Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
A sheet of craft adhesive holds them together; stick a generous rectangle of adhesive on the cork, then cut them at the same time. However, given the irregular perimeter, it’s basically impossible (for me, anyway) to align the cork + adhesive with the printed frame.
A single-use fixture made from corrugated cardboard make that task trivially easy:
Printed Coaster – cork alignment fixture – detail
The LightBurn layout shows the cork layer and the two fixture pieces:
The cork shape is offset 0.5 mm inward from the Perimeter shape, but I found offsetting the cardboard cut by only 0.3 mm inward produced a snug fit around the cork. The other piece of cardboard gets cut with the exact Perimeter shape and no offset, with the laser kerf providing just enough clearance for a very snug fit on the printed shape.
Align the two pieces of cardboard by eye to match their inner shapes as shown in the picture, tape them together, and the fixture is ready. In principle, the outer edges should exactly coincide: Trust, but verify.
Peel off the craft adhesive paper and put the cork in the bottom of the fixture. The cork comes off a roll and really wants to roll up again, making the masking tape holding it flat mandatory:
Printed Coasters – cork alignment template
Yes, that’s a different coaster.
Flip the fixture over, drop the coaster in place, press firmly together, peel the tape, and pull out the finished coaster:
Printed Coasters – white PETG finished
The fixture goes in the recycling bin, as those fragments will never pass this way again.
Create the perimeter path as an offset around all the fragments in LightBurn
Because the fragments have irregular shapes and spacing, creating the perimeter path may also produce small snippets of orphaned geometry which must be manually selected and deleted. I also edit the path to remove very narrow channels between adjacent fragments.
Which is why you can’t generate that path automatically:
Printed Coaster Layout – 100 mm Set G – LightBurn perimeter geometry
Because LightBurn doesn’t have the ability to name the various paths, the next step requires Inkscape. After importing the LightBurn paths saved as an SVG, group all the fragments and name the group Fragments, then name the perimeter path Perimeter:
Printed Coaster Layout – 100 mm Set G – Inkscape layer and IDs
Inkscape still crashes unpredictably while doing what seems to be a simple process, which may be due to the tremendous number of points in the hand-traced fragment outlines. Unfortunately, simplifying the curves in either LightBurn or Inkscape tends to round off the extreme points and increases the likelihood of the fragment not fitting into its recess.
OpenSCAD generates all the other features in the solid model with paths plucked from that file:
include <BOSL2/std.scad>
fn = "Printed Fragment Coaster - 100 mm Set G - Inkscape paths.svg";
FragmentThick = 3.8;
BaseThick = 1.0;
RimHeight = 1.0;
union() {
linear_extrude(h=BaseThick)
import(fn,id="Perimeter");
color("Green")
up(BaseThick)
linear_extrude(h=FragmentThick)
difference() {
import(fn,id="Perimeter");
offset(delta=0.2)
import(fn,id="Fragments");
}
color("Red")
up(BaseThick)
linear_extrude(h=FragmentThick + RimHeight)
difference() {
offset(delta=2.5)
import(fn,id="Fragments");
offset(delta=1.2)
import(fn,id="Fragments");
}
}
The Perimeter path defines the overall shape of the coaster as a 1.0 mm thick slab, visible as the white-ish line around the edge and at the bottom of all the fragment recesses.
Atop that, the green shape is the same Perimeter shape, with the Fragment shapes removed after the offset() operation enlarges them by 0.2 mm to ensure enough clearance.
Finally, the red walls containing the epoxy above each fragment are 1.3 mm wide, the difference of the two offset() operations applied to the Fragments.
Because the outer edge of the wall is 2.5 mm away from the edge of its fragment:
The Perimeter path must be offset at least 2.5 mm from the Fragments in LightBurn. I used 4.0 mm to produce a small lip around the outside edge of the coaster.
The fragment shapes must be placed at least 5.0 mm apart to prevent the walls from overlapping. I set Deepnest to exactly 5.0 mm spacing, but you can see a few places where the fragments come too close together. I think this happens due to an approximation deepnest uses while rotating the paths, but it may be better to manually adjust the errant fragments than increase the average space.
While this still requires manually tracing the glass fragments and fiddling a bit with Inkscape, the overall process isn’t nearly as burdensome as getting all the offsets correct every time.
However, some oddities remain. OpenSCAD produced this result during the first pass through the process for this coaster:
Printed Coaster Layout – 100 mm Set G – spurious point
As far as I can tell, the spurious point came from a numeric effect, because telling Inkscape to store only five decimal places in the SVG file reduced the spike to the small bump seen in the first picture. I cannot replicate that effect using the same files and have no explanation.
This should have been trivially easy and turned into a nightmare.
The problem to be solved is generating paths around fragments for the various recesses / reflectors / lips / rims / whatever. This clutter collector was a test piece:
Smashed Glass Clutter Collector – overview
The corresponding paths:
Printed Clutter Collector – Inkscape layers
Which was how I convinced myself I didn’t need all those paths to make the thing, but that’s why it’s a test piece.
Anyhow, Inkscape has a remarkably complex and fiddly way of generating precise offsets:
Select a path
Hit Ctrl-J to create a Dynamic Offset path
Drag the offset path away from the original in any direction for any distance
Hit Ctrl-Shift-x to fire up the XML editor (!)
Change the offset path’s inkscape:radius property to the desired offset
During the course of working that out, I discovered Inkscape 1.4.2 is incredibly crashy when creating and dealing with offsets, to the point that I simply gave up trying to do that.
LightBurn has no trouble creating a path at a specific offset from another path and can export the result as an SVG file. You then use Inkscape to set the path IDs so that OpenSCAD can import them by name for a specific use. Although Inkscape isn’t entirely stable doing even that seemingly trivial task, it’s usable.
For reasons I do not profess to understand, setting the name of a path sometimes does not set its ID property, which is required by OpenSCAD to extract it from the SVG file. Instead, you must verify / set the ID using the path’s Object Properties window:
Save that, import it into PrusaSlicer, pick the filament, and print it out.
While the printer buzzes away, use LightBurn to cut a shiny blue metallized paper reflector and a cork base using the appropriate paths; presumably you set those paths to LightBurn layers corresponding to the various materials. The Inkscape file has those paths with their names, because … why not?
To assemble:
Cover the bottom of the recess with epoxy
Squish the reflector in place with epoxy oozing around it on all sides
Cover the reflector with epoxy
Squish the fragment atop the reflector with epoxy oozing around it on all sides
Fill the recess level with the lip inside the perimeter wall
Pop bubbles as needed
When it’s cured, stick the cork sheet on the bottom
Note that the OpenSCAD program uses the path geometry without question, so it’s your responsibility to create them with the proper offsets and names.
While all of that to-ing and fro-ing works, in the sense that I did make a rather nice clutter collector, it’s entirely too complicated and fiddly to be useful. Instead, I can now generate a coaster from just the fragment outlines and the coaster’s outer perimeter, a straightforward process which requires a bit more explanation.
Cleaning the baseboard radiator fins before moving the houseplants back to their winter abode by the living room window made sense, so I took the trim covers off and vacuumed a remarkable accumulation of fuzz off the top and out from between the fins. The covers had an equally remarkable accumulation of sawdust along their bottom edge, apparently deposited when the previous owners had the floor sanded before they moved in a decade ago.
If you happen to live in a house with baseboard radiators, I’m guessing you never looked inside, because nobody (else) does.
Anyhow, the radiator fins should rest on plastic carriers atop the bent-metal struts also supporting the trim covers, so that they slide noiselessly when the copper pipe expands & contracts during the heating cycle. Over the last six decades, however, the plastic deteriorated and most of the carriers were either missing or broken to the point of uselessness:
Baseboard Radiator Sled – old vs new
The shapes on the bottom are replacements made with a 3D printed base (“sled”) and a chipboard wrap around the radiator preventing the fins from contacting the strut:
Baseboard Radiator Sled – OpenSCAD show
Although it was tempting to 3D print the whole thing, because plastic, I figured there was little point in finesse: chipboard would work just as well, was much faster to produce, and I need not orient the shapes to keep the printed threads in the right direction.
The Prusa MK4 platform was just big enough for the number of sleds I needed:
Baseboard Radiator Sled – printed
The sleds along the left and right edges lost traction as the printing progressed, but everything came out all right.
The OpenSCAD program also produces 2D SVG shapes for the chipboard wraps and adhesive rectangles sticking them to the sleds:
Baseboard Radiator Sled – OpenSCAD SVGs
Import those into LightBurn, duplicate using the Grid Array, Fire The Laser, then assemble:
Baseboard Radiator Sled – assembly
The slits encourage the chipboard to bend in the right direction at the right place, so I didn’t need any fancy tooling to get a decent result.
A few rather unpleasant hours crawling around on the floor got the struts bent back into shape and the sleds installed under the fins:
Baseboard Radiator Sled – installed
Protip: Gloves aren’t just a good idea, they’re essential.
The trim cover presses the angled chipboard where it should go against the fins. The covers carry shadows of the plastic carriers, suggesting the clearance was tighter than it should have been and thermal cycling put more stress on the plastic than expected. We’ll never know.
Although I’ll make more for the other baseboards as the occasion arises, I hope to never see these again …
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The laser-engraved guide lines confused GIMP’s edge detection to no end.
It came from a large sheet of 1 mm acrylic, formerly a poster cover, bearing scars of its long history in the “might be useful someday” stash. I wondered if I could remove enough scratches and scuffs to ease GIMP’s workload.
Stipulated: I am a cheapskate.
Laser-cut a suitable sheet and sand both sides with 220 grit paper to what looked like a uniform surface:
Acrylic polishing – 220
Continue scrubbing with 400, 800, 1000, 1500, and 3000 grit papers:
Acrylic polishing – 3000
Massage it with Novus Polish 3, 2, and 1:
Acrylic polishing – Novus 1
At best, it’s more translucent than transparent and definitely not an optical-quality polishing job:
Acrylic polishing – translucency
Fortunately, I need not care about the edges, because it goes in a square frame with a circular cutout.
Tape it into that cardboard frame, scan it against a black background, and blow out the contrast to show I should have started with 100 grit paper and paid more attention to that “uniform surface” thing:
Acrylic polishing – scratches
In use, though, it doesn’t look all that bad:
Fragment layout – 5in Set B – scan tweaked
Come to find out those glittery cracks between all the cuboids still confuse GIMP’s edge detection, but at least hand-tracing the outline is easier without all the lines.
The entire “polishing” series as a slideshow for your amusement:
For reasons not relevant here, after Having Been Advised to not walk barefoot on our wood floors, I picked up a pair of beach / pool sandals with comfy soles. Although they have a white logo, they’re black and essentially invisible in the dark when I need them most.
Start by taking a photo of the logo on the clamped-flat upper strap:
UnderArmour logo – flattened
Use GIMP to select the white area, clean it up a little, convert the selection into a path, export it as an SVG file, import into LightBurn, scale to match reality, and Fire The Laser:
UnderArmour logo – GITD tape cutting
That’s a roll of glow-in-the-dark tape which is almost certainly a lethal combination of PVC and phosphorescent stuff, so hold your breath while it cuts.
It’s “actually a “kiss cut” through the tape, but not through the backing paper, letting the whole thing hang together after the operation.
Peel-n-stick on the (still flattened) sandals, expose them to light, and It Just Works:
UnderArmour logo – glowing
The fit isn’t perfect, perhaps due to insufficient flattening, but it’s close enough for my simple needs.
The Smell of Molten Projects in the Morning 