Bobbin Rock

Mary handed me a bobbin with a trouble report: it fit into the bobbin holder either way, but would go into the sewing machine either poorly or not at all.

Based on past experience with this lot of bobbins (*), I expected to find a burr inside the steel hub left behind by the saw cut creating the drive dog slot, so this came as a surprise:

Bobbin Rock - overview
Bobbin Rock – overview

A closer look:

Bobbin Rock - detail
Bobbin Rock – detail

That pebble was jammed in place so firmly I needed a pin punch: a small screwdriver wasn’t enough.

It came new from the factory like that, which makes one wonder just exactly what the factory floor looks like.

More likely, the bobbins spend their last few hours in a vibratory polisher and that little rock just crept with all the walnut shell kibble.

Works fine now, so we’ll call it a win.

(*) I gave her a lot of 100 to ensure she never had to unload a bobbin to keep her new Juki well-fed.

Eyeglass Spring Temple: Screw Hole Tweak

A screws in one of Mary’s eyeglasses unscrewed itself, but, miraculously, we found it and I retired to the shop.

Because the glasses have spring temples, the screw would not align no matter what force I applied to it:

Eyeglass spring temple - screw misalignment
Eyeglass spring temple – screw misalignment

So I just embiggened the hole until the available force did the trick:

Eyeglass spring temple - hole filing
Eyeglass spring temple – hole filing

Dots of Loctite worked into the threads should prevent that from happening again, but I’ve learned to never say never.

In retrospect, the temple pivots have an exposed slot that I think would allow jamming a block in place after pulling the spring-loaded pivot outward. Temple springs are impossibly stiff and I have previously failed to budge them in glasses without the slots, so I don’t know how well that might work.

Verily: If brute force isn’t working for you, then you’re not using enough of it.

Kitchen Under-sink Cabinet Fan Incident

During the course of diagnosing and fixing the latest oven igniter failure, an unrelated series of events produced a flood under the kitchen sink and across the floor. After cleaning up the mess and determining the floor under the cabinet was merely damp, rather than wet, I drilled a hole suitable for another PC cooling fan from the Box o’ MostlyFans, installed the fan to pull air upward, and let it run for a couple of days while watching the humidity drop.

Fortunately, I had a hole saw exactly the right size for an 80 mm case fan:

Kitchen sink - fan cover plate
Kitchen sink – fan cover plate

I will lay big money on a bet saying your kitchen cabinets don’t have Real Wood like that, nor are the interiors painted bold Chinese Red. This place really is a time capsule from 1955.

While the drying happened, I made a hole cover from 1.5 mm black acrylic and, there being no style points involved, rounded up a quartet of black-oxide self-drilling sheet metal screws to hold it in place.

Although it’s not obvious, there’s a layer of transparent plastic “shelf paper” in there. It covers the fan hole under the cover, so any future spills will have approximately the same difficulty reaching the floor as this one did.

The LightBurn layout produces both the fan cover and a template to mark the four screw holes around the fan opening:

Kitchen Sink Fan - LB layout
Kitchen Sink Fan – LB layout

The blue tool layer lines serve as a guide for the rest of the cover layout; the matching orange square on the right marks the fan outline on the drill template as a quick size check.

No need for an SVG version, because now that you have the general idea, it’s easy to recreate it for your own fan.

Kenmore 362.75581890 Oven: Another Igniter Bites The Dust

Our story so far:

  • We installed a Kenmore gas range around the turn of the millennium
  • 2006 – Oven burner tube & igniter replaced
  • 2014 – Igniter replaced

Apparently igniters last about eight years, regardless of provenance, because the igniter just failed, with the usual symptoms of low current draw (about 2 A), failed ignition, and a faint smell of propane (well, mercaptan) before the safety valve kicked in:

Oven igniter - location
Oven igniter – location

The new igniter, another low-buck Amazon offering, came with half a green plastic connector block that mated neatly with the existing half under the oven. Unfortunately, the new wires had female pins crimped on their ends, rather than the male pins required by the existing connector and the ceramic wire nuts I’d used to join the previous igniter to the OEM connector were non-removable.

So I trimmed the old wires to a usable length and applied the new ceramic wire nuts to the stubs:

Oven igniter - connector rewiring
Oven igniter – connector rewiring

Also as before, the new igniter measures 3 A, definitely below the low end of the valve’s 3.3 to 3.6 A range:

Oven igniter - current test
Oven igniter – current test

If this one lasts eight years, I won’t be the guy replacing it …

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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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
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
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
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
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
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
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
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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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.