Shoulder PT Pulley: Last 10% Manufacturing

Mary’s PT requires a Shoulder Pulley, so I got one that seemed better constructed than the cheapest Amazon crap. In particular, this view suggested the pulley ran on a bearing:

Slim Panda Shoulder Pulley - detail view
Slim Panda Shoulder Pulley – detail view

Which turned out to be the case, but, also as expected, the whole thing required a bit of finishing before being put in service.

It’s intended to hang from a strap trapped between an interior door and its frame. The strap was intended to attach to the block (a.k.a. “Thickened base”) through a breathtakingly awkward pair of low-end carabiners:

Slim Panda Shoulder Pulley - carabiners
Slim Panda Shoulder Pulley – carabiners

Which I immediately replaced with a simple, silent, sufficiently strong black nylon cable tie:

Shoulder PT Pulley - block hardware
Shoulder PT Pulley – block hardware

Rather than let the metal block clunk against the door, it now sports a pair of cork-surfaced bumper plates:

Shoulder PT Pulley - side plates installed
Shoulder PT Pulley – side plates installed

A doodle of the block dimensions:

Shoulder Pulley - dimension doodle
Shoulder Pulley – dimension doodle

Which turned into a simple LightBurn layout:

Shoulder PT Pulley Side Plates - LB layout
Shoulder PT Pulley Side Plates – LB layout

The blue construction lines represent the actual block & pulley, with the red cut lines offset 2 mm to the outside to ensure the metal stays within the bumpers. It’s possible to pick the block up and whack the pulley against the door, so don’t do that.

Cut out two pieces of 3 mm MDF, two pieces from a cork coaster (covered with blue tape and cut with the paper backing up), peel-n-stick the cork to the MDF, put double-sided foam tape on the block, peel-n-stick the bumpers, then hang on the attic door.

Now it works the way it should!

The LightBurn SVG layout as a GitHub Gist:

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Ersatz Library Card: Fixed

Sharper eyes than mine pointed out I misspelled Poughkeepsie, so I took advantage of the opportunity to make the whole thing look better:

Library card tag - revised front
Library card tag – revised front

It turns out the low-surface-energy tape stuck like glue to the acrylic tag (because that’s what it’s designed for) and peeled right off the laminating film on the printed paper. So I stuck some ordinary adhesive film to the back of the new paper label, left its protective paper on the other side, cold laminated the film+paper, laser-cut the outline, peeled off the back side of the laminating film with the protective paper, and stuck the new adhesive to the LSE tape still on the tag.

I have no idea how well this will work out in the long term, what with two adhesive layers bonded to each other, but this whole thing is in the nature of an experiment.

Holly Coaster: Improved Mirror Setup

Other than demonstrating that it’s possible to laser-engrave a 3 mm deep pocket in a ¼ inch thick piece of scrap paneling, the process didn’t have much to recommend it:

Holly Coaster - mirror flaws
Holly Coaster – mirror flaws

So I re-did the layout to put the 3 mm mirror in 3 mm thick plywood:

Holly Coaster - overview
Holly Coaster – overview

The coaster has a self-adhesive cork pad on the bottom, which required an intermediate adhesive layer holding the aluminized Mylar reflector on the bottom of the mirror to brighten the colored areas.

The LightBurn layout shows all the pieces:

Holly Mirror Coaster - LB layout
Holly Mirror Coaster – LB layout

The plywood cuts with the good side down, although “good” is certainly a judgement call with B/BB grade plywood. I cover the good side with blue painter’s tape to reduce scorch marks. In a real application, you’d do some sanding and finishing, probably before cutting; in this case, I want to see what happens to bare wood in coaster duty.

Engrave and cut the mirror with the backing upward:

Holly Coaster - removing mirror layer
Holly Coaster – removing mirror layer

The tracer rounds may be burning aluminum.

I colored the engraved areas with fat-tip permanent markers, despite knowing the alcohol will crack the acrylic. In real life, you’d use spray paint, probably with laser-cut tape masks.

The adhesive layer extends 2 mm beyond the mirror perimeter to stick onto the bottom face of the plywood:

Holly Coaster - adhesive placement
Holly Coaster – adhesive placement

Peeling off the paper reveals the adhesive tape stuck to the back side of the mirror:

Holly Coaster - adhesive exposed
Holly Coaster – adhesive exposed

Apply the similarly embiggened aluminized Mylar to the adhesive:

Holly Coaster - mylar placed
Holly Coaster – mylar placed

Cutting the holly shape directly from the original foot-square adhesive sheet lets me tuck smaller shapes into the remaining uncut areas. In a production environment, however, joining the Mylar and adhesive (perhaps using pre-cut squares), then cutting them as one sheet would definitely simplify the process.

Then peel-n-stick a cork disk (thus explaining why the plywood is exactly 4 inch OD) on the bottom:

Holly Coaster - edge view
Holly Coaster – edge view

I’ve been aligning the cork by feel, which explains the half-millimeter overhang along the right side. Inexplicably, I have yet to justify an alignment fixture.

The LightBurn SVG layout as a GitHub Gist:

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Snowflake Coasters: Kerf Compensation

A flurry of snowflake coasters:

Snowflake Coaster - assortment
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
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
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.

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
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
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
Library card tags – rear

The smaller text uses dot mode and the bars & number are engraved:

Library card tag - detail
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.

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
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
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
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
Sears Vacuum – suction vent doodle

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

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
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
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
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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