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

LED Light Switch: FAIL 2

Another switch for the temporary basement LED light strips failed the same way:

T8 LED power switch – failure 2

As always with such things, I suspect the only reason it has a UL mark on the back is because somebody else hasn’t missed theirs yet.

So I got a three-pack of inline switches with cute little indicator lights and set about replacing all of them:

Inline T8 power switch – internal

These switches carry absolutely no regulatory approval markings, although they do claim to carry 10 A at 250 V, which I take with another load of salt.

At least here in the US-of-A, a 240 VAC outlet has two “hot” wires carrying 120 VAC 180° out of phase, which means both conductors must be switched. Despite the voltage rating, only the L path goes through the clicky switch, with the N path along a strap just below the switch toggle. Using it on a 240 VAC circuit will kill you stone cold dead should you assume whatever it controls is turned off.

I secured the Line and Neutral conductors with crimp connectors, rather than just wrapping the 20 AWG wires around the screw terminals, because the case halves join without perimeter nesting: a bare millimeter of air in the gap between the halves separates the terminals from my fingers. A layer of good electrical tape on each side improved that situation, but not by much.

The complete lack of strain relief clamping on the cords prompted me to route the wires around the screw bosses. After a function check, squirts of hot melt glue anchored the two cords somewhat better.

Aaaaand I secured that loose strap on the right with an (identical to the others!) screw from the Tray o’ Random Screws. The other switches had both screws installed, so this one must have been a QC escape.

They suffice for the purpose, but … caveat emptor!

2024-07-02
Samsung Dishwasher: Upper Sprayer Disassembly

The Samsung dishwasher has an upper rack with a rotating sprayer that was thoroughly clogged with debris from its damaged screen filter:

Samsung dishwasher top nozzle – assembled

The whole assembly is readily available, although it seems any discrete part of the dishwasher costs about fifty bucks and this one wasn’t exactly broken.

It comes apart by rotating the lock ring (the one with right-angle ears sticking out on either side) 1/8 turn in the other direction from whichever way you think it should rotate. Hold the spray bar, shove the ears, and the spray arm will drop off:

Samsung dishwasher top nozzle – unlocked

The inside of the spray bar shows the locking details:

Samsung dishwasher top nozzle – sprayer

Now, here’s the tricky part.

The small ring under the locking ring, the one with two square nubbins pointing downward, snaps onto the pipe carrying the water. There’s a shallow notch around the pipe, the inside of the ring has a shallow lip, and the ring holds the whole affair onto the pipe.

Contrary to what I thought, the two nubbins do not latch onto anything. Apparently, they hold the ring in the proper position relative to the arm’s interior and that’s it.

The only way to reassemble the arm is to snap the small ring into place, with the lock ring above it, then install the arm and turn the lock ring 1/8 turn the other way. You (well, I) cannot snap the assembled arm into place, because the nubbins don’t provide enough oomph to seat the small ring on the pipe.

Unless I write that down, I will never remember it …

Protip: Needle nose tweezers are invaluable for picking crud out of the nozzles. Iterate on picking and flushing with water until nothing more comes out, then expect to repeat the process several times as more crud emerges from the depths of the plumbing.

Although it is apparently possible to disassemble the spray arm by unlatching all the snaps along the edge, I’d reserve that for a moment when lives depended on unclogging the nozzles.

2024-06-27
Antique Desk Chair: Leg Rebuild

With the seat glued and the old caster sockets yanked, I carved a piece of plywood to fit the gap in one leg:

Wood desk chair – leg filler – bottom

After whittling the wood to kinda-sorta go in there, I pressed it against snippets of carbon paper (remember carbon paper?) to mark the contact points and carve them off:

Wood desk chair – leg filler – carbon paper fitting

This occupied most of a SquidWrench remote meeting, but eventually sank it flush with the leg:

Wood desk chair – leg filler – side

Now, that’s not the prettiest job you’ve ever seen, but it gets worse:

Wood desk chair – leg epoxy shaping

This time around, I tinted the epoxy with brown and black dye, which knocked the color back to something tolerable and increased the curing time well beyond the usual couple of hours. Fortunately, I wasn’t in a hurry and it was pretty much done by the next afternoon.

Whereupon I mixed up another bodacious batch of epoxy:

Wood desk chair – caster pin prep

The Kapton tape wrap kept (most of) the epoxy out of the end of the sockets. I buttered up the sockets just below their serrated heads and tapped them into the legs:

Wood desk chair – caster pin installed

Yeah, I wiped that down a little better before another overnight cure left the four pins firmly secured in their legs; the pins still rotate (albeit stiffly) in the sockets, although the casters really swivel on their pins.

A cast iron fitting of the kind they just don’t make any more holds the legs in place:

Wood desk chair – bottom plate

My screw collection lacks chonky wood screws, but I doubt anybody will ever notice that shiny crosspoint screw.

In any event, the plate holds the legs in tapered slots along the cast iron base that also guides the height adjusting leadscrew under the seat:

Wood desk chair – leg wedge shims

The wood dovetails in the legs were a bit worn / shrunken, so I shimmed them with two strips of 3.5 mil = 0.09 mm stainless steel tape on each side and tapped the legs into place with a plastic mallet. The steel is completely invisible from outside and the legs are magically solid, just like they should be.

As expected, the new casters clash horribly with the chair’s classic style:

Wood desk chair – repaired

Somewhat to my surprise, it’s now undergoing a field test at Mary’s desk, where it replaces a chair she never liked. The seat adjusts down enough to let her feet reach the floor (which most modern chairs do not) and the edge doesn’t press on the back of her legs. We fiddled with the backrest height / angle / tension and it feels surprisingly good.

You gotta admire something with that kind of durability and repairability.

A good refinishing job would definitely improve its appearance, but that’s well beyond my abilities.

2024-06-25
Samsung Dishwasher Screen Filter Fix

The Screen Filter (DD81-02011A) in our Samsung dishwasher (DW80K7050US) turned out to have a mold defect from the factory that’s been sitting there since the previous owners had it installed back in 2018:

Samsung dishwasher screen filter – gap

The mesh apparently didn’t quite make it into the molded plastic, so that little gap has been letting debris in the wash water circulate through the spray bars and clog the orifices.

While replacements are readily available, they seem rather pricey for what they are and this seemed like an easy repair:

Samsung dishwasher screen filter – glued

That’s a bead of EVA hot melt glue that will probably withstand the 163 °F = 73 °C “sanitize” cycle we haven’t had any occasion to use and seems no more toxic than anything else around here.

Protip: if your dishwasher has a filter, it’s likely clogged with a nasty accumulation of gunk, too …

2024-06-24
Antique Desk Chair Woodwork

A wood desk chair that I’ve known since I was a pup finally got some much-needed attention, although not a restoration. By and large, I’m finally sorting out that corner of the basement and needed to put the chair’s parts back together so I can work on something else.

The wood seat consists of several slabs glued along keyed joints, one of which had fractured into a rough mess. Amazingly, the two sides fit perfectly together, albeit with the bottom no longer a planar surface, and glued up just like they should:

Wood desk chair – seat clamping

The chair isn’t up to contemporary office standards, but it has a seat elevation screw, a backrest with adjustable angle & elevation, and even a backrest tension setting:

Wood desk chair – ironwork

It was the cutting edge of desk chair technology:

Wood desk chair – patented

I vaguely recall it rolled on long-vanished steel-wheeled casters. Somewhat less long ago, one of the legs broke enough to lose its caster socket (about which, more later), so I set about yanking the three remaining sockets:

Wood desk chair – caster socket removal

During that struggle, another leg revealed a neat woodwork joint:

Wood desk chair – leg joint

It’s easy to remove a caster socket when you can bash it from the top!

Gluing that piece back in place required Too Many Clamps™ aligning it with the leg:

Wood desk chair – leg clamping

But the end result looks pretty good:

Wood desk chair – leg glued

They did a nice job of matching the wood grain; I hadn’t noticed that joint while attacking the socket.

Pending restoring the broken leg’s socket, the soon-to-arrive new casters will clash horribly with the chair’s woodwork. At least it’ll roll again and its new plastic wheels won’t scar the floors.

2024-06-19
Folding Wood Chair Arm Repair

One of the folding wood chairs that Came With The House™ had a loose arm that turned out to be due to a missing chunk of wood:

Wood chair arm – as found

The obvious lay of the grain shows why it failed like that, surely hastened by the crack below the screw.

So I cut a snippet of brass tubing that, mirabile dictu, fit both the hole and the M6 screw, mixed up some wood epoxy and buttered it up:

Wood chair arm – brass tube epoxy fill

The crack extended entirely through the arm and was more extensive that seemed reasonable to expect the epoxy to handle on its own:

Wood chair arm – splits

So I ~~slobbered~~ ~~soaked~~ saturated the cracks with wood hardener and clamped them shut:

Wood chair arm – clamping

The hardener is intended to solidify rotted wood, but it makes a reasonable adhesive and, being much more liquid than ordinary wood glues, seemed like it would penetrate further into the cracks than anything else on hand. We shall see how this works out.

Rummaging in the Drawer o’ M6 Screws produced a better match to the brass tube than the original flat head screw:

Wood chair arm – repaired

It screws into a fancy tee nut in the upright chair rail, where a dot of thread locker should hold it forevermore.

I hit the exposed end with some sandpaper to smooth off the last of those smears and, after a few years, it’ll probably look like it grew there.

2024-06-07
Laser Cutter: Fourth Corner Adjustment

The pieces of a larger scrap bin ventured into the right-front quarter of the laser platform and didn’t cut well at all:

Fourth Corner beam misalignment – 2024-05-31

A closer look at the bottom right corner of that image shows the problem in more detail:

Fourth Corner beam misalignment – detail – 2024-05-31

The intended cuts are the dark lines, each with a poorly defined scorch 2 mm on its left. Knowing that the nozzle is about 4 mm, this suggests the beam is off-center enough to juuuust kiss the nozzle and splash the outer part of the beam away.

Having recently spot-checked the alignment and not seen any odd behavior on another platform-spanning project, this was puzzling. Given that the laser recently survived a move from one Basement Shop to another, with plenty of jostling while standing on end, I suppose I should have been more careful.

The biggest clue was seeing the shadow lines only near the front-right corner and noting they got worse farther into the corner. This seemed like the “fourth-corner” alignment problem described by St. Sadler some years ago and covered in a more succinct recent video.

AFAICT, the problem boils down to the difficulty of precisely aligning the beam at the longest distance it travels in the front-right corner. Careful adjustment of Mirror 1, after getting everything else lined up properly, seems to be solution.

The initial alignment at the first two mirrors looks OK, using targets taped parallel to the mirror plane:

Beam Alignment – Initial M1 M2 – 2024-05-31

The beam is slightly off-center at Mirror 1 and only a millimeter high on Mirror 2 at either end of the gantry travel along the Y axis.

The beam position at the laser head entry upstream of Mirror 3 shows the problem:

Beam Alignment – Initial M3 entry – 2024-05-31

The targets are left- and right-rear, left- and right-front, with varying pulse lengths obviously underpowering the last and most distant shot.

Looks like a classic fourth-corner problem!

Tweaking Mirror 1 by about 1/8 turn of the adjusting screw to angle the beam vertically upward eventually put the beam dead-center at Mirror 3:

Beam Alignment – M3 adjustments – 2024-05-31

The bottom two targets are double pulses at the left- & right-rear and ‑front, so the beam is now well-centered.

A quick cross-check shows the beam remains centered on Mirror 2 at the front- and rear-end of the gantry travel, Mirror 3 is still OK, and the beam comes out of the center of the nozzle aperture:

Beam Alignment – M2 M3 exit final – 2024-05-31

Subsequent cutting proceeded perfectly all over the platform, so I think the alignment is now as good as it gets or, perhaps, as good as it needs to be.

Whew!

2024-06-05