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.

Category: Machine Shop

Mechanical widgetry

CAMtool V3.3 vs. The Fat Fingers of Death

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!

2020-01-30
Anonymous Bike Taillight Current

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 …

2020-01-29
Subaru Forester Rear Wiper Disassembly

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.

2020-01-25
CNC 3018XL: Pilot V5RT Pen Holder Lock Screw

Flushed with success about the MPCNC drag knife locking screw, I installed a similar screw on the V5RT pen holder for the CNC 3018:

Pilot V5RT holder – lock screw insert – assembled

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 …

2020-01-24
Homage Tek CC Cursor: Pivot Milling
A test to mill the pivot hole in 0.5 mm PETG sheet worked perfectly:

Tek CC – cursor pivot hole milling

The cutter is a 3.175 mm = 1/8 inch router bit, one of a ten-pack that came with the CNC 3018 and to which I have no deep emotional attachment, held in a collet in the Sherline. The hole is 5.5 mm to fit an eyelet. The PETG is taped to a thin plywood scrap.

The hole happened by feeding G-Code manually into LinuxCNC, after touching off XYZ=0 at the center of the pivot and jogging up a bit:
```
g0 y-1.1625
f1000
g0 z0.5
g2 p5 z-1.5 i0 j1.1625
```
Yes, I engraved the hairline using a diamond drag tool on the CNC 3018, cut the cursor outline with a drag knife on the MPCNC, then milled the pivot hole on the Sherline. This seems way over the top, even to me, but that’s just how the tooling worked out right now.

In actual practice, I’d probably mill a stack of cursors and pivot holes on the Sherline in one setup, then engrave the hairlines in a suitable fixture. I think I know enough to fit a spring-loaded diamond drag bit into the Sherline’s 10 mm ID spindle or, worst case, conjure a block for the Z-axis carrier in place of the entire spindle mount.

At least now I can remember what I did to make the hole.
2020-01-22
MPCNC Drag Knife Holder: Lock Screw

While calibrating the MPCNC’s probe camera offset for the drag knife holder, this happened:

Drag Knife – vertical escape

Well, at least it’s centered on the target:

Drag Knife – vertical escape – detail

This happened a few times before, because my fingers don’t fit neatly inside the drag knife holder to tighten the lock ring:

Drag Knife – LM12UU ground shaft – assembled

[Update: The lock ring keeps the holder at a fixed position inside the 12 mm shaft and doesn’t affect the blade directly. When the ring works loose, the threaded holder can rotate to expose more blade and, in this case, stab deeper into the target. ]

So I turned & knurled an aluminum ring, then tapped a 3×0.5 mm hole for a lock screw plucked from the Drawer o’ Random M3 Screws:

Drag Knife – lock screw – side

A view looking along the screw shows a bit more detail around the spring:

Drag Knife – lock screw – front

The general idea is to set the blade extension, then tighten the lock screw to hold it in place, without relying on the original brass lock ring, shown here while cutting a boss for the spring:

Drag Knife – turning spring recess

The lock screw’s knurled handle just barely kisses the NPCNC’s black tool holder ring, so my guesstimated measurements were a bit off. Clamping the knife holder one itsy higher in the tool holder solved the problem.

I cranked on 300 g of spring preload and, squashed like that, the spring’s rate is now 75 g/mm. Cutting at Z=-1 mm should suffice for laminated paper slide rule decks.

The original sizing doodle:

Drag Knife Holder – lock screw ring doodle

The short 18 mm section clears the inside of the LM12UU bearing, although it could be a millimeter shorter. The 19 mm section comes from the 3/4 inch aluminum rod I used, skim-cut to clean it up.

If I ever remake this thing, it needs a major re-think to get all the dimensions flying in formation again.

2020-01-21
Photo Lamp Mount: Moah Plastic!

One of the cold shoe mounts I made for the photo lamps cracked:

$Photo Lamp Mount - fractured$
Photo Lamp Mount – fractured

It’s done in PETG with my more-or-less standard two perimeter threads and 15% 3D honeycomb infill, which is Good Enough™ for most of my parts. In this case, there’s obviously not nearly enough plastic in there!

Redoing it with three perimeters and 50% infill should improve the situation, even though it looks identical on the outside:

Photo Lamp Mount – reinstalled

I didn’t replace the other mount. If it breaks, it’ll get the same 50% infill as this one. If this one breaks, I’ll try 75%.

An easy fix!

2020-01-19