Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
A hinge started squeaking, which required nothing more than a long pin punch, a soft hammer, and a dab of oil.
The unplated steel hinges in our house date back to the middle of the last century and all of them have a convenient hole in the bottom for a pin punch: much fancier than the raw edge of the folded frame and the butt end of the hinge pin. You drive the hinge pin upward with a few taps, lube it, and tap it back in again with a soft hammer (perhaps against a folded rag), and you’re done.
On the other side of door, however, lies one of our follies. For reasons that made perfect sense at the time, the hallway has five different shades of white paint:
Flat walls
Eggshell ceiling
Gloss trim
Semigloss front door
Epoxy hinges
The hallway has three branches, two openings, and ten doors. The white really sets off the hardwood floors and doors, while brightening what would otherwise be a rather dim area, but never, ever again will we make that mistake.
On the other paw, the hinges came out well. I took them off all those doors and jambs, cleaned the steel, gave ’em two rattle coats of white epoxy, and reinstalled. Much nicer than contemporary “shiny brass” plating or raw steel.
Back when I got a Philips Sonicare (on the recommendation of my dental hygenist, after a particularly nasty bout of plaque removal), the battery gave nearly two weeks of service between charges. As shown in that graph, the runtime gradually faded away to two days, at which point I decided it was time to tear the thing apart and see about replacing the batteries.
The instruction manual tells how to dismantle the case and extract the NiCd battery for recycling:
Please note that this process is NOT reversible.
Well, there’s a challenge if I ever read one, but Wouldn’t It Be Nice If you could take something apart, unplug its defunct battery, install a new one, and button it up again? Then you wouldn’t be forced to buy a new $70 toothbrush, which probably explains everything… and I suppose the replacement battery would cost $40, even if it were a pair of AA cells.
For reference, the instructions (clicky for more dots):
As predicted, suasion applied through a small screwdriver popped the top end of the case apart, but the remainder required concerted prying and muttering. The case halves mate with a tongue-and-groove joint that’s either sonic welded or adhesive bonded to form a watertight seal all the way around, to the extent that they suggested cleaning the thing in a dishwasher.
Eventually, though, it came apart:
Sonicare – case opened
The “motor” (actually, a solenoid that couples to the magnet on the brush stem) is firmly potted in place (on the right), as are the NiCd cells and the charging power pickup coil at the base on the left. The potting compound seems to be a clear epoxy, rather than a compliant rubber, and it doesn’t bond to the case at all. It is, however, a perfect fit and doesn’t pop loose without a struggle; their instructions will definitely break the PCB.
Seen from the other direction, six connections join the PCB to those immovable objects. The four pins (on the far left) go to the solenoid and the pair (just to their right) to the battery:
Sonicare PCB solder points
A few dabs of desoldering wick suffice to free the pins and release the PCB. Mercifully, the potting compound surrounding the charging coil slid out easily, as they (inexplicably) omitted a mechanical lock molded into the case:
Sonicare – PCB removed
Removing the NiCd cells required considerable prying, as described in the instructions, that en passant damaged their cases. I think if you weren’t paying attention, you could easily rupture a cell case with the screwdriver and spatter the area with potassium hydroxide, perhaps shorting the cell in the process and producing rather more excitement than most folks expect.
A closeup of one cell; the other bears similar damage:
Sonicare – damaged NiCd cells
I snipped off the cell tabs and applied them to the new NiMH cells. A bit of closed-cell foam between the cells and the PCB cushions the assembly:
Sonicare – new NiMH cells on PCB
Stacking more foam snippets under the cells filled the space left by the potting compound, then soldering the solenoid pins held everything together:
Sonicare – new NiMH in place
A wrap of clear adhesive (rather than the obligatory Kapton) makes for a tidy joint that probably won’t last very long, but it looks much the way it did before the operation. The case is no longer waterproof and won’t withstand the dishwasher. In fact, I must now store it with the brush end downward to keep the last few drops out of the handle.
There’s an interesting solder jumper on the PCB that I didn’t bridge, but the next time it’s opened up I’ll apply a dab:
Sonicare – BLINKY jumper
The alert reader will notice that I’ve replaced 2000 mA·h AA NiCd cells with 600 mA·h 2/3 AANiMH cells, without changing the charger. The power transfer through the inductive coupling drives a trickle charger at about one hour of recharge per brushing, so there’s not much danger of overcharging the cells.
Now, to discover what runtime fresh cells deliver. This calls for another slip of geek scratch paper in the bathroom.
Being that type of guy, I noted each date when my Sonicare toothbrush needs recharging, at least after the battery had declined to about a week between charges, specifically so I could produce this graph:
Sonicare Runtime
The peaks include trips where I didn’t use the toothbrush and I’ve certainly blundered a few dates, but you can eyeball a trendline: those cells are kaput!
In round numbers, I bought the thing in early 2010, so the cells lasted maybe 2-½ years. I routinely run the toothbrush until the blinky light indicates that it needs charging, then fill it up overnight, to avoid having the cells fail like the ones in the beard trimmer.
Somehow the notion of discarding the whole toothbrush seems wrong, even though the instruction manual describes how to remove the battery for recycling before you junk the carcass. Talk about planned obsolescence!
While doing something else, I rediscovered the fact that common 5 gallon plastic bucket lids have an O-ring gasket that seals against the top of the bucket. Some seals are hollow tubes, some are solid rods:
5 gallon can lid gaskets
The white O-ring has about the right consistency to serve as a quilting pin cap, along the lines of those 3D printed and silicone rubber filled cylinders. Although the rubber / plastic stuff isn’t quite as squishy as silicone snot, it holds the pin point firmly without much of a push.
Chopping the O-ring into 10 mm sections produced another small box of prototypes:
Lid gaskets as pin caps
Garden planting season remains in full effect, shoving all quilting projects to the back burner and delaying the evaluation phase of the project…
Mary uses an ancient paring knife (that, back in the day, my father had sharpened beyond all reason) to harvest garden veggies, which called for a scabbard to protect the blade, the bike pack, and the fingers.
I snagged a random block of acrylic from the heap, straightened the long sides, milled a channel just wide and thick enough for the blade down the middle, then added small recesses at the right end for the knife’s haft:
Garden knife scabbard – main block
The cover is an acrylic sheet, solvent-glued and clamped in place:
Garden knife scabbard – clamping cover
The cover exposes about 1/4 inch of channel so she can lay the point in place, rather than precisely aligning the point with the slot. I suppose I should have used gray acrylic to provide some contrast; maybe we’ll add a snippet of tape.
Then mill four sides flat, break the edges & corners with a file, and it’s all good (in a blocky kind of way):
Garden knife scabbard
The blade has become sufficiently bent over the years that simple friction holds it in the slot. It’s open on both ends so she can flush out the inevitable dirt.
I was going to engrave her name on the back, but came to my senses just in time…
They’re rated at 600 mA·h, as are the much shorter 2/3 AA NiMH cells I also used for those phone packs:
Norelco T770 – rebuild
That’s a wrap of Kapton tape around the cells, plus a block of closed-cell foam to fill the cell holder. It’s not a high-stress environment, so this hack-job repair should work fine.
The trimmer’s charge / discharge cycle remains hostile to NiMH cells and I don’t expect a great lifetime from the new cells, either…
A long-forgotten toy emerged from the heap bearing a trio of corroded NiMH cells between the usual plated-steel contacts:
Corroded contacts – original
The toy wasn’t worth salvaging, but I extracted the contacts and applied Evapo-Rust to see what happened. After an overnight soak, some corrosion remained:
Corroded contacts – after Evapo-Rust
Scrubbing with a stainless-steel detail brush removed the flakes and left reasonably clean metal behind:
Corroded contacts – after brushing
Although it’s not beautiful, I think the contacts came out as well as one could expect. The longer contact plate has holes, thinned sections, and some corrosion inside the spring; I’d be mildly tempted to rebuilt the whole thing with some nickel shim stock and a new spring.
If I were salvaging the toy, I’d dab vinegar on the wiring to neutralize the creeping potassium hydroxide, rinse the whole thing with water, and clean out the case. Instead, it joined the consumer electronics recycling box with a thud…
The Smell of Molten Projects in the Morning 