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

Multimeter Range Switch Contacts: Whoops!
One of my multimeters began reporting bogus values that improved by working the range switch back-and-forth, which suggested the switch contacts need cleaning. Taking the meter apart was easy, right up to the point where I removed the range switch from the PCB by compressing the four locking tabs on the central shaft:

Multimeter range selector switch

Just before taking that picture, the switch launched half a dozen spring contacts across the bench, my shirt, and the floor… I recovered four for the picture and later found a fifth smashed on the floor, but the last contact remains AWOL.

The contact in the middle, the oddly shaped one with small tabs on the ends, is a prototype replacement conjured from 6 mil phosphor bronze stock:

Multimeter range switch contacts

The little domes ensure a good sliding surface, but require two bends in the middle of the contact and some way to shape the metal into a dome. After a few experiments, I filed the end of a nail into a rounded chisel that worked pretty well:

DMM switch contact punch

The original contacts came from 3.5 mil stock and have considerably more flex; 6 mil stock is what I have.

I think I should make half a dozen contact springs to replace the entire set, a task requiring more time than I have right now. For the record, the overall process goes like this:
- lay out overall shape, slightly longer than needed
- cut center opening with abrasive wheel
- cut out contact
- punch contact domes (from back = dimples)
- bend to shape
- trim ends to length (not done in picture)
- dress raw edges (not done in picture)
Given the number of parts and the fiddly accuracy required to make the slot, this might be a good job for the Sherline, although clamping each little proto-spring down while getting the abrasive wheel in there seems daunting.

Perhaps cutting the slots and punching the dimples would work better before cutting out the contacts, with a sheet clamped on four sides? The center will be floppy, what with all the slots, but grinding slots on the middle contacts first might be helpful. Would adhesive under the sheet to hold down the middle gunk up the abrasive wheel?

So many projects …

Memo to self: Springs! Always expect springs!
2012-09-20
Black and Decker Pocket Power: Battery State

A Black & Decker Pocket Power emerged from the heap and refused to take a charge, which obviously calls for a teardown. The case has three screws, one lurking behind the label:

Pocket Power – case screws

The sticker over on the right says it’s five years old, which explains the whole problem right there; you can evidently buy new-old-stock units from the usual low-dollar sources that will arrive with a similarly dead battery.

Peeling off the rubber bumpers and prying the case open reveals the innards:

Pocket Power – internal layout

The battery pack looks to be an octet of ordinary NiMH cells; the label on the other side of the shrink wrap reports 9.6 V @ 1200 mA·h, which is about what you’d expect, with a date in mid-2007 that matches the sticker on the case.

The upper left corner of the main label has some interesting information:

Pocket Power – label specs

The tiny wall wart that came with the unit produces 12 VDC at 300 mA, which doesn’t match the INPUT spec at all. Perhaps the maximum current from the internal pack made its way to the label by mistake?

The label also shows the reason I got this thing: it can produce just enough 120 VAC power to run an arbitrary wall wart charger for a gadget that doesn’t charge from a 12 VDC source. Upconverting 9.6 VDC to 120 VAC, then downconverting it to, say, 14.4 VDC makes no sense whatsoever, unless that’s the only way to charge that particular gadget. Which has, I’m sorry to say, been the case every now and again.

I think the Model name has a typo: everything else suggests this is a CP120B. So it goes.

Unsoldering the leads and perpetrating the obvious tests produces these curves:

B&D Pocket Power

The black curve is the initial “won’t accept a charge” state with the wall wart and internal circuitry; the pack obviously has two weak cells. The curves in the lower left correspond to individual cells and series pairs that I discharged to 0.9 V/cell after the top curve ended.

The tiny stroke between the sets, way over on the Y axis, is cell pair BC (my arbitrary labels) that probably accounts for the sudden drop in the black curve. However, the orange curve also came from pair BC after charging for about 18 hours at 120 mA, so they’re not completely dead. Their capacity has dropped to about 700 mA·h, though, which isn’t good.

Soldering the pack back together and charging for another 18 hours at 120 mA produced the green curve at the top, which shows the same sudden dropoff at about 700 mA·h.

So I’ll put it back together again and let it charge for a while, but new cells will definitely brighten its disposition.

2012-09-19
Wouxun KG-UV3D: Improved Knob Index

After Raj thoroughly shamed me for slobbering white glop on the KG-UV3D’s volume / power knob, I hereby repent…

Clamp a cutoff chunk of 3/16 =0.1875 inch diameter brass tubing in the lathe and file down one side to put the flat 0.150 inch from the far side, so that the knob is a tight slip fit. If you happen to have some solid rod, that would work just as well. In this case, the file pushed the paper-thin brass remnant into the tubing and I didn’t bother to clean it out:

KG-UV3D knob with fixture

Clean the white glop off the knob, jam the knob on the fixture, clamp the fixture in the Sherline’s vise, use laser targeting to center the spindle on the notch adjacent to the minuscule pip on the knob:

Laser aligning to knob feature

Drill a 2 mm recess that en passant obliterates the pip:

Drilling index recess

Fill it with some light gray paint that just happens to be on the shelf:

Knob with filled index mark

And, by gosh, it really does dress up the radio! [grin]

Wouxun KG-UV3D with improved knob

While I had the Sherline set up, I did the knob for the other radio, too.

Thanks, Raj… I needed that!

2012-09-12
KG-UV3D GPS+Voice Interface: APRS Bicycle Mobile

Wouxun KG-UV3D with GPS-audio interface

Both of the GPS+voice interfaces for the Wouxun KG-UV3D radios have been working fine for a while, so I should show the whole installation in all its gory detail.

If you haven’t been following the story, the Big Idea boils down to an amateur radio HT wearing a backpack that replaces its battery, combines the audio output of a Byonics TinyTrak3+ GPS encoder with our voice audio for transmission, and routes received audio to an earbud. Setting the radios to the APRS standard frequency (144.39 MHz) routes our GPS position points to the global packet database and, with 100 Hz tone squelch, we can use the radios as tactical intercoms without listening to ~~all~~ much of the data traffic.

The local APRS network wizards approved our use of voice on the data channel, seeing as how we’re transmitting brief voice messages using low power through bad antennas from generally terrible locations. This wouldn’t work well in a dense urban environment with more APRS traffic; you’d need one of the newfangled radios that can switch frequencies for packet and voice transmissions.

So, with that in mind, making it work required a lot of parts…

Tour Easy – KG-UV3D GPS interface

A water bottle holder attaches to the seat base rail with a machined circumferential clamp. Inside the holder, a bike seat wedge pack contains the radio with its GPS+voice interface box and provides a bit of cushioning; a chunk of closed-cell foam on the bottom mostly makes me feel good.

The flat 5 A·h Li-ion battery pack on the rack provides power for the radio; it’s intended for a DVD player and has a 9 V output that’s a trifle hot for the Wouxun radios. Some Genuine Velcro self-adhesive strips hold the packs to the racks and have survived surprisingly well.

Just out of the picture to the left of the battery pack sits a Byonics GPS2 receiver puck atop a fender washer glued to the rack, with a black serial cable passing across the rack and down to the radio bag.

A dual-band mobile antenna screws into the homebrew mount attached to the upper seat rail with another circumferential clamp. It’s on the left side of the rail, just barely out of the way of our helmets, and, yes, the radiating section of the antenna sits too close to our heads. The overly long coax cable has its excess coiled and strapped to the front of the rack; I pretend that’s an inductor to choke RF off the shield braid. The cable terminates in a PL-259 UHF plug, with an adapter to the radio’s reverse-polarity SMA socket.

The push-to-talk button on the left handgrip isn’t quite visible in the picture. That cable runs down the handlebar, along the upper frame tube, under the seat, and emerges just in front of the radio bag, where it terminates in a 3.5 mm audio plug.

The white USB cable from the helmet carries the boom mic and earbud audio over the top of the seat, knots around the top frame bar, and continues down to the radio. USB cables aren’t intended for this service and fail every few years, but they’re cheap and work well enough. The USB connector separates easily, which prevents us from being firmly secured to a dropped bike during a crash. I’d like much more supple cables, a trait that’s simply not in the USB cable repertoire. This is not a digital USB connection: I’m just using a cheap & readily available cable.

All cables converge on the bag holding the radio:

Tour Easy – KG-UV3D + GPS interface – detail

Now you can see why I put that dab of white on the top of the knob!

The bag on my bike hasn’t accumulated quite so much crud, because it’s only a few months old, but it’s just as crowded:

KG-UV3D + GPS interface on Tour Easy – top view

This whole “bicycle mobile APRS system”, to abuse a term, slowly grew from a voice-only interface for our ICOM IC-Z1A radios. Improving (and replacing!) one piece at a time occasionally produced horrible compatibility problems, while showing why commercial solutions justify owning metalworking tools, PCB design software, and a 3D printer.

I long ago lost track of the number of Quality Shop Time hours devoted to all this, which may be the whole point…

In other news, the 3D-printed fairing mounts, blinky light mounts, and helmet mirror mounts continue to work fine; I’m absurdly proud of the mirrors. Mary likes her colorful homebrew seat cover that replaced a worn-out black OEM cover for a minute fraction of the price.

2012-09-11
Wouxun KG-UV3D Volume Knob: More Black on Black

The volume / on-off control knob on our Wouxun KG-UV3D radios has the most minute raised dot you can imagine to mark its orientation. Yes, it’s another subtle black-on-black control! See if you can spot the dot:

Wouxun KG-UV3D – volume knob marking

The radio lives in a small pack attached to the back of the seat frame: we turn it with a fingertip and adjust the volume by touch; the dot is just barely perceptible to my finger. Nevertheless, WIBNI (Would It Be Nice If) you could look at the knob from a distance and determine whether the radio was turned on?

A dab of typewriter (remember typewriters?) correction fluid later:

Wouxun KG-UV3D – garish knob marking

Not elegant and sure to wear off after a while, but the smudge should remain visible forever.

2012-09-07
Updating An Old Bike

Rollfast bike with Aztek brake pads

Our Larval Engineer acquired a free bicycle to get around at school: a Rollfast “girl’s bike” dating back to 1972 with 105 miles on the odometer. She completely dismantled it, cleaned everything, reassembled it in reverse order, and added a rear rack & panniers. Having touched every part of the bike, she’s now in a much better position to fix whatever may go wrong in the future.

It was an inexpensive bike to start with and we left everything as-is, with the exception of the brake pads. You’re supposed to bend the brake arms to align the pads with the rims, a technique which I didn’t like even back in the day. So we swapped the OEM pads with worn-but-serviceable Aztek pads sporting spherical washers:

They’re way grippier than the old pads, even on those chromed-steel rims. I had a bike with steel rims and old pads; given the slightest hint of water, it didn’t stop for squat. With any luck, the Azteks will at least slow this one down.

Although she wanted to take the Tour Easy, the bike must live outside under the apartment stairs all year and, frankly, that’d kill the recumbent in short order. Forgive me for being a domineering parent; when she has a good place to store a spendy bike, it’s hers for the taking.

We haven’t figured out how to mount the GPS/APRS tracker + radio and antenna. The evidence suggests she prefers to travel incognito from now on…

2012-09-03
Rebalancing a Cheap Santoku Knife
So I bought a lurid green $8 Tomodachi Santoku knife at K-Mart, which was the first non-stick-coated Santoku-shaped knife I’d seen since that comment. It’s made by Hamilton Forge Ltd, one of those generic names that doesn’t produce any search results worth mentioning and so probably isn’t a real company:

Tomodachi Santoku knife

The knife has a huge steel blade with a solid plastic handle injection-molded around a short tang, which put the balance point maybe 50 mm out into the blade. I didn’t like the feel when I waved it around in the store and really didn’t like how it behaved on the cutting board.

The way I see it, I can fix a too-light handle…

Pursuant to that post, I have a bag of tungsten electrodes, some complete with a glass seal:

Tungsten electrode with glass seal

Wrapping some masking tape around the glass, tapping it with a hammer, then sliding the tape-with-fragments into the trash got rid of the glass. The bulbous tip seems to be a stainless steel tube welded around a thin tungsten shaft, so I clamped it in the vise and whacked it with a chisel; tungsten is strong-but-brittle and cracks easily:

Fracturing tungsten electrode

Of course, whacking a tungsten rod didn’t do the chisel the least bit of good, but it was about time to sharpen that thing anyway.

Why use tungsten electrodes instead of, say, ordinary drill rod? Tungsten has about the highest density you can get without going broke, getting poisoned, or dying of radiation exposure. That useful table gives elemental density in g/cm³:
- aluminum = 2.7
- iron = 7.9
- lead = 11.4
- gold = 19.32
- tungsten = 19.35
- osmium = 22.6
Can’t afford gold, not even I would put a lead slug in a kitchen knife, and I had the electrodes, so why not?

Waving a neodymium magnet over the handle convinced me that I could drill a hole slightly more than two inches deep without hitting the tang. I briefly considered drilling half a dozen smaller holes, but that started to look like a lot of work and I don’t have any suitable gun drills.

The business end of the electrode measures 1 inch long and 0.1375 inch in diameter. A hexagonal cluster of seven rods fits neatly into a round hole about 3×0.137 = 0.413 inch in diameter: quite conveniently a nice, long Z drill. So I clamped the knife between two strips in the drill press vise and had my way with it:

Drilling knife handle

Actually, I spot-drilled with a center drill, then used a long step drill, stopping with the 3/8 inch step just kissing the low side of the handle, to get the hole mostly on center, before running the Z drill down about 2-1/8 inch. The handle walls became so thin that they flexed around the drill to produce an undersized hole, so I reamed it with a hand-turned 7/16 inch drill and the electrodes fit with no room to spare:

Tungsten electrodes in knife handle

Yeah, that’s a crack in the top electrode: tungsten is brittle.

A dollop of epoxy atop the electrodes should seal them in place forever. I clamped the knife (in its color-matched scabbard) with the angled end of the handle water-level, so the epoxy settled in a neat, symmetric blob that looks better in person than it does here:

Epoxy seal over tungsten weights

The epoxy forms a plug over the ends of the electrodes and (probably) doesn’t extend very far down between them, but they’re firmly jammed in a snug hole and (probably) won’t ever rattle around.

Seven electrodes weighed 32 g and, figuring the missing plastic rounds off to slightly over nothing, the handle now has 60 g of additional weight out toward the end, producing a knife weighing 185 g that balances near the narrowest part of the handle. It’s somewhat heavier than I’d like, but I can cope.

The edge came from the factory reasonably sharp; a few passes over the sharpening steel touched it up nicely.

Early results: it cuts cheese perfectly, drifts to the right in melons, cuts wafer-thin slices from a loaf of my High-Traction Bread, and dismantles fruit with some clumsiness. Overall, I like it, although I could do without the bright green color in a big way.
2012-08-30