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

Resistance Welding: AA Cell Positive Terminal Gadetry

AA Cell Clamping Pliers

I’m trying to find out if I can use my hulking resistance soldering setup to weld nickel strips on AA cells, with the intent of making some decent 8-cell packs that don’t have crappy stainless-steel springs. Having slit the copper sheet for the jaws, I just now kludged together some electrodes…

The positive terminal on an AA cell is almost exactly 3/16 inch in diameter, call it 0.188 inches. That’s the hole in the middle of the copper sheet, which is neatly split so it clamps the terminal button from all sides with nearly equal griptitude.

The pliers are snap-ring pliers, with the original weird metric screws (neither 3 nor 4 mm, which is all I have) replaced with stainless steel 8-32 screws. Drill-and-tap the pliers jaws, clearance drill the not-quite-rectangular clamping plates, bend the jaws so the copper sheet aligns properly. It’s all good.

I plan to add a jumper connecting the two copper sheets; obviously, you don’t get good current transfer without a solid connection. The darker gold-copper color in the center section is Kapton tape insulating the top of the jaw sheets.

The cable goes off to one terminal of the resistance soldering transformer, which is a rewound kilowatt-class microwave oven transformer. The basics are 5 V RMS at about 200 A, with a foot switch into a microcontroller that drives a triac on the transformer primary. I can set the timing in multiples of 100 ms (6 AC line cycles) and the duty cycle from 1 to 6 of the cycles in each 100 ms. More on that later; the triac triggering is nightmarishly complex because I was doing a Circuit Cellar column and wanted to show how a triac gets all confused driving an inductive load. It really needn’t be that fancy in real life.

Anyhow, 200 A is at least an order of magnitude less than the current from a capacitive-discharge welding setup, but I’m hoping that with some tweaking I can get enough heat to make it all work out. If not, it’ll still be a king-hell resistance soldering setup.

AA Cell Center Contact Electrode

The center electrode started life as an oil-burner ignition electrode. It’s a steel shaft joined to a (most likely) tungsten probe within the ceramic insulating tube. The cable goes off to the other transformer terminal.

Center Electrode – Side Detail

Tungsten is a fairly crappy conductor, so I forged a copper clamp around the end of the electrode. It started as a section of the same copper pipe that went into the pliers, hammered around the wire. That took many annealing cycles, which basically consists of heating the copper red-hot with a propane torch and letting it cool for a bit.

The two smaller screws apply clamping pressure to the copper around the electrode, which ought to improve the contact area. I plan to anneal the clamping area one more time, scrubulate the inside of the clamp, then screw everything together nice & tight with maybe a bit of anti-oxidation compound in there for good measure.

Center Electrode – Front Detail

The general idea is to apply the current as close to the AA cell’s terminal as I can. I think I must file / grind down the end of the probe so that it’s applying the juice exactly to the center of the nickel strip at the middle of the terminal.

The first test was 500 ms at 100% duty cycle, which produced a nice spatter of sparks from underneath the strip, the tungsten glowed orange, but the 8 mil nickel strip didn’t weld itself to the cell top. No weld nugget. Bupkis.

I think it’s got potential, though.

2009-08-23
Slitting Copper Sheet
Slitting Copper Jaws

I’m kludging up a clamp to grab AA cells around their positive terminal so that I can resistance-weld nickel strips to that button. The general idea is that the current passes through the strip, through the button, and out the side to the clamp, rather than trying to heat the button through the strip from the top.

Trial Fitting the Jaws

A snap-ring pliers has pretty nearly all the right attributes, so I’m making up a set of copper jaws with a hole in the middle to grab the terminal. Basically, I whacked off a ring from a copper pipe, hacksawed it lengthwise, hammered it flat (work-hardening it in the process), and drilled some holes.

Then I grabbed it in the Sherline vise and set up a teeny 4-mil slitting saw. A bit of manual CNC ran the saw past the copper and, after a while, the top half just fell over dead with a perfectly shiny cut right down the middle!

Slitting Success

Useful things to remember for the next time around:
- Cut only 0.2 mm into the copper per pass
- 100 mm/min feed is fine
- 4000 rpm is fast enough
- A drop of cutting lube is a bunch on this scale
This worked out a whole lot better than I expected…
2009-08-21
Tour Easy: Easy Reacher Underseat Rack Modifications

Easy Reacher Underseat Rack Improvements

As mentioned there, I have a pair of ERRC’s Easy Reacher underseat packs. They’re supported by an Easy Reacher rack that’s specifically designed for Tour Easy bikes.

Perhaps because I carry dense stuff in the packs, they tend to flop side-to-side. I added a rear strut across the bike frame and a pair of lengthwise plastic (acrylic?) struts to stabilize the packs.

A pair of padded clamps holds the crosswise strut to the bike frame and a washer captures the rear fender’s mounting bracket.

Looks hideous, works fine.

The black tit hanging down from the strut clamp is a bit of heatshrink tubing that cushions the kickstand when it’s up; otherwise, it rattles against the stub end of the aluminum rod.

Yeah, the bike’s pretty grubby. I’d rather ride it than wash it… and, anyway, I follow my father’s advice: “If you have to move it to clean behind it, don’t move it!“

2009-08-20
Tour Easy: ERRC Easy Reacher Pack Repairs

Grocery Hauling Setup

I have a pair of underseat packs on my Tour Easy that have sagged rather badly over the years. That might have something to do with the fact that my toolkit and other odds & ends weighs more than some bike frames; while I don’t need that stuff very often, it’s good to have around.

Tools & suchlike live in the left-side pack, the near one in the photo, and you can see the problem. The right-side pack holds HT batteries, my belt pack, and other relatively lightweight stuff; I’ll fix that one when I see whether this works. The panniers at the rear wheel are for groceries and other bulky items. The trailer, well, that’s how we do groceries…

Broken Pack Backplate

Anyway, the underseat packs have a black plastic (styrene?) backing that cracked under the stress of the stuff inside, allowing the top corners to cave in and the bottom to droop.

The hooks holding the pack to the underseat rack were riveted through the backing sheet and the hardware, but a couple of good shots with a punch broke them free.

Some rummaging in the Parts Heap turned up a big acrylic sheet (“100 times stronger than glass!”) that’s absolutely the wrong material for the job: it’s too brittle. However, I’d like to see whether a stiff backplate will solve the problem or if I’m going to have to get ambitious and build an internal pack frame.

Acrylic Plate and Aluminum Stiffener

It’s essentially impossible to get a picture of a project built largely from acrylic sheet, but here goes.

I traced the outline of the old backplate onto the new sheet’s protective paper, introduced it to Mr Belt Sander to get those nice round corners, then drilled the holes. It turns out to not be quite symmetric, so there’s a right way and a wrong way to insert it into the pack.

All the hardware is stainless steel. They used aluminum rivets, which is the only reason I could punch them out without too much difficulty, that I’m replacing with SS 10-32 machine screws & nuts.

The aluminum stiffener is a random chunk of ribbed extrusion from the Heap; the original was almost exactly twice as long as one backplate, so the two halves (one for the other pack) are precisely right. I milled out the center rib around the nuts to get enough clearance for a nut driver.

Stiffener Hardware Detail

Herewith, a closeup of the hardware. There’s an acrylic sheet in there, honest, it’s under the aluminum extrusion and fender washer. Really!

I put an automobile license plate in the bottom of each underseat pack to act as a floor for all the crap inside; it’s an almost perfect fit and should give you an idea of the pack’s size. It also maintains the bottom’s rectangular shape and keeps heavy stuff from sagging; there’s a hole scuffed in the bottom from the intersection of a high curb and just such an oversight.

Tour Easy Underseat Pack Detail

Having washed the pack while it was apart (there’s a first time for everything), it looks a lot better than it did before. The yellow block in the front pocket is the kickstand plate mentioned there. It used to have a mesh pocket along the side, too, but that snagged on something and got pretty well ripped, so Mary trimmed it off when she sewed a patch over the aforementioned hole.

It’s still saggy, but the top corners of the plate are holding it up a lot better now. If they crack again, I might just have to go with some aluminum sheet.

These packs seem to be obsolete. The ERRC Lloonngg panniers (search for them) seem to be, well, too long for most purposes; they look as though they would interfere with ordinary rack packs. If I were doing it over, I’d look into hacking a pair of smallish duffel bags.

2009-08-19
Front Derailleur Cable Breakage: Round Two

Shift at Small Chainring

This cable guide / pulley may work better than the one described there, because it puts the cable a bit closer to the original location.

To recap, the problem is that the cable bends around the small finger at about 8 o’clock on the derailleur arm. After a few zillion shifts, the concentration of stress at that point breaks the cable, strand by strand, until it snaps at the most inconvenient moment.

The small brass disk (about 0.43″ dia) has a groove machined around the perimeter that’s roughly the size of the shifter cable. The hole (Number 8 or 9 drill) is a slip fit for the 5 mm bolts, but it’s off-center enough that the cable passes roughly where it would without the disk.

A notch in the side of the disk rests on the finger, guiding the cable over the finger without (I hope) bending it at that point.

The cable just wraps around the screw under the original stainless-steel washer, which pretty much crushes the poor thing flat.

Shift at Large Chainring

Here’s another look with the derailleur pretty much over the large chainring. You can see the disk and groove in action.

This was another quick-and-dirty lathe project, with everything done to eyeballometric accuracy. If it works better than the previous half-assed effort, I might actually get around to making a third one and recording the dimensions.

2009-08-17
Mini Razor Knife: Adding a Lock-shut Notch

Mini Razor Knife

I added a miniature razor knife to my belt pack a while ago and was struck by the fact that the blade didn’t lock shut. While having it pop completely open is unlikely, just the thought of a razor blade sliding around next to my hip was unsettling.

But that’s easy to fix…

Blade closed in notch

With the knife closed, use a carbide scriber to mark the blade holder at the end of the locking lever that extends across the back of the knife. You’ll be grinding / filing a notch in the blade holder behind that, just large enough for the locking cam to snap into when the blade is closed. The only vital measurement is the line you just scribed.

Lock the blade holder open, then remove the sharp blade before you do something truly stupid.

Unscrew the Torx-06 screw that holds the locking lever in place, then remove the lever. It’s spring-loaded and will probably bind on the screw, so display some adaptability.

Knife parts

Use a pin spanner to unscrew the blade pivot bolt from the front panel of the knife; hold the corresponding rear nut in position with another spanner or just jam a screwdriver blade into one of the notches. Pretty much everything falls apart at that point, although you may have to do some wiggly-jiggly to get the blade holder out. The washer seems to be swaged into the blade holder hole on my knife, which may be poor production QC.

Using a file or a Dremel-class grinder, gnaw a notch into the back of the blade holder that just barely accepts the cam on the locking lever. This will probably take a few trial assemblies to get right; the notch on mine is slightly too long on the body side (left in the pix), which is OK because the blade holder doesn’t pivot in that direction. If you go beyond the line you scribed earlier (to the right in the pix), the blade holder can pivot open just slightly… and it turns out that the point of the razor blade isn’t all that far inside the knife body.

Notch detail

Anyhow, here’s a detail of the notch. It’s not nearly as pretty as the notch on the other side of the hole that locks the blade open, but it works just fine.

When you get everything back together, the blade holder should snap into the new notch when you close the blade. To open the knife, press down on the far end of the locking lever to pull the cam out of the notch, open it as usual, and the cam should snap into the old notch to hold the blade open as usual.

I keep the goofy plastic safety dingus on the blade anyway, being a belt-and-suspenders kind of guy about that sort of thing.

For what it’s worth, you can’t get into concerts with one of these in your belt pack… for well and good reason, I suppose. They let me hotfoot it back to the van, rather than confiscate it, which is probably one benefit of being an Olde Farte.

2009-08-16
Tour Easy Zzipper Fairing Wrappers: “Bubble Wrap”

Tour Easy Zzipper Fairing Wrappers

We spent four days biking along the Pine Creek Valley rail trail with a Rails-to-Trails Conservancy group ride on our Tour Easy recumbent bikes. Because a crushed-stone path creates a lot of noise that the fairings direct right into our ears and because we weren’t going very fast, we left the fairings at home. As a result, the bikes were wonderfully quiet.

Some years ago, Mary sewed up “bubble wraps” to store our fairings on those rare occasions when they’re not on the bikes. She had some red flannel left over from another project and a hank of cheery Christmas-themed edging, so they turned out to be rather conspicuous.

The trick is to get the size right when the fairing is rolled up. With the fairing in its natural bubble shape, the wrap is rather limp, so you need pockets on both ends to hold the wrap in place. The toes are, she admits, an affectation, but didn’t take much figuring to get right. The width is just slightly more than the fairing’s flat width; you find that by rolling it up and measuring the roll.

She actually made a paper template first to sort out all the curves, then transferred that to the flannel for final cutting.

Tuck in the fairing’s head & toes, roll it up toes first, tie the (attached) strap in a neat bow, and it’s done!

We have three fairings and they roll up together, each in its own wrap, into one tidy, albeit rather heavy, package.

2009-08-07