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.

Tag: Repairs

If it used to work, it can work again

Star Quilting Ruler Salvage: Laser Recutting

Mary picked up a pair of Star quilting rulers from the Quilting Guild’s “exchange” table:

Star quilting ruler – finished

They’re 1/4 inch laser-cut acrylic slabs dating back to the turn of the millennium, when laser cuttery wasn’t nearly as common as today. Apparently, the (now long gone) Gadget Girls had a problem with their laser: the larger star had eight of its ten lines not cut completely through the acrylic. The protective paper on the back had small perforations along a few of the lines, but nothing for most of them.

Well, I can fix that.

Lay the slab on the platform and lock it in place so it cannot move:

Star quilting ruler – laser setup

That’s with the original bottom side facing upward, so the laser beam will hit the uncut part of the lines.

Focus the laser atop some scrap 1/4 inch acrylic, then verify the red dot pointer is exactly concentric with the CO₂ beam by firing a test pulse, as in this punched card:

Red dot vs printed target vs laser spot alignment

Adjust as needed.

Jog the laser to put the red dot pointer exactly at a star point:

Star quilting ruler – laser point alignment

Hit Get Position in the Laser window so LightBurn knows where the laser head is located.

I’ve added the targets I normally use for LightBurn’s Print and Cut alignment to its Art Library, so I dragged one to the workspace, then hit Move to Laser Position to snap the target directly onto that point of the star.

Repeat for vertices along the star, then draw a multi-segment line = path between the target centers:

Star Ruler Re-cutting – LightBurn layout

That’s one continuous path from the upper right, counterclockwise around the star, ending in the center right. The missing pair of lines (and the vertex between them) were already cut, so I didn’t need to locate them.

The camera view shows the alignment, although IMO the camera simply isn’t capable of such finicky alignment:

Star Ruler Re-cutting – LightBurn layout overlay

As a confidence builder, I selected each target, moved the laser to that point, then fired a test pulse to verify the hole hit the vertex. In most cases, I couldn’t see the hole because it was within the original cut.

My 60 W laser can’t cut through 1/4 inch = 6 mm acrylic in a single pass, so I use a 10 mm/s @ 60% pass to get most of the way through and a 20 mm/s @ 60% pass to complete the cut. That seemed excessive for a mostly cut path, but a single 20 mm/s @ 60% pass didn’t completely clear the uncut sections.

So I used the normal two-pass cut and the star lifted right out:

Star quilting ruler – victory

Happy dance!

Although it is not obvious from the pictures, the star is not symmetric: it fits into the sheet in only one of its ten possible orientations. I will never know if that was a deliberate stylin’ decision or the result of hand layout before CAD spread throughout the land.

I managed to locate the vertices so accurately that the repeated cuts left edges indistinguishable from the original cuts on the two free sides, which was a pleasant surprise.

Mary promises to do something with those stars when she’s done with her current project(s). She may want the slab of acrylic around the large star trimmed into a smaller and more manageable decagon, in which case I will suddenly have a bounty of thick fluorescent green acrylic.

2026-03-26
Staedtler Mars Masterbow 551 02 WP: Assembly & Tweakage

The corners of Mary’s current quilt project need a 16 inch diameter circle, but my Drawer o’ Drawing Tools that should hold the trammel (distinct from trommel) point & pencil for a steel rule came up empty. While the TEC drawing kit has an extension leg for its compass, IMO it’s entirely too flexy for general use.

Further heap probes produced a Staedtler Mars Masterbow 551 02 WP compass with a robust extension leg:

Staedtler Masterbow – 551 02 WP assembled

It was likely a surplus deal and, to the best of my knowledge, has never been used, so that picture documents how the extension leg fits into the compass. It arrived with the lead in that compass leg, causing some confusion.

The key is to remove the point from that leg, insert the extension leg into the hole, then tighten the screw to clamp the leg in place:

Staedtler Masterbow – leg socket

The collet holding the point was either manufactured incorrectly (which I find hard to believe, because Staedtler in a package embossed “Western Germany”) or suffered damage along the way, as the only point fitting into it stuck out much too far:

Staedtler Masterbow – bow collet wrong point

The small container in the top picture held two spare leads and two other points:

Staedtler Masterbow – point assortment

It turns out the blunt end of the bottom point should fit into the collet, but I had to ream the collet jaws with a (hand-turned in a pin vise) 2.1 mm drill to let that happen:

Staedtler Masterbow – bow collet resized

Then everything lined up correctly and drawing could proceed, although the collet closer doesn’t (seem to) contribute anything to the proceedings.

The thumbscrew adjustment on the compass makes it much more rigid, even with the extension leg sticking out there for an 8 inch span.

I can (now) put the lead in the bow collet and the point in the compass, but IMO it’s easier to hold the compass while drawing around the circle. Your mileage, in the unlikely event you have one of these, may vary.

They definitely don’t make them like that any more …

2026-03-25
Magnetic Stirrer: Interior

Of late, the magnetic stirrer mixing my morning cocoa occasionally doesn’t start spinning when I turn it on, which calls for some investigation.

Removing the four obvious screws concealed under the rubber feet and prying off bottom cover reveals the trivial innards:

Magnetic stirrer – interior

The speed adjustment pot holds the little circuit board in place, with the green LED setting its jaunty angle.

The motor spins a pair of neodymium magnets:

Magnetic stirrer – magnet holder

I expected a gearbox instead of the direct drive setup.

Perhaps those whirling neodymium magnets have been slowly demagnetizing the motor’s internal (alnico?) magnets.

The motor brushes seem to be a pair of stiff wires, rather than carbon blocks, contacting the commutator, the wear from which may account for motor’s decreasing startup enthusiasm. Even though I didn’t expect a BLDC motor, this one may have been overly cheapnified.

Perhaps kickstarting the motor with the steel fork I use to fish the stirrer magnet out of the mug will get the thing going.

2026-03-23
Wobbly Clothes Rack Repair
A clothes rack Mary intended use with some work-in-progress quilts seemed entirely too wobbly for the purpose, so I tried tightening its screws. This did not go well, as some of the threaded inserts sunk into the vertical bars spun freely and, with a bit of persuasion, pulled straight out of their sockets:

Clothes rack screws – threaded insert penetrating oil

The reddish fluid is Kroil penetrating oil I hoped would free the screws from the corrosion locking them into the inserts. After an overnight soak, they still required force majeure:

Clothes rack screws – threaded insert in vise

The two inserts on the left came from the top of the rack and the other two from the bottom:

Clothes rack screws – threaded insert corrosion

Similar inserts have a hex drive recess and, because these are for 1/4-20 screws, I expected an inch size hex key. Nope, they want a hard metric 6 mm:

Clothes rack screws – threaded insert reformed

I cleaned up the corroded inserts by the simple expedient of tapping them firmly onto the 6 mm wrench held in the vise:

Clothes rack screws – threaded insert hex reforming

The crud around the bottom fell out of previous contestants during their reformation.

I considered epoxying the inserts in place, but settled for tucking a thick paper shim into each hole:

Clothes rack screws – threaded insert shim

They’re entirely snug right now and, should they work loose, I’ll coat the hole with epoxy, roll up another shim, screw the insert in place, await curing, then declare victory and hope nobody must ever remove them.

The 1/4-20 screws in the top member sit deep in recesses that surely had decorative wood plugs when the rack left the factory. Alas, they’re long gone, which may have let water / moisture corrode the screws + inserts . I’m not much good for “decorative” items, so this must suffice:

Clothes Rack Screw Covers – solid model

A snippet of double-sided tape on one side of the hole keeps them in place:

Clothes rack screws – cover installed

They look better in person …

The trivial OpenSCAD source code:
```
// Clothes rack screw cover
// Ed Nisley - KE4ZNU
// 2026-03-13

include <BOSL2/std.scad>

/* [Hidden] */

NumSides = 4*3*3*4;
$fn=NumSides;

//----------
// Build it
//  … with magic numbers from the rack

cyl(3.0,d=16.7,chamfer1=1.0,anchor=BOTTOM) position(TOP)
  cyl(6.0,d=12.9,chamfer2=1.0,anchor=BOTTOM);
```
2026-03-18
Monitor Arm Tilt Adjustment: Bad Part Repair

The tilt (it’s really “pitch”, but I can’t make a case for being that pedantic) adjustment on a recently arrived monitor stand / arm was nonfunctional, because the metal clamp had been bent about a millimeter too narrow to fit the plastic core. This is how it should look:

Monitor tilt adjustment – installed

As delivered, the plastic core was 32-ish mm wide and the gap at the base of the metal clamp was 31 mm, so the clamp arms stuck out at an angle on both ends of the core .

Because the cap screw bottomed out on the threads in the far side of the clamp, it couldn’t be tightened enough to force the clamp arms against the core.

Well, if the core is a millimeter too large for the clamp, shortening it should solve the problem; I can always shorten the screw if it comes to that.

Quick! To the mini-lathe:

Monitor tilt adjustment – lathe setup

Shaving half a millimeter from each side:

Monitor tilt adjustment – shaved

Twirling a deburring bit in each hole got rid of the swarf.

Rather than trimming the cap screw, a pair of fender washers keep it from bottoming out. With the core fitting into the clamp, the arms grip the core firmly on both sides with plenty of friction:

Monitor tilt adjustment – tweaked

I’ve bought this brand of arm before and the most recent pair have definitely been cheapnified from earlier ones. Because only one had a bad tilt clamp, the OEM may be in the middle of a changeover and shipped it with mismatched parts.

I wonder how many stands / arms get returned because they just don’t work?

2026-03-13
LED Garage Light: Autopsy

The hidden part of all three LED arrays in the dead garage light looked like this:

LED Garage Light – inadequate heatsink compound

Although the compound was still gooey, there wasn’t nearly enough of it. The few tendrils on the heatsink suggest the LED array had bowed upward, pulled away from the cast aluminum, and eliminated any direct conduction.

A bit of probing showed each LED array had 16 series groups of 4 parallel LEDS, with one group in each array failed open. That group was toward the end away from the inadequate heatsink compound: the LEDs died from heatstroke brought on by neglect.

The Drawer o’ LED Arrays disgorged a bag of surplus LEDs labeled “10 W 9-12 V 750 mA”:

LED Garage Light – epoxy replacement

It’s sitting on a generous blob of steel-filled JB Kwik epoxy that should do a great job of conducting heat. A bag of cheap constant-current supplies is on order.

Amazon has similar “10 W 9-12 V 350-450 mA” arrays.

Try as I might, I can’t get 10 W from those numbers, but I’ve never understood advertising math.

2026-03-10
Unbending Furnace Zone Drain Valve Knobs

For reasons long lost in our house’s history, two of the zone drain valves on the furnace apparently had something heavy fall on them from a great height:

Furnace zone drain valve – bashed knob

I was certain those knobs were made of brittle pot metal and would snap when I tried to un-bend them.

My weight bench being next to the furnace, I had plenty of opportunities to contemplate conjuring a 3D printed knob similar to the dumbbell nuts, but with the undamaged central part of the metal knob engaging the valve stem to avoid thermoplastic shapes around hot metal.

One can, of course, buy replacement knobs, but where’s the fun in that?

Expecting to cut most of the knob away, I applied needle-nose pliers to the rim and, mirabile dictu, not only did it not immediately snap, I managed to un-bend it into a reasonable facsimile of its original shape.

It wasn’t just beginner’s luck, because I did it again:

Furnace zone drain valve – unbent knobs

Both of those knobs have obvious fractures and aren’t the prettiest things you’ll ever see, but they don’t get a lot of use. I can say, without fear of contradiction, they’re in fine shape.

However, I’m certain those valves will need new washers if I ever turn those knobs …

2026-03-04