Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Category: Software
General-purpose computers doing something specific
Anyhow, the Y axis motor position puts the belt too close to one side of the pulley, with no further adjustment possible:
Prusa MK4 Y axis motor mount – as-built
The stepper motor stator laminations are the striped gray area on the far left, the 3D printed motor mount is the striped black area on the right, and the belt pulley is snugged up against the motor as far as it can go on the shaft.
Pushing the motor a little more to the left requires a shim:
Prusa MK4 Y axis motor mount – shim
Rather than fiddle with scanning the motor mount, I imported its STL model from the Prusa MK4 files:
Prusa MK4 Y Axis Motor mount – solid model
Importing the STL into OpenSCAD and converting the motor face into an SVG file is basically a one-liner:
Import the SVG into LightBurn, round the corners a little, set it up for 1.5 mm Trocraft Eco, Fire. The. Laser. and it fits perfectly and stands out nicely:
A glass-top patio table came with our house and, similar to one of the patio chairs, required some repair. The arched steel legs fit into plastic brackets / sockets around the steel table rim under the glass top:
Glass patio table – new brackets installed
The four glaringly obvious white blocks are the new brackets.
The original brackets had, over uncounted years, deteriorated:
Glass patio table – failed OEM bracket
Perhaps disintegrated would be a better description:
Glass patio table – crumbled OEM bracket
Each leg has a pair of rusted 1-½ inch ¼-20 screws holding it to the central ring. As expected, seven of the eight screws came out easily enough, with the last one requiring an overnight soak in Kroil penetrating oil plus percussive persuasion:
Glass patio table – jammed screw
The four legs had three different screws holding them to the brackets, so I drilled out the holes and squished M5 rivnuts in place:
Glass patio table – M5 rivnut installed
Although it’s not obvious, the end of that tube is beveled with respect to the centerline to put both the top and bottom edges on the table rim inside the bracket. In addition, the tube angles about 10° downward from horizontal, which I did not realize amid the wrecked fittings, so the first bracket model failed instantly as I inserted the leg:
Glass patio table – first bracket test
The top & bottom walls of that poor thing were breathtakingly thin (to match the original bracket) and cracked when confronted with the angled tube. I could not measure all the sizes & angles without assembling the table on trial brackets, so getting it right required considerable rapid prototyping:
Glass patio table – failed brackets
Some trigonometry produced a solid model with features rebuilding themselves around the various sizes / angles / offsets:
Glass Top Table – leg bracket – solid model
A sectioned view shows the angled tube position and end chamfer:
Glass Top Table – leg bracket – section view
The OpenSCAD code can produce a sectioned midline slice useful for laser-cut MDF pieces to check the angle:
That eliminated several bad ideas & misconceptions, although trying to balance the leg on a 3 mm MDF snippet was trickier than I expected. In retrospect, gluing a few snippets together would be easier and still faster than trying to print a similar section from the model.
The slightly elongated slot for the M5 screw shows that the original screw holes were not precisely placed or that the tubes were not precisely cut, neither of which come as a surprise. I finally built some slop into the design to eliminate the need for four different blocks keyed to four different legs.
The outer rim, the notch on the bottom, and the tab on the top curve to match the four foot OD glass tabletop, with the inward side & ends remaining flat:
Glass patio table – chunky bracket installed – top
The sector’s difference from a straight line amounts to half a millimeter and improved the fit enough to justify the geometric exercise. The bracket snaps into position with the notch over the table rim and the tab locked in the gap between the glass disk & the rim, although I suspect the weight of the tabletop would keep everything aligned anyway.
The walls are now at least 4 mm thick and, printed in PETG, came out strong enough to survive assembly and some gentle testing. They’re arranged to print on their side to eliminate support under those slight curves and to align the layers for best strength vertically in the finished bracket:
Glass Top Table – leg bracket – slicer preview
The leg cavity and screw hole built well enough without internal support.
They’re relentlessly rectangular and I’m not going to apologize one little bit.
Now to see how they survive out there on the screened porch.
Update: This post seems strangely popular, so the GitHub Gist now includes the STL file in ASCII format. Your library / makerspace / friend can print it, but it probably won’t fit your table, because all tables are slightly different. Print it in TPU and maybe it’ll flex to fit, but ideally you should use the source: install OpenSCAD, tweak the dimensions to suit your table, and get an exactly matching solid model.
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It’s about a foot long, which makes one think of those prehistoric insects flying in dense, oxygen-rich air.
Of course, a Dragonfly needs prey, for which a Mosquito should suffice:
Mosquito – assembled
It’s about five inches from needle tip to tail and would certainly put up a stiff fight.
They’re both made from chipboard, with original model slot sizing being Close Enough that I could just resize the whole thing to fit the available sheets.
Starting from an SVG file set up for 3 mm material, apply the usual optimizations & tweaks to get a usable LightBurn file, then go nuts:
Spider Collection
The big one is two cross-laid layers of corrugated cardboard using up the better part of three Home Depot Large moving boxes:
Spider – LightBurn layout – 2x cardboard
That little bitty grid is the 700×500 mm laser cutter platform, so I just slap a sheet of cardboard in place, update the workspace from the camera, select the next layout, drag it over the cardboard, and Fire The Laser.
The smaller cardboard spider over on the left is built with a single cardboard layer and succumbed to the square-cube law: the legs are entirely too bendy for the weight of the body. Although it’s not obvious from the pictures, both cardboard spiders have a keel plate I added under the body to support most of their weight.
The brightly colored little spiders got a coat of rattlecan paint without any underlying primer and definitely look like that happened:
Spider Collection – detail 2
The edge-lit fluorescent green spider is sized around 2.9 mm material, the clear spider uses 2.3 mm acrylic, and the chipboard one in the background is at 1.8 mm:
Spider Collection – detail 1
The eyes are fluorescent red or green acrylic with concentric circles engraved to catch the light. They’re more effective than I expected, although they won’t look like much after dark.
We now live in a neighborhood with youngsters and Halloween this year will be so much fun …
The WordPress AI image generator caught the general idea of “cardboard spiders”:
Everything is held together by ordinary wood glue, squeezed together for a few moments until the two parts no longer slide around.
One layer of 3.9 mm corrugated cardboard:
Beetle – 1x cardboard
The fancy gold & hologram decorations come from what’s surely non-laser-safe PSA vinyl sheets, cut by offsetting the top layer shapes inward a reasonable amount. The eyes come from random colored paper or painted chipboard.
Two layers of cardboard add up to 8 mm:
Beetle – 2x cardboard
That’s purple paper left over from the layered paper quilt blocks and, obviously, my glue stick hand is weak.
Three layers of cardboard makes each part half an inch thick:
Continuing the theme of slot resizing for various materials:
Elephants – 3.8 and 1.5 mm
The DXF pattern imports directly into LightBurn and requires the usual joining / closing / optimization before all the slots resize in unison. Doing the resize changed the slots from the original 3.0 mm to the 3.9 mm required to convert a cardboard moving box into a pachyderm.
The leg sections turned out to be a bit too thin for corrugated cardboard, so the corrugations came loose from the surface sheets, although the tail looked much more realistic. Stipulated: corrugated cardboard is the wrong material, but I really didn’t need a big MDF elephant looming over everything else.
The smaller elephants, both in 1.5 mm thick materials, come from a global resize applied through the LightBurn Numeric Edit toolbar:
LightBurn Numeric Edit – percent resize
The ratio makes the slots become the new size, with the entire rest of the design scaled around them. This works if you don’t much care about the overall size, but is rare in actual practice where you need a model “that big” with the slots fitting “that material”.
But the pieces just slid together:
Elephants – 1.5 mm detail
I put dots of cyanoacrylate in the acrylic joints, although the vapors scarred the surface enough to remind me why that’s the wrong adhesive for the job when you care about surface quality. Dots of wood glue hold the chipboard elephant together, with a quick shot of clear rattlecan paint to knock down the smell of the charred edges; I’d say the color came out about right.
The Smell of Molten Projects in the Morning 