Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The horrible paint crazing came from “priming” the bare plywood scrap (yes, that’s a stray hole from its previous life) with a specialty white paint intended for plastic lawn furniture; it apparently gets along poorly with the forget-me-not fluorescent red topcoat. Doesn’t matter in this application and uses up more of both rattlecans, so it’s all good.
Of course, after tucking it in the bike’s underseat bag, I spotted the lost plate along the DCRT: now I have a spare!
The discussion following that post on getting feature coordinates from an existing part reminded me of an old project that I’d written up for Digital Machinist: making repair parts for the half-century old storm doors on our house. Here’s the whole latch, with a replacement drawbar and cam:
Latch Assembly
The other side of the drawbar and cam:
Door Latch Parts
An early version of the drawbar that engages the latch strike and gets pulled by cam:
New and Old latch pulls
Three iterations on a cam; the messed-up one in the center, IIRC, helped track down an EMC2 bug:
Latch Cams
Now that I look at it again, there’s nowhere near enough meat around that square hole for a 3D printed plastic part… so the notion of printing the complex part of the cam and adding wear bars along those ears just isn’t going to work.
I made a fixture for the Sherline CNC mill to hold the drawbar for inside milling:
Latch pull – Inside milling
Then a block screwed down in the middle clamps the drawbar in the same place for outside milling:
Latch pull – Outside milling
The square post in the left rear corner holds the cam:
Latch Cam – First Attempt
Note that I had to file the square hole before milling the cam shape, which meant that if the CNC process screwed up, all that handwork went into the show-n-tell bin… which I’m not going to show you.
I used an early version of the grid-overlay technique to map out the drawbar coordinates; this was an illustration for the column:
I needed a rail-to-rail op amp in a DIP package to breadboard the amplifier for those toroids and came up dry, so I sawed out a protoboard square, glued a MAX4330 in SOT23-5 atop it in classic dead-bug style, rearranged the leads into the standard DIP pinout, and moved on:
MAX4330 dead-bug style on DIP adapter
The trick to getting the header pins aligned is to stick ’em in a pile of perfboards, which instantly makes them stand up straight and parallel:
Decades ago, one jaw on my little 1/4 inch wrench that fits 4-40 nuts broke off. I brazed it back on, fully aware that one day it would break off again, because brazing isn’t really a suitable repair technique for a wrench, even one labeled as “Precision” in that time-honored manner of all low-cost tools.
Time passes, I’m tightening screws against 4-40 nuts, and the jaw gives way:
Precision wrench – broken jaw
So I sawed off a strip of bedframe steel that fit the nuts better than the original stamped steel, did a bit of hand filing, and came up with a reasonable replacement:
Precision wrench – detail
I rammed it into the handle, just as they’d done with the original stamped steel shape:
If you happen to own an MFJ-260B dummy load and it’s giving you weird SWR values, take the cover off and roll the power resistor in its mounting clips:
MFJ-260B HF Dummy Load – power resistor
My buddy Aitch discovered that oxide / corrosion / dirt buildup between the resistor and the clips can produce absolutely baffling results, even while passing enough current to warm up the element, far more power than you’d think would burn away any crud.
Evidently, it’s impossible to make a spring both good and noncorrosive:
Garden sprayer – corroded spring
I found a suitable (i.e., good, but rust-prone) spring in the Big Box o’ Medium Springs:
Garden sprayer – spring replaced
Unlike the repair for that sprayer, this spring turned out to be long enough to work perfectly. I have no idea how long I can keep this up, but … at least I’m now keeping pace with the failures.
One of my fundamental rules is that you should never, ever look inside the water lines serving your faucets. Having recently replaced a water heater, I had to violate that rule and discovered this growth inside the flex tube at the hot water outlet:
The Smell of Molten Projects in the Morning 