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.

Category: Machine Shop

Mechanical widgetry

Frosted Snowflakes

After the first two snowflake coasters, it finally penetrated my thick skill that putting a 1 mm hole in the flake cut from the center of the plywood would convert it into a decorative window hanging:

Snowflake Hanger – plywood

Admittedly, I may be using the word “decorative” in a manner you had not previously encountered, but work with me on this.

Cutting a similar flake from transparent acrylic looks better:

Snowflake Hanger – blue acrylic

Transparent acrylic turned out to be, well, too transparent, so I set up a LightBurn layout to “engrave” a light frosting on the flake before cutting it out:

Snowflake Hangers – engraving in situ

That worked for all subsequent flakes, but I had to do something about the first few flakes. After realizing that the time to engrave an object depends only on its width, I set up a rectangle with the proper parameters, snugged two forlorn flakes next to each other, and fired the laser:

Snowflake Hangers – retroactive engraving

I thought using cardboard was a Good Idea™ for a stable backing, but lightly vaporizing the top layer produced an unbelievable amount of filth:

Snowflake Hangers – frosted

I had to scrub those poor flakes with dish detergent and a toothbrush to get them even close to their former pristine state; the blue one may never recover.

Anyhow, frosted flakes look good if you don’t look closely:

Snowflake Hangers – frosted

The grid pattern comes from the window screen in direct sunlight; the vertical bars are DIY BirdSavers.

The LightBurn layout produces 120 mm coasters to fit my 20 ounce mugs:

Snowflake Coaster 120 mm – LB Layout

You get two hanging flakes: one plain plywood and one frosted acrylic!

The LightBurn SVG layout as a GitHub Gist:

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2023-01-06
Snowflake Coasters: Kerf Compensation

A flurry of snowflake coasters:

Snowflake Coaster – assortment

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.

2023-01-05
Ersatz Library Card

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 rear surface data is engraved directly into the same Trolase laminated acrylic I used for the plant tags:

Library card tags – rear

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.

2023-01-04
Sears / Kenmore Vacuum: Design Tweakage

Despite cogent reasons for not buying another Sears vacuum cleaner, the brand currently represents a local maximum of the desirability curve: cheap, readily available, works well enough, and, surprisingly, bags for the defunct Progressive (whatever that meant) vacuum seem to fit just fine.

But the new one does come with some annoyances, starting with trendy dark gray engraved / molded control markings:

Sears Vacuum – power and cord controls

Quick: from the other end of the vacuum hose, which one must you stomp to turn it off?

Well, I can fix that:

Sears Vacuum – marked power switch

After the Progressive’s bizarre and overly complex tool fittings, the new unit has tools that slip-fit onto a classic steel tube, which means I can throw all those adapters into a box of 3D printing examples for use in the unlikely event I ever do another show-n-tell presentation.

It also has a simple rotating suction control ring at the handle:

Sears Vacuum – marked suction vent control

Which, as you can tell from the fluorescent tape, featured the same embossed and unreadably small dark gray markings.

Because that ring and its glaring tape is invisible from the user’s end of the handle, I eventually duct-taped the ring in position to prevent another inadvertent loss-of-suction accident.

If we ever need reduced suction on a regular basis, I’ll conjure a better ring from the vasty digital deep:

Sears Vacuum – suction vent doodle

I obviously no longer form deep emotional attachments to these things …

2023-01-03
Kitchen Knife Handle: Epoxy Patch

The black plastic-like substance molded around the tang of our daily driver kitchen knife crumbled away near the blade and eventually reached the point my thumb couldn’t stand it any more. Given the good results of the JB Weld coating on the cheese slicer (which is still going strong after four years), I chipped away the loose fragments on all sides, wire-brushed the crater with alcohol, and filled it with epoxy:

Kitchen knife handle – tape reforming

The Kapton tape bridges the solid part of the handle with the metal just behind the blade, holding the epoxy in more-or-less the right shape while it cured overnight. The other side looks much the same, which is why I couldn’t just let it sit out.

A few minutes with a file and wire wheel knocked back the high spots and left it looking much better than before, if a bit scuffed:

Kitchen knife handle – restored

The tang inside the molded shell is kinda-sorta cruciform, with an exposed rib along both sides. I think the plastic shrank around the tang in that gap between the ribs and the blade, where its lack of flexibility caused the cracks.

Neither a beautiful restoration nor a permanent fix, but it ought to last for a while. Similar cracks at the hilt end of the handle suggest more repairs lie in its future.

2022-12-30
Seasonal Snowflake Coasters
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
- Ungroup to separate the flake’s strokes
- Weld the strokes together to remove the overlaps
- Wrap a coaster outline around it
- Resize the flake as needed
- Set layer parameters as needed
- Duplicate the flake
- Embiggen as needed
- Unleash the laser!
The LightBurn SVG layout as a GitHub Gist:

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2022-12-29
Seasonal Holly Coasters

Starting with a random SVG holly image from the InterTubes:

Holly Coaster – assortment

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.

The LightBurn SVG layout as a GitHub Gist:

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2022-12-28