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.
Who’d’a thunk it?
Concerted rummaging in the Basement Warehouse produced some rather old acrylic sheets:
Washing with detergent and denatured alcohol cleaned off a lot of grunge, but the yellow tint says it’s been around for a while. In fact, It Came With The House™ when we bought it three decades ago.
One sheet was a status board in an automobile machine shop:
So, yeah, that might be 70-year-old acrylic.
A long-delayed bench cleanup united these two HP 09872-60066 digitizing sights:
I’ve used the one on the right (above) with my HP 7475A plotters, but the other sight obviously won’t fit:
The metal-shell version is advertised as “09872-60066 Calibration Pen for fit HP DesignJet 2000CP 2500CP 2800CP 3000CP 3500CP 3800CP Original New” which makes absolutely no sense, as those were inkjet and laser printers with (AFAICT) no need for a “calibration pen”. Because nobody with those printers will buy (or even look for) a widget they can’t use, the price is surprisingly low, compared to the real ones occasionally found on eBay.
My guess: somebody halfway around the planet found a pile of Genuine HP plastic snap boxes, filled them with knockoff sights vaguely similar to the original (perhaps intended for a different plotter?), and marketed them with the usual (lack of) attention to veracity.
Anyhow, we find our contestants standing in the light on a micropositioner under the microscope:
The old sight (genuine HP plotter) has a clean field of view:
With a tidy dot in the middle:
The new (to me, anyhow) sight has rather coarse hexagonal light pipes with gaps at the edges:
The spot at the middle is raggedly machined / drilled, with a bottom sufficiently un-flat to prevent focusing on the whole thing at once:
I have a vague project in mind to turn the new (craptastic) sight into an optical alignment punch, but the spot seems a bit too large for that.
The Huion tablet on my desk has its USB cable sticking straight out of the left side, whereupon it must loop around to burrow under the shelf under my monitor on its way to the port on the back of the PC case. The loop snagged on all the clutter atop the desk and I finally got around to Fixing That Problem:
Of course, it wasn’t quite that simple.
Right angle USB Mini-B connectors are still a thing:
Which is a “left angle” adapter and which is a “right angle” adapter depends on which supplier you ask and how much you trust their descriptions / product photos, so you should get a set containing both: it’s the only way to be sure.
The one on the right (a “right angle”) shows a bit of carving, which came after the completely unsurprising discovery that the stylin’ curves on the side of the tablet collided with the rectangular adapter:
Some diligent X-Acto knife work carved away enough of both the adapter and the tablet case to snugly join them:
The hackery over on the far right fits around the USB cable’s molded connector. I simply cut away any parts that touched until the adapter seated firmly in the USB socket and the cable exited parallel to the edge.
Part of this involved not carving deeply enough into the adapter or cable connector to expose the internal wiring. I assumed the tablet didn’t have anything vital immediately inside that fancy curve, so that’s where I dug deepest.
Stick adapter + cable to the tablet with good-quality electrical tape and now the cable points directly to where it should go.
Declare victory and move on!
Mary’s new sewing table just arrived, but the laser-cut acrylic insert fitting around her Juki sewing machine is still a month or two away. Until then, a simple cardboard replacement must suffice to fill the gap:
The rectangle just to the left of the needle is a hatch for bobbin changes. Sheer faith and an interference fit between layers of Kapton tape holds it in place with surprising force.
I wanted to tape the cardboard edges to the machine and the table to smooth out the transitions, but her Supreme Slider slippery sheet may solve the problem without adhesives:
The “insert” is a 1/4 inch thick double-layer corrugated cardboard sheet, utility-knifed from a huge box. She layers cardboard under the wood chips in her Vassar Farms garden paths to discourage the weeds; this seemed like a perfectly reasonable diversion.
Plotting the backlash / calibration target on both the CNC-3018XL and the MPCNC quickly showed, contrary to what I expected, the MPCNC was dead-on accurate, albeit with some wobbulation and a trace of backlash:
Although it looks ug-u-lee, the (lower speed) drag knife cuts come out nice and, because the entry and exit moves match the main cut, the minimal backlash wasn’t a problem.
Turns out only the X axis on the 3018XL had a problem:
Apparently the longer leadscrew I installed as part of the “XL” conversion has a small thread pitch error: about 1 mm short in every 250 mm of travel. I don’t have any (definite, non-handwavy) method to measure the pitch directly, other than by running the follower nut and measuring the results, but it’s consistently short.
Quite some time ago (after blowing up the OEM controller board), I set up the Protoneer CNC board in 1:8 microstep mode, making the GRBL $100 setting a nice, round 400 step/mm for a two-start leadscrew with 2 mm pitch and 4 mm lead:
400 step/mm = (200 step/rev * 8 µstep/step) / 4 mm
After a few more measurements suggesting the leadscrew actually traveled 249.2 mm, the correct value will be:
401.28 step/mm = 400 step/mm × 250 mm / 249.2 mm
To verify I understood the problem and solution, I set $100 to a few integer values around the goal:
The top image shows the leftmost line at the 10 mm mark on the scale, because it’s easier for me to match the ink line with an engraved line, rather than the non-line at the end of the ruler.
The other images show the results for $100 set to 399, 400, 401, and 402 step/mm, respectively. The results last two results bracket the desired 250 mm outcome, with 401 step/mm being Close Enough™. GRBL accepts a floating point step/mm value, so I set $100 to 401.28, but I was unable to convince myself the result came out consistently different than 401.00.
Plotting both the tick marks (green) and the knife path (red) on the 3018XL, then cutting the bare paper on the MPCNC, showed the two machines now agree on where the knife should fall. The outer end of the tick marks extends 1 mm beyond the cut line to ensure small misalignments do not produce an obvious white gap around the edge of the deck.
The Y axis continues to match:
And now the X axis looks just as good:
The drag knife corners are rounded, as you’d expect. The cut seems slightly offset from a small origin touch-off error, but the scales now match.
Found inside a fluorescent desk lamp being salvaged for possible use as an LED task lamp:
It’s one of the few Underwriter’s Knots I’ve ever seen in the wild. Many recent (i.e., built in the last half-century) lamps pass the cords through a plastic clamp or depend on simple bushings, with some just ignoring the problem.
This anonymous lamp sports the usual Made in China sticker, but also features a genuine-looking UL sticker complete with elaborate holograms, so it may well have been sold by a reputable company. IIRC, it came from a trash can in a Vassar College hallway, back when in-person meetings were a thing; perhaps Vassar required known-good electrical hardware.
Just before the turn of the millennium, I bought what turned out to be a never-sufficiently-to-be-damned HP 2000C inkjet printer that served as my introduction to refilling inkjet cartridges. A few years later, a Canon S630 printer joined the stable and worked fine for perhaps five years before succumbing to a printhead death. An Epson R380 that might have cost fifteen bucks after rebate took over, drank maybe a gallon of knockoff ink through a continuous ink supply system during the next thirteen years, and finally suffered progressive printhead failure during the last year.
Something recently changed in the inkjet market: Epson (among others) now touts their “Ecotank” printers featuring large internal reservoirs refilled by 70 ml bottles of color ink priced at perhaps 20¢/ml, obtained direct from Epson via Amazon. They proudly note you can save 90% off the cost of cartridges (“Kiss Expensive Cartridges Goodbye”), without mentioning how their previous extortionate cartridge business made that possible. Of course, Ecotank printers cost far more than cartridge-based printers, but that seems reasonable to me.
Because the ink bottles fit neatly into the printer through a push-to-flow valve interlock, I can finally retire this relic:
That’s maybe fifteen years of accumulated splotches.
I hope my refusal to buy their cartridges helped immanentize their eschaton, just a little.
Good riddance.
The Smell of Molten Projects in the Morning 