Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The two on the left are the original snowflakes with interchanged innards and, perforce, no kerf compensation.
The upper-left coaster has a wood flake surrounded by acrylic, which makes a sharp clack when you set a glass down on it. The wood surrounds emit a much more pleasing clunk.
The next two have 0.1 mm compensation applied to their acrylic snowflakes, which produces snug fit (original on the left, compensated on the right):
Snowflake Coasters – kerf corr 0.0 vs 0.1 mm
Applying 0.2 mm compensation makes the flakes impossible to push in, so the true compensation is somewhere just over 0.1 mm. I think you could optimize for a specific wood and acrylic combination, but, as with 3D printing, any change requires something different.
The little arrowhead shapes tend to get lost, so collecting them on a strip of tape while you’re hunting in the chip tray helps:
Snowflake Coasters – plywood cutouts
The dark flake on the right got a coat of walnut stain, as did the two darker coasters in the first picture. It looks better in person than in the photo, although Mary still thinks the lighter wood sets off the white acrylic just fine.
The two large (120 mm OD) coasters fit my 20 ounce mugs, with the Nanook Memorial Coaster in the lower right.
The rather battered library card on the bottom has been rattling around on Mary’s keyring since late in the last millennium:
Library card tags – front
I made the one on the top as a replacement, because Mary wanted one, but the library no longer issues keyring cards these days.
The front surface was laid out in The GIMP, inkjet-printed on good paper, cold laminated, laser-cut with LightBurn’s Print-and-Cut process, then affixed to the acrylic tag with really good double-sided tape:
Adriance Card – LightBurn PnC layout
I cut and applied the tape after cutting the tag, but the next time around I’ll apply the tape to the stock and cut both together to improve the edge alignment.
The smaller text uses dot mode and the bars & number are engraved:
Library card tag – detail
In retrospect, it’s painfully obvious the engraving passes should run parallel to the bars, rather than perpendicular to them.
The barcode uses Codabar encoding generated with a Codabar font. I scaled the graphic block slightly larger than the original in the hope of making it more readable.
I determined the start and stop characters by trial and error; for this card, they’re A and B. Which could, perhaps, stand for Arlington Branch, but might equally well be coincidence.
It worked perfectly on the first scan at the library counter and apparently went entirely unnoticed. I trust duplicating a library card does not constitute a federal offense.
For what should be obvious reasons, however, I’m not posting the LightBurn layout.
The rattlecan chipboard coasters having passed their Best Used By dates, I figured a more durable seasonal version was in order:
Snowflake Coasters – overview
I laid out the design with the intent of cutting an acrylic snowflake with a bit of compensation to fit snugly into a plywood background:
Snowflake Coaster – LB layout
At the last moment I realized I could just cut two of the patterns on the left, swap the snowflakes, and get two coasters with very little scrap:
Snowflake Coasters – detail
Mary thinks the gap between the snowflake and the background looks OK. I’m not convinced, but studying the results suggests applying enough kerf compensation to close the largest gaps would results in the rest of the flake not fitting into its socket. Plus, of course, you’d have more scrap.
Embiggening the small dagger-shaped pieces around the center would be an improvement. Perhaps cutting those as a separate operation after arranging them in a corner would work.
Protip: Align the grain in those daggers with the rest of the plywood, because It Will Be Very Obvious if you don’t.
Applying a nice wood stain / finish to the plywood, perhaps before cutting it out, would certainly improve the result.
Invisible on the bottom: self-adhesive cork disks eliminating the need to glue the pieces to something else. I had thought of a blank plywood or MDF disk, but came to my senses just in time.
The original SVG fell with a blizzard from one of the many SVG snowflake generators out there. Because LightBurn uses only the stroke centerlines of SVG images and ignores the stroke width, it required some tweakage before becoming a coaster.
After saving an SVG flake from the blizzard, fire up Inkscape:
Import the SVG file
Center it in whatever page you’re using
Ungroup the flake from the frame (if it has one)
Delete the frame to leave only the flake
Select the flake
Invoke Path → Stroke to Path
Save as an SVG image under a new file name
Then fire up LightBurn:
Import the tweaked SVG file
Assign a layer with line (rather than fill) parameters
The rattlecan chipboard versions came out pretty well, because I’ve already explored much of the error space. The two-tone berries and leaves received Sharpie contrast touchup. They’re all in constant use on the kitchen table!
The wood veneer version over on the right looks surprisingly good (in person, anyway) for being a complete faceplant. The narrow sections suffered severe burning and fell apart where the grain runs perpendicular to the cut. The highlight spots for the berries fell through the honeycomb table and vanished in the chaff. Sanding the whole mess flat scuffed off most of the smudges, although I couldn’t bring myself to slather it with polyurethane.
The bright holly on the left is mirror-back acrylic pressed into a 3 mm deep (!) recess engraved in more scrap paneling:
Holly Coaster – mirror
I hand-painted the colors by scribbling Sharpie onto areas where the mirror backing was engraved away. A sheet of aluminized Mylar below the acrylic reflects some light back through the colors to make them slightly brighter.
As I recently learned, applying alcohol to laser-cut acrylic produces almost instantaneous stress-cracking, which accounts for the decorative crackle finish around the perimeter:
Holly Coaster – mirror flaws
The surface flaw beyond the berry over on the right apparently came from an acrylic fume explosion in the honeycomb below it, strong enough to torch the protective plastic film. Given that I was starting with a scrap mirror fragment, I didn’t perch it up on spikes, which is pretty much required to prevent such events.
The wood coasters have mmmmm excellent upside potential, but it’s obvious I have not yet mastered my craft.
Mary made a neck cozy based on a Craftsy description using a pattern I’d extracted from the low-res photo and rescaled to the proper size. The perimeter came out grittier than I like, but the laser had no trouble chopping it from a sheet of paper, and she cut smoothly around the lumps:
Neck Cozy mask – right
It looks better on her, but you get the general idea:
Neck Cozy – rev 1 finished
After some experience, however, she wanted to lengthen the top and bottom seams to improve the way it draped, which meant I had to modify the extracted pattern. The original pattern in the Craftsy photo was hand-drawn (which is perfectly fine) and the two halves were of two different sizes; we decided to work with the left half and produce a symmetric result.
Rather than fiddle with the bitmap, I drew a rectangle around the outside of the left pattern mask, converted it to a path, moved the nodes to key locations, then fiddled with the control points to lay the splines along the perimeter:
Neck Cozy pattern – LB splines
Removing the bitmap makes the splines much more obvious and shows the much smoother perimeter:
Neck Cozy pattern – LB extended splines
Adding a few nodes to change the splined shape is much simpler than fiddling with the bitmap, particularly when tweaking their position as directed by someone who knows how the fabric will eventually take shape.
Add fiducial marks and a label, duplicate the shape, mirror it to get the other half, and fire the laser:
Neck Cozy pattern – as cut right
Fabric cutting isn’t in my wheelhouse, but I made the offer …
Mary is putting together a dogbone headrest pillow for a friend who will be spending a lot of time in a chair. It’ll be similar to this one from a while ago:
Dog Bone Pillow
She used Bonnie Browning’s pattern and I offered to laser-cut it as practice for other projects I have in mind.
It eventually worked out well enough:
Dog Bone Pillow – cut pattern
Fold a piece of fabric in half, align the pattern’s bottom edge with the fold, cut around the perimeter, make two more, and sew ’em together.
My first mistake was attempting to assemble the two halves of the pattern from the PDF document into a bitmap image using The GIMP:
D0G-BONE pattern – rejoined
That is both tedious and unnecessary, as I found out while trying to align the pieces.
The end goal is a simple and symmetric vector path defining the outline, including a line across the bottom, suitable for laser cutting. Rather than assembling an image, tracing it into a bunch of vectors, then cleaning up the mess, just lay a smooth spline vector path around half of it and invoke symmetry, much as happened with the Lip Balm Holder.
So import the slightly misaligned bitmap into LightBurn, draw a rectangle over just the left half, convert the rectangle to a path, then add a few nodes anchoring the splines to key points of the image:
Dog Bone Pillow – LB half pattern first splines
Although it’s not visible, the top and bottom spline nodes defining the vertical line down the middle are not quite vertically aligned, even though I dragged them to the middle of the pattern. Unsurprisingly, the bitmap image is not exactly aligned with the axes, even though the conversion from PDF to bitmap is entirely digital; the original design may be off by an itsy that would never matter for its intended application.
Tweak the splines / control points, add a few more nodes, and in short order the vector path runs pretty nearly along the middle of the bitmap image:
Dog Bone Pillow – LB half pattern overlay
Rather than trying to draw the second half just like the first half, duplicate the path and mirror the copy left-to-right to get the right half of the pattern. Grab the lower-left corner of the copy and snap it to the lower-right corner of the original, whereupon you will find the two points at the top of those lines don’t quite line up.
This is a grossly zoomed look at the top center, with the two red angles showing the two halves not quite meeting in the middle:
Click on the center point to define the Rotate center
Zoom way in on the top center
Click-n-drag the right corner to snap it onto the left corner
Done!
What just happened is that the right half now directly adjoins the left half, with the upper and lower center points overlapping.
Invoke the node editor and delete the center lines from both halves, leaving just the (overlaid) top and bottom nodes. Select both paths, then invoke Edit → Auto-join selected shapes to merge the two halves into one:
Dog Bone Pillow – LB splines
I missed the clip line in the middle of the top, but that’s why the first version is always a prototype.
This was easy, but it’s good to stay in practice …
The Smell of Molten Projects in the Morning 
