Archive for category Machine Shop

Pot Lid Repair

For reasons not relevant here, we (temporarily) have a set of pots with glass lids. One of lids had a remarkable amount of crud between the glass and the trim ring under the knob, which turned out to be corrosion falling off the screw. Trying to remove the screw produced the expected result:

CKC Pot Lid - broken screw in handle

CKC Pot Lid – broken screw in handle

For whatever reason, they used an ordinary, not stainless, steel screw:

CKC Pot Lid - corroded screw

CKC Pot Lid – corroded screw

I figured I could mill the stub flat, drill out the remainder, install a new insert, and be done with it. The knob has a convex surface and, even though this looked stupid, I tried clamping it atop a wood pad:

CKC Pot Lid - precarious clamping

CKC Pot Lid – precarious clamping

Two gentle cutter passes convinced me it was, in fact, a lethally stupid setup.

Soooo, I poured some ShapeLock pellets into a defunct (and very small) loaf pan, melted them in near-boiling water, and pressed the knob into the middle, atop some stretchy film to prevent gluing the knob in place:

CKC Pot Lid - ShapeLock bedding

CKC Pot Lid – ShapeLock bedding

That’s eyeballometrically level, which is good enough, and the knob sits mechanically locked into the room-temperature plastic slab. Clamping everything down again makes for a much more secure operation:

CKC Pot Lid - clamped ShapeLock fixture

CKC Pot Lid – clamped ShapeLock fixture

A few minutes of manual milling exposes the original brass insert molded into the knob, with the steel screw firmly corroded in the middle:

CKC Pot Lid - screw stub milled flat

CKC Pot Lid – screw stub milled flat

Center-drill, drill small-medium-large, and eventually the entire insert vanishes in  a maelstrom of chips and dust:

CKC Pot Lid - OEM insert removed

CKC Pot Lid – OEM insert removed

Run a 10-32 stud into an insert, grab in drill chuck, dab JB Kwik around the knurls, press in place while everything’s still aligned in the Sherline, pause for curing, re-melt the ShapeLock, and the insert looks like it grew there:

CKC Pot Lid - new insert installed

CKC Pot Lid – new insert installed

Wonder to tell, a 1 inch 10-32 screw fit perfectly through the pot lid into the knob, with a dab of low-strength Loctite securing it. Reassemble everything in reverse order, and it’s all good:

CKC Pot Lid - repaired knob

CKC Pot Lid – repaired knob

Well, apart from those cracks. I decided I will not borrow trouble from the future: we’ll let those problems surface on their own and, if I’m still in the loop, I can fix them.


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Kenmore 158 Sewing Machine: Another Foot Pedal Rebuild

The pedal on Mary’s most recent Kenmore 158 lost its low-speed control, which meant I must add a few more graphite / carbon disks to the stacks:

Kenmore 158 - carbon disks

Kenmore 158 – carbon disks

The contacts needed a bit of attention, too:

Kenmore 158 - carbon contact plates - detail

Kenmore 158 – carbon contact plates – detail

Contrary to what I found in the previous rheostats, these stacks end with a double-thick graphite disk backed up by a disk of brass shimstock, all of which needed cleaning, too. No broken disks, none severely eroded, no debris, just a general shortening of the stacks; I think the disks gradually turn into carbon dioxide.

Each stack has 42 graphite disks that average 0.79 mm thick, the double-thick disks measure 1.5 mm, and the brass shims are 0.30 mm = 12 mil. The punched contacts on those brass plates stand 0.95 mm proud of the surface.

With the big graphite plugs in place, the ceramic housing had 37 mm deep holes for the disk stacks. Subtracting the 0.95 mm contact leaves about 36 mm and, seeing as how the stacks add up to just under 36 mm overall, there’s barely room for one additional disk. I added one to each stack, buttoned the pedal up, and it works perfectly again.

Good thing I have a bag of those disks from the crash test dummy machine!



USB Gooseneck Extension Innards

The bandsaw needs more light on the blade, but a fixed lamp will certainly get in the way of something. Pondering the solution space of available parts suggests a COB LED on a flexible gooseneck, which led to some 30 cm USB extenders, then smashing one of the connectors to reveal the wiring inside:

USB Gooseneck Extender - disassembled

USB Gooseneck Extender – disassembled

It was (probably) assembled by soldering the USB terminals to the wires, mounting it in a fixture, then injection-molding the shell around everything. The injected plastic fills the end of the gooseneck and immobilizes the wires.

I’d like slightly longer wire ends, although they’re workable if I don’t make any further mistakes. Perhaps I can heatsink the gooseneck, slit 10 mm of the metal sheath with an abrasive wheel, and peel off the pieces without damaging the wires. It could happen!

Speaking of mistakes, wiring an ordinary USB connector with +12 VDC for an LED seems fraught with peril…

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Electronics vs. Dark Rooms

Despite its diminutive size, the white LED on the end of the Dell AC511 USB SoundBar lights up a dark bedroom surprisingly well:

Dell AC511 USB SoundBar - white power LED

Dell AC511 USB SoundBar – white power LED

That’s pretty much the only power-on indicator for the streaming players, so I didn’t want to just slap a strip of black tape over it. Instead, because white LEDs don’t emit much energy toward the red end of the spectrum, I made a cute little filter from a snippet of Primary Red gel filter material, surrounded by a black Gorilla Tape donut:

Red filter for Dell AC511 USB power LED

Red filter for Dell AC511 USB power LED

Two layers of Primary Red cut the light intensity to a dim glow that’s barely visible in daylight and completely inoffensive at night:

Red filter for Dell AC511 - installed

Red filter for Dell AC511 – installed

The blue activity LED on the SunFounder got the black electrical tape treatment, however, with just a sliver showing through to give a hint that it’s still active:

SunFounder RT5370 USB WiFi Adapter - masked LED

SunFounder RT5370 USB WiFi Adapter – masked LED

One of the other WiFi adapters has a pinhole over a red LED that’s barely visible. Another, seemingly identical one, lacks the red LED under the pinhole; when I asked the vendor about that, I was told it was removed “to save power.” Yeah, right. That was part of the motivation to try a different adapter next time around, with good results.

Of course, you must wrap an opaque black case around the Raspberry Pi to tamp down the red and green LEDs on the PCB. It’s possible to control them in software, with varying degrees of difficulty depending on which Pi you have, but …


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Raspberry Pi 3 Reset Switch

The (relatively) new Raspberry Pi 3 PCB layout puts the Run header in a different location than in the Pi 2, but a minute of filing gnaws a suitable opening:

Raspberry Pi 3 - Reset Switch

Raspberry Pi 3 – Reset Switch

As before, a hot-melt glue blob holds the switch in place. I’d prefer a black case, if only to hide the blob, but clear-ish is what’s available right now.

Remember those orderly shutdowns, even at the cost of a keypad button!


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Cast Iron Pan Seasoning: Round 3

After seasoning the pan after every meal for a few weeks, then not doing that for a few more weeks, its thick glaze began looking somewhat scuffed:

Cast Iron Pan - scuffed

Cast Iron Pan – scuffed

You may recognize some of those scars from the previous picture:

Wagner skillet - two weeks of use

Wagner skillet – two weeks of use

Perhaps the multi-layer seasoning was entirely too thick and prone to chipping; this time, I’ll try a thinner coating. Because it’s cast iron, the pan under the coating remains undamaged.

A few hours in a bucket of sodium carbonate solution with a battery charger driving a few amps through it removed most of the glaze and a few minutes with a sponge sanding block cleaned off the rest. Applying flaxseed oil and heating it to 400 °F on a regular burner (under close supervision!) produced a nice coating:

Cast Iron Pan - seasoned

Cast Iron Pan – seasoned

The single layer was way slick for veggies in the evening and handled the morning omelet with aplomb, so we’ll run with it until something interesting happens.

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Respooling Stainless Steel Thread: The Knack

The comments on my previous stainless-steel thread respooling attempt suggested that I was entirely too much of a sissy, so, when another empty spool appeared, I tried again with more vigor:

Stainless steel thread - second spool

Stainless steel thread – second spool

As before, I put the larger spool on the floor under the lathe and let the thread spill straight off the top toward the smaller spool. This time, I didn’t have a twist accumulating in the loose thread between the two spools:

  • Grab longer lengths of the loose thread
  • Absolutely no slippage between the fingers!
  • Put more tension on the thread at the takeup spool

As nearly as I can tell, the thread still has a slight twist coming off the larger spool, but grabbing longer lengths captures the twist and more tension lays it on the smaller spool. After cutting the thread, what was left had maybe three turns of twist, which was no big deal and obviously hadn’t accumulated.

Seems better: thanks for all the comments!