Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
I decided to replace the sawed-off flanges on that salvaged heatsink to make all three use the same mounting arrangement, whatever that might turn out to be.
Nothing particularly fancy about it: two random chunks of aluminum sheet and two thinner strips, sanded to roughen their surfaces, and epoxied into place.
The repaired heatsink is marginally taller than its siblings, but not so anybody will ever notice, and it’s no more off-kilter than they are, either.
A quartet of 5/16-inch lathe bits provided the right spacing to hold the heatsink over its new flanges while the epoxy filled in all the gaps and irregularities. I probably should have paid a bit more attention to squaring things up, but it’s good enough for what it’ll need to do.
Y’know how some folks say they don’t wear a seat belt because they want to be thrown free in a crash? Here’s how that works in actual practice.
The air bag fires as the front bumper begins to deform and your body rises off the seat. Because you’re not belted in, the bag boosts your upper torso against the roof liner, bounces your head off the sunshade and bezel, then feeds you directly into the windshield glass.
Laminated glass doesn’t disintegrate, so your skull probably won’t completely penetrate the windshield. You’ll lose some scalp, though, as you slide down the crumbling glass and wedge above the dashboard.
Even if you survive a broken neck, the ensuing brain trauma means you won’t be the same person ever again.
News flash: massive brain trauma does not make you a better person.
Before laminated windshield glass became mandatory, your head would completely penetrate the windshield. Here’s what happened in 1937, from the incomparably grisly — And Sudden Death by J. C. Furnas:
Safety Glass Windshields
I read one of the many Reader’s Digest editions of that article during my formative years. Probably the one in October 1967, if a bit of Google-fu serves me right. You can’t get reprints of it from RD any longer, it seems.
However, unbelievably, while I was composing this post, I checked eBay and found a typewritten copy of the article, signed by Furnas, with 38 minutes remaining in the auction. I was the only bidder: for nine bucks (delivered) it’s mine.
Most likely it’s a publicity / fundraising copy, because the handwritten notation on the first page reads:
With best
regards to
[name]
J. C. Furnas
Oct 20, 1947
Those SUVs reside in the junkyard along the Dutchess Rail Trail near Creek Road, where I might get a new seat to rebuild my comfy office chair this spring.
Found this inside a friend’s dead USB memory stick:
Cold solder joint in USB memory
The leads come from a teeny 12 MHz crystal. The solder blob on the other side looked just fine, but you simply can’t tell by looking.
As it turned out, the stick was dead for some other reason: the Flash memory controller chip got hot when the stick was drawing power. Resoldering all the joints had no effect, which wasn’t surprising.
I suspect a killer static discharge or some such calamity.
I had to drive the old brakes off the mounting studs with a drift punch; the studs were pretty well rusted after a decade of continuous use under the hostile conditions that pass for normal around here. Shined them up, applied a generous layer of Never-Seez, and bolted the new brakes in place.
Turns out that the rear brakes on a Tour Easy are backwards from their orientation on an upright bike: the studs point spinward, so the cable exits on the right side of the frame. Doesn’t make any difference, as that’s how the front brake studs work, but if you’re thinking of buying some fancy brake with odd mounting requirements, you probably shouldn’t.
The installation specs require “more than 39 mm” of cable between the clamp bolt and the bracket on the other arm. The Tour Easy frame tubes are closer together than that, allowing a bare 25 mm of cable.
Rear brake cable and boot
I trimmed the boot to fit, but the real problem is that the arms aren’t at quite the right angle with respect to the braking surface on the rim and provide a bit less leverage than you’d like; the pad alignment is also trickier. I tried adding spacers to the brake pads, but the mounting studs aren’t quite long enough for that.
The first road test indicates the new brakes work much better than the old ones…
Of course, it broke at the first pedal stroke while pushing off across an intersection, which is why I never try to ace out oncoming cars.
This was, mercifully, on the left side of the bike, so I could replace it without removing the rear wheel. Being that sort of bear, I now carry spare screws and we were back on the road in about ten minutes.
A closer look at the head end of the screw shows some interesting details:
Fractured screw – head
The tail end has matching cracks:
Fractured screw – tail
Notice how the cracks are all oriented in the same direction. The screw fractured at the edge of the brazed-on frame fitting, so I suspect the seat stay clamp must be moving just enough to flex the screw across that plane.
I mooched a pair of hardened socket head cap screws from Eks, ground down the head of the right-side screw for better chain clearance around the sprockets, buttered ’em up with Never-Seez, and we’ll see how long Real Steel lasts.
Right-side screw with ground-down head
I really should conjure up a clamp that mounts to the frame tubing, rather than depend on that puny brazed-on fitting, shouldn’t I?
It appears that new Tour Easy ‘bents come with more brazed-on fittings and a more secure seat stay mounting bracket. A photo was there when I looked.
The big one is rated 50 W @ 25 °C ambient. Use two, derated by 50%, times three air-cooled heatsinks for 150 W of low-temperature heating. The little one is 25 W @ 25 °C.
The derating curve is linear from 100% @ 25 °C down to 10% @ 250 °C, when mounted to a square foot of flat aluminum plate: -0.40% / °C.
Assuming a max heater ambient of 150 °F = 65 °C, you can use 84% of full power. Derating by 50% isn’t all that unreasonable.
The relevant hole locations:
50 W: X=1.562 inch / 39.67 mm Y=0.844 inch / 21.44 mm
25 W: X=0.719 inch / 18.26 mm Y=0.781 inch / 19.84 mm
10 W: X=0.562 inch / 14.27 mm Y=0.625 inch / 15.88 mm
Divide those by 2.0 for from-the-center offsets, which may be more useful for manual CNC operations: zero at the resistor mounting center, then back-and-forth from there.
The mounting hole size for 25 & 50 W resistors: 0.125 inch / 3.18 mm diameter, just exactly what you want for a 4-40 mounting screw. Tap drill #43, clearance drill #32 (close fit) or #30 (loose fit).
The mounting hole size for 10 W resistors: 0.094 inch / 2.39 mm to fit a 2-56 screw. Tap drill #50 (better: #49 for 50% threads), clearance drill #43 (close) or #41 (loose).
To get an idea of how those recycled heatsinks performed, I soldered a pair of 8 Ω 25 W power resistors in series, clamped them to the first heatsink out of the dishwasher, fired up a bench power supply, and took some quick data.
Ambient is about 63 °F with more-or-less still air. Temperature measured with an IR non-contact thermometer aimed at a strip of masking tape on the edge of the heatsink. The resistors (and the center of the heatsink) are somewhat hotter than that, as you’d expect. The numbers include the resistor case-to-heatsink thermal coefficient, too.
Held edgewise in a vise with the fins horizontal (like this: ===, the second-worst possible orientation), a few inches above the bench, the temperature stabilizes in about an hour:
16 W -> 101 °F: 2.4 °F/W
32 W -> 132 °F: 2.2 °F/W
64 W -> 188 °F: 2.0 °F/W
The alert reader will note that 64 W is somewhat excessive, given that the resistors are 25 W each. The temptation to run the supply at constant currents of 1.0, 1.4, and 2.0 amps was just impossible to resist, OK?
Heatsink – vertical
Held edgewise with the fins vertical (like this: |||), also with a few inches of clearance to the bench, the temperature stabilized in a matter of 10-20 minutes. I didn’t bother with the lower power tests:
64 W -> 166 °F: 1.6 °F/W
Putting a bare CPU case fan 2 inches from one side of the heatsink, aimed directly at the middle, with no attention whatsoever to ducting or air flow rates, produced a stable temperature in a few minutes:
64 W -> 85 °F: 0.3 °F/W
That’s under 0.2 °C/W with airflow on only one side. Zowie!
While I must run these tests again with the resistors & fans I intend to use (and better control over the air flow), things are looking good.
The Smell of Molten Projects in the Morning 