has an over-amped 50 W tube that’s barely adequate for the task. The cuts required two passes:
5 mm/s @ 90% cuts almost all the way through
10 mm/s @ 90% clears the cut enough to have some shapes drop out and the others be easily pushed through
Cranking the tube current that high isn’t recommended practice, either, but sometimes ya gotta do what ya gotta do.
To my utter astonishment, the rubber cuts did not smell like a tire fire and the neighbors did not rise up in arms.
I cut several sets of grips / foam / rubber and sent them off for final assembly. The recipient seems delighted with the results and has been hand-printing up a storm.
Trying a sequence of offset and raster filling produced a credible 0.5 mm deep inlay pocket in a chunk of acrylic:
Earring samples – veneer spade recess
The odd pattern inside the pocket comes from the offset fill:
Veneer spade pocket – LightBurn preview
Combining the two fill patterns produces a smoother bottom in the pocket, but it’s a good thing nobody will ever see it from the back side, because the offset fill concentrations chew through the entire 3mm sheet.
A spade-shaped adhesive sheet bonded the veneer into the pocket, after which I sanded the surface flat with 200 grit sandpaper and hit it with some polyurethane sealer. Next time I’ll knock the finished surface flat with 400 grit paper.
The gray acrylic disk has a rebate around its rear rim for the “gold” ring, with the adhesive disk gluing the black disk to the front:
Earring samples – veneer spade parts
Which looks like this when it’s stuck together:
Earring samples – veneer spade side view
I don’t like the raggedy surface of the rebate above the ring, although it’s not too awful in person.
Having gotten reasonable results with the acrylic pocket, I cut an acrylic spade and stuck it in place with another bit of adhesive sheet, leaving it standing proud of the surface:
Earring samples – veneer spade acrylic
The red earring used up one of the hundred slugs left over from the capsule plate; I’m ready for a surge in demand.
The adhesive sheet is workable in disk form, but the spade shape is entirely too fiddly. A dab of acrylic adhesive would likely work just as well and be easier all around.
The Smell of Molten Projects in the Morning 