Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
So I bought some LM12UU linear bearings from a nominally US-based eBay seller and received a suitably marked bag:
eBay – LM8UU bearings in LM12UU bag
They looked a bit on the skinny side:
eBay – LM8UU bearing
It seems somebody in the supply chain wasn’t paying attention, which isn’t surprising given the its ability to deliver ten hunks of reasonably precise machining to my mailbox for a buck-and-a-half apiece.
As it happens, I already have far too many LM8UU bearings and, after some unavailing back-and-forth with the seller, eBay customer service determined neither of us was “at fault” and refunded the whole order.
Being in no particular hurry, I ordered the next lot from halfway around the planet. Apparently, I’m now known throughout the land:
eBay – drop-ship addressing
Another label atop that one sported my actual address, with a matching Orange Connex tracking number barcode. Turns out OC is a “a joint venture between a leader in Chinese private equity investment, CITI CPE, and the a [sic] pioneer of global e-commerce platform, ebay”.
AFAICT, containers of “direct from China” packages arrive in the belly of a cargo airplane, get a sticker with their final destination, and enter the US postal system. It’s not clear buying from a “US seller” changes anything, as many of those packages come from addresses matching a building next to an airport.
This came about while tinkering up a shade for a repurposed LED downlight:
PVC fitting – boring setup
It’s a 4 inch DWV pipe coupling I bored out to fit the LED housing, which was ever so slightly larger than the pipe OD.
Cutting it off required as much workspace as the poor little lathe had:
PVC fitting – cutoff setup
Ignore the toolpost handle across the top. What’s important: the cutoff blade poking out of the QCTP, above the orange carriage stop lock lever, extending just far enough to cut through the coupling’s wall before the compound hits the coupling. The compound slide is all the way out against the cross-slide DRO, rotated at the only angle putting the tool where it needs to be and clearing the end of the coupling.
It ended reasonably well:
PVC fitting – LED floor lamp
But, in retrospect, was hideously bad practice. Next time, I’ll make a fixture to hold the fitting on a faceplate.
The far end has a 2.5 mm hex driver, although I’ve never encountered a nut for an M1×0.25 screw in the wild. It doesn’t fit an 0-80 nut and gulps 00-90 nuts, so it’s definitely hard metric.
My collection of glasses required an aggregate two turns of tightening, which prompted dBm to remind me of threadlock.
Mary made a batch of veggies in tomato sauce and froze meal-size portions as winter treats. The moist air inside the containers froze into delicate ice blades on the zucchini slices:
Veggie ice crystals – overview
A closer look:
Veggie ice crystals – detail
The blade cross-sections might be oblong hexagons, but it’s hard to tell with crystals melting almost instantly after the lid comes off. Some of the smaller hair-like blades reminded me of tin whiskers.
It’s been quite a while since BIOS boot sequences started with the floppy drive. Combined with a CMOS backup battery failure, I’d say this poor PC has been chugging along for two decades.
On another floor:
Kiosk – Windows Updates
Isolating a Windows kiosk from the Interwebs is an excellent design principle, but Windows Update really wants to phone home. The kiosk’s presentation ran Adobe Flash 10, so it’s been confined for maybe a decade.
Looks like it’s time for another fundraising drive to replace the PCs with Raspberry Pi controllers. The real expense, of course, goes into rebuilding the presentations using whatever tech stack is trendy these days.
Following a linkie I can no longer find led me to retrieve the Tektronix Circuit Computer in my Box o’ Slide Rules:
Tektronix Circuit Computer – front
I’m pretty sure it came from Mad Phil’s collection. One can line up the discolored parts of the decks under their cutout windows to restore it to its previous alignment; most likely it sat at the end of a row of books (remember books?) on his reference shelf.
The reverse side lists the equations it can solve, plus pictorial help for the puzzled:
Tektronix Circuit Computer – rear
Some searching reveals the original version had three aluminum disks, shaped and milled and photo-printed, with a honkin’ hex nut holding the cursor in place. The one I have seems like laser-printed card stock between plastic laminating film; they don’t make ’em like that any more, either.
TEK PN 003-023 (the paper edition) runs about thirty bucks (modulo the occasional outlier) on eBay, so we’re not dealing in priceless antiquity here. The manual is readily available as a PDF, with photos in the back.
Some doodling produced key measurements:
Tektronix Circuit Computer – angle layout
All the dimensions are hard inches, of course.
Each log decade spans 18°, with the Inductive Frequency scale at 36° for the square root required to calculate circuit resonance.
Generating the log scales requires handling all possible combinations of:
Scales increase clockwise
Scales increase counterclockwise
Ticks point outward
Ticks point inward
Text reads from center
Text reads from rim
I used the 1×100 tick on the outer scale of each deck as the 0° reference for the other scales on that deck. The 0° tick appears at the far right of plots & engravings & suchlike.
The L/R Time Constant (tau = τ) pointer on the top deck and the corresponding τL scale on the bottom deck has (what seems like) an arbitrary -150° offset from the 0° reference.
The Inductive Frequency scale has an offset of 2π, the log of which is 0.79818 = 14.37°.
The risetime calculations have a factor of 2.197, offsetting those pointers from their corresponding τ pointer by 0.342 = log(2.197) = 6.15°.
A fair bit of effort produced a GCMC program creating a full-size check plot of the bottom deck on the MPCNC:
By the conservation of perversity, the image is rotated 90° to put the 1 H tick straight up.
The 3018 can’t handle a 7.75 inch = 196 mm disk, but a CD-size (120 mm OD) engraving came out OK on white plastic filled with black crayon:
Tek CC bottom – ABS 160g 2400mm-min
The millimeter scale over on the right shows the letters stand a bit under 1 mm tall. And, yes, the middle scale should read upside-down.
Properly filling the engraved lines remains an ongoing experiment. More downforce on the diamond or more passes through the G-Code should produce deeper trenches, perhaps with correspondingly higher ridges along the sides. Sanding & polishing the plastic without removing the ink seems tedious.
The Great Dragorn of Kismet observes I have a gift for picking projects at the cutting edge of consumer demand.
More doodles while figuring the GCMC code produced a summary of the scale offsets:
It turned out easier to build vectors of tick mark values and their corresponding lengths, with another list of ticks to be labeled, than to figure out how to automate those values.
The Smell of Molten Projects in the Morning 