Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
I’ve always wondered what’s inside a metal-case vacuum tube:
Dual rectifier tube 5T4 – metal case opened
The cutter last saw action on the EMT used in the MPCNC, so it’s intended for use on steel tubes. I thought about parting the case off in the lathe, but a tubing cutter sufficed for a first attempt, even if it couldn’t cut quite as close to the flange as I wanted.
A 5T4 tube is a full-wave rectifier with two sections:
Dual rectifier tube 5T4 – upright
Unsurprisingly, the guts resemble those of glass-envelope rectifier tubes in my collection, like this 5U4GB:
5U4GB Full-wave vacuum rectifier – cyan red phase
The metal case would be far more rugged than a glass bottle and, perhaps, the flange locked the tube into its socket against vibration.
The filaments surely weren’t thoriated, so it’s all good …
A new spool of retina-burn orange PETG snagged when the takeup guide let the filament fall off the inboard side and the extruder tightened the loops around the spool holder. I carefully unwound the loops without removing the spool to ensure I didn’t introduce a crossover, scraped the bird’s next off the platform, and restarted the print.
After undoing the second snag, I added a crude spool sidewall:
I’ll probably regret not adding pins along the entire row, but, unlike the MPCNC, the CNC 3018XL won’t ever have hard limit switches. I plugged the Run-Hold switch LEDs into an unused +5 V pin and moved on.
As is my custom, the day before showtime I talked my way through a final full-up dress rehearsal, with the HP 7475A plotter and the CNC 3018XL running their demo plots. As if to justify my attention to detail, the 3018 refused to home, with its X axis motor grinding in a manner suggesting something had gone terribly wrong with its driver.
OK, I can fix that™.
Turn off the power, verify the leadscrew turns smoothly by hand, check all the connections & connectors, then pull the DRV8825 PCB to see if anything looks obviously wrong. It didn’t, so I carefully re-plugged the driver and moved the whole affair to the Electronics Workbench for further study.
I turned on the scope and Tek current probes, then turned on the 3018 power supplies, whereupon a great cloud of Magic Smoke emerged from the CAMtool board and filled the Basement Laboratory with the acrid smell of Electrical Death.
It seems I carefully and meticulously re-plugged the DRV8825 PCB into its socket exactly one pin too high, which, among other Bad Things, connects the +24 V motor power supply to the driver GND pin.
Obviously, this did not end well:
CAMtool V3.3 – blown stepper fuse
The fuse, put under considerable stress, vented smoke & debris in all directions across the board; note the jets above the white motor connector. Surprisingly, the 1 kΩ resistor just below it is in fine shape, as is the rather blackened electrolytic cap.
The fuse measures the same 150-ish mΩ as the fuses in the other two axes, but I doubt it’s actually a fuse any more.
Astonishingly, the Arduino clone on the board worked fine, so I could extract the GRBL configuration.
Memo to Self: Never plug things in with your head upside down!
Along with the (defunct) Blackburn Flea, the bike pack also disgorged an anonymous taillight with a battery resistant to recharging through the USB port. Gentle suasion cracked the solvent-glued joint around the case:
Bike taillight – cracking case
As with most modern electronics, a battery occupies most of the interior volume:
Bike taillight – opening case
For posterity, the connections:
Bike taillight – connections
I unsoldered the cell and charged it from a bench supply:
Bike taillight – external recharge
The voltage started out low with the current held to about 100 mA, eventually rose to 4.1 V, and stayed there while the current dropped to zero. Unlike the Blackburn cell, it appears not too much worse for the experience, although I haven’t measured the actual capacity.
Clipping the Tek current probe around the LED supply wire produced this waveform for the “dim” setting:
Anonymous Taillight – Low – 200 mA-div
Adding a voltage probe across the LEDs and clicking to the “high” setting:
Anonymous Taillight – High – 200 mA-div
The intense ringing at the start of the pulse seems an artifact of the measurement setup, but ya never know; these days, RFI can come from anywhere.
In any event, the COB LED strip draws 800 mA from a fully charged battery, about 26 mA for each of the 30 LEDs. The 5% duty cycle in the “dim” setting is decently bright and 18% in “high” is entire adequate.
A trio of blinks works for daytime rides, although the fastest one seems seizure-inducing.
I’ve strapped it around a rack strut and run it at the slowest blink, on the principle you can never have too many blinky lights …
You’re supposed to just rotate the wiper blade holder and have it pop out of the mount on the end of the arm:
Subaru Forester – rear wiper blade mount
The blade holder has two opposed pegs fitting into those curved notches to the right of the hook for the holder’s pivot, with the intent of preventing it from rotating too far and sliding out. I was unwilling to apply sufficient force to disengage those pegs, as the penalty for breaking the wrong piece of plastic seemed very high. Apparently, the pegs should ride up over the slightly lower edge of their notch, bending the holder’s sides outward as they do.
So I jammed a little screwdriver beside one of the pegs, managed to encourage it out of its notch, repeated the treatment on the other side, and the blade holder popped right out.
The front wiper arms have J-hooks on their ends and disengage easily, at least after you realize the flat panel on the blade holder is actually a latch you’re suppose to pull up-and-out to release the hook. This goes more easily when assisted with the aforementioned small screwdriver.
The blades were in good shape after five years, mostly because the Forester spends most of its time in the garage. A trio of silicone wipers should last the rest of its life, with the OEM wipers tucked into the spare tire well Just In Case.
Back in the day, one could replace just the blades, not the entire holder, but I suppose this is progress.
A dark ring of epoxy around the screw holds a shortened M3 brass insert in place:
Pilot V5RT holder – lock screw insert
As it turned out, the original recess left only a few threads for the M3 SHCS, so the much longer screw wobbulated alarmingly. I drilled out the threads, turned the knurls off the insert, shortened it a bit, masked the pretty knurls on the aluminum ring, then glopped the insert in place while the Sherline held the screw vertical:
Pilot V5RT holder – insert epoxy
While I was at it, I added a thin ring of foam rubber under the knurled ring to keep it from clacking against the upper bushing.
Now I can’t lose the hex wrench when I take the thing out for Show-n-Tell sessions …
The Smell of Molten Projects in the Morning 