Glass vs. Epoxy: Divot!

The WS2812 RGB LED atop the Bowl of Fire Floodlight

Reflector floodlight - purple phase

Reflector floodlight – purple phase

failed in the usual way after a bit over a year of constant use.

I’d done an unusually good job of epoxying the ersatz heatsink in place:

Reflector floodlight - finned LED holder

Reflector floodlight – finned LED holder

I wrapped the bulb in a towel with only the heatsink sticking out, whacked the side of the heatsink parallel to the glass with a plastic-face hammer, and it popped right off:

Epoxy vs glass - divot

Epoxy vs glass – divot

The missing piece of the epoxy ring turned out to be a divot ripped out of the glass, which I didn’t notice until I’d chipped the fragment off the aluminum, so no pictures.

Given the relative strengths of epoxy and glass, pulling a divot seems impossible, but folks doing 3D printing on glass platforms have been reporting exactly that failure for years. The prevailing theory seems to involve small scratches and defects in the glass surface, with subsequent weakening, and stresses applied to the epoxy perpendicular to the glass surface pulling the cracks apart.

Replacing the RGB LED will require drilling it out and probably a complete rewiring, because I seem to have made liberal use of epoxy inside the heatsink and brass tube.




Pure Matte Black the Hard Way

The best way to get a pure, non-reflective black uses optics, not pigments:

Matte black blade edges

Matte black blade edges

The shiny steel blades reflect light just fine, but the reflections have no way back out of the gap between adjacent edges: the angle of reflection always points away from you and the incoming light.

I always admire the blackness when I open that box.

Yes, I’m a member of the Society of the Easily Amused.


Sunglass Earpiece Trimming

Mary doesn’t like wearing the wrap-around-her-head earpieces found on sunglasses these days under her bicycle helmet, so I must trim them to fit:

Sunglass earpiece trim

Sunglass earpiece trim

Perhaps I won’t need an old pair to prepare the next set: a scant four inches from the hinge.

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Amateur Lock Picking

For reasons not relevant here, I was called upon to open a bulletin-board lock with a complete lack of keys:

Bulletin Board Lock - locked

Bulletin Board Lock – locked

It’s obviously not the highest security lock you’ve ever seen. Armed with a small screwdriver and an old darning needle, this took the better part of 30 seconds:

Bulletin Board Lock - opened

Bulletin Board Lock – opened

Actually, I devoted a few minutes to verify none of my collection of random keys would suffice.

Replacing the lock not being within my remit, I improvised a simple retainer from available materials:

Bulletin Board Lock - improvised strap retainer - front

Bulletin Board Lock – improvised strap retainer – front

Yes, the nylon cable tie will surely pull out of the latch:

Bulletin Board Lock - improvised strap retainer

Bulletin Board Lock – improvised strap retainer

And I admit the installation’s security has taken a definite downward step:

Bulletin Board Lock - push pin security

Bulletin Board Lock – push pin security

Some day, I’ll tote a wrench to the site, remove the lock, and improve the improvisation.

Replacing the lock seems mired in an intractable budgetary wrangle. Similar locks being five bucks on Amazon, I’m tempted to just make it happen, but doing so would apparently roil the decision-making stratum. I’m perfectly happy to remain an on-call techie devoid of political ambition.

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Cheese Slicer: XTC-3D Epoxy Coating

We have, as you might expect, a Favorite Cheese Slicer of no particular provenance. Being made of cheap pot metal, it left black smudges wherever it went and, decades ago, I coated it with bright red rubbery grip material. Recently, the coating became lumpy and peeling off the loose sections revealed a definite problem:

Cheese slicer - aluminum corrosion

Cheese slicer – aluminum corrosion

Vigorous scrubbing with a foam sanding block and a Scotchbrite pad, interspersed with rotary wire brushing, removed the corrosion and left a slightly pitted metal frame. Protip: scrub under water and wire-brush with a vacuum hose to keep the dust under control.

A pair of 6-32 screws, nuts, and brass sleeves, with two oil dots protecting the frame threads, provided hand grips while I wiped it down with denatured alcohol and coated it with XTC-3D epoxy:

Cheese slicer - epoxy curing

Cheese slicer – epoxy curing

Turns out the mixing stick worked quite well to cover the entire thing, as the epoxy does a great job of leveling itself. I suppose wasting a tiny brush would be more professional, but …

It quietly dripped excess epoxy into a strategically placed trash can for about ten minutes. I wiped off the final drip before the epoxy solidified, leaving a smooth layer over the end of the handle:

Cheese slicer - reassembled

Cheese slicer – reassembled

It’s back in service and works as well as ever, with a handle now smooth to the touch. I suppose I could have tinted the epoxy to hide the metal, but we regard those corrosion pits as beausage.

I’ve slathered XTC-3D on some 3D printed parts, but have no idea how durable it is; this should serve as an accelerated survival test under rather harsh usage.

The instruction sheet says XTC-3D isn’t the most transparent epoxy they make and, indeed, the layer left in the mixing pan came out more hazy than I expected:

XTC-3D Epoxy - thin cured layer

XTC-3D Epoxy – thin cured layer

They point out the haze doesn’t matter for thin surface coatings, which is certainly true.


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Whirlpool Refrigerator Drawer Slide: Another Bracket

Thirteen years after the original repair on the left side and eight years after I fixed the drawer slide on the right side, this happened:

Refrigerator shelf slide - failed parts

Refrigerator shelf slide – failed parts

The general idea is to wrap a new bracket around the old bracket, because trying to remove the old one will probably cause more damage:

Refrigerator shelf slide - trial assembly

Refrigerator shelf slide – trial assembly

A pair of screws hold the new bracket to the shelf support:

Refrigerator shelf slide - support screw nut openings

Refrigerator shelf slide – support screw nut openings

Those two screws must support the entire weight of the drawer, which is exactly what broke the original all-plastic frame and slide.

The epoxy chip and transparent plastic sheet in the first picture spaced the old aluminum bracket away from the shelf support and reduced the space beyond the new bracket enough to require drilling access holes. Fortunately, they’re hidden inside the support frame, so nobody will ever know.

The shelf support is a huge floppy rectangle, so I clamped it to the bench vise while drilling the holes:

Refrigerator shelf slide - upright vise clamp

Refrigerator shelf slide – upright vise clamp

The new bracket is on the right, with a sheet of white acrylic spacing it away from the shelf support by exactly the same distance as the angled aluminum snippet replacing the failed epoxy & plastic on the broken part:

Refrigerator shelf slide - bracket parts

Refrigerator shelf slide – bracket parts

The two holes in the middle of the aluminum parts show that I used exactly the same angle brackets as raw material. It’ll be a sad day when I eventually use the last of those brackets.

Putting the parts together, with double-stick tape holding all the parts in place, shows how they fit:

Refrigerator shelf slide - repair trial assembly

Refrigerator shelf slide – repair trial assembly

And then it just snapped into place. I didn’t bother pretending solvent glue would help anything, nor did I apply any epoxy, so this whole thing hangs from those two 4-40 screws. On the other paw, their steel beats the original white plastic.

I devoutly hope to never rebuild the actual drawer slide, but these dimensions may help somebody else out of a jam:

Refrigerator shelf slide - dimensions

Refrigerator shelf slide – dimensions

The vertical “40” dimension refers to the available space from the bottom of the white plastic part to the top of the shelf support frame; the new bracket is a tad shorter than that.

The plastic parts in that refrigerator have been a complete disappointment: were it not for my relentless repair jones, we’d likely be on our third or fourth refrigerator by now. Oddly, the cooling parts continue to chug along (*), without more than the occasional loud noise in the middle of the night.

We’re definitely doing our part to reduce our waste stream.

(*) The most recent freezer fan hasn’t failed yet!



Hydrant Wrench

Just because I can:

Fire Hydrant Wrench

Fire Hydrant Wrench

The Slic3r preview shows a bit more detail:

Hydrant Wrench - Slic3r preview

Hydrant Wrench – Slic3r preview

Even an inch-thick handle wouldn’t have enough mojo for the task.

Wikipedia has the equations you need to go from the easily measured “height” (vertex to opposite side) dimension to the pentagon’s “outside radius”, which equals the radius of the circumscribed circle needed by OpenSCAD.

The OpenSCAD source code as a GitHub Gist:

Sorry ’bout that … had to do it.