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

  • CPU Heatsink Fuzz Redux

    A friend donated an old Aptiva with an AMD K6 CPU to my collection. It’s too slow & power-hungry to be useful, so I harvested some useful bits and passed the corpse along to the recyclers.

    As fate would have it, I have an upcoming project that needs a cooler, so I popped the fan off the top (it’s rotated a quarter-turn: those tabs lock over the edges of the heatsink) to see what’s inside…

    Fuzz in AMD K6 CPU Cooler
    Fuzz in AMD K6 CPU Cooler

    That accumulation was pretty much invisible from the outside, with most of the fuzz clotted around the periphery of the fan duct. The fan blows downward into the heatsink, which acted (as usual) as a good dust filter.

    A bit of vacuum cleaner work and it’ll be just fine.

    Memo to Self:

    1. The bottom of the heatsink is a 42×78 mm copper block with the heat pipes soldered into notches. Clearance from the block to the step below the widest part of the fins is 18 mm and the fins are 25 mm above the block surface.
    2. Fan = 12 @ 70 mA. Reasonably quiet.
    3. The small blue heat sensor (at about 8 o’clock in the picture) is upstream of the heatsink and, thus, measures ambient air . It’s essentially open-circuit at room temperature, but a diode test shows 1.4 V in either direction. That suggests it’s not a thermistor or thermocouple, but the CPU is old enough that it’s likely not a fancy IC, either. A puzzlement.

  • Arduino Connector & Hole Coordinates: Mega 1280 board

    The Arduino Mega uses the ATMega 1280 chip to get more memory and far more analog & digital & PWM I/O pins, but remains more-or-less header-pin-compatible with the older Duemilanove and Diecimila boards (notes on the header coordinates for those boards is there).

    Arduino Mega - ATmega1280 chip
    Arduino Mega – ATmega1280 chip

    Herewith, some useful coordinates for the Mega board in (X,Y) format using the default 0.001 grid: 1 unit = 0.001 inch (a.k.a 1 mil). Values are taken directly from the Eagle PCB layout.

    The board outline is bounded by (2100,4000) on the upper right, with (0,0) at the lower left by the power jack. It’s not rectangular, but a conversation with Mr Belt Sander could remove the tab sticking out to the right beyond JP1/JP2 if that were really important.

    The header names are not the same as on the old boards. Bolded values seem unusual.

    • PWMH 1×8 @ (1300,2000) ← X is not 1290 as before!
    • PWML 1×8 @ (2150,2000)
    • COMMUNICATION 1×8 @ (3050,2000)
    • JP1 2×8 @ (3750,1550)
    • JP2 2×8 @ (3750,750)
    • POWER 1×6 @ (1550,100)
    • ADCL 1×8 @ (2350,100)
    • ADCH 1×8 @ (3250,100)
    • ICSP 2×3 @ (2555,1100) ← +5 X offset
    • Reset switch @ (2920,1100) ← -30 X offset

    The PWMH header is 10 mils to the right of its position on the older boards, but still not on the same grid used by the other headers: it’s now offset by a nice, even 50 mils. This probably doesn’t matter for most headers, given the sloppy fit. If you have a finicky board setup, you’re in trouble.

    Here’s what the PWMH and PWML headers look like, measured against a Duemilanove board on the top. The offset is not due to perspective!

    Arduino Mega PWMH header offset
    Arduino Mega PWMH header offset

    The Mega board has four 0.125-inch diameter mounting holes (they use 125.984, which is a hard-metric 3.2 mm). The first one is at the same position as on the Duemilanove board.

    • (600,2000)
    • (600,100)
    • (3550,2000)
    • (3800,100)

    Three fiducials:

    • 1 @ (780,2000)
    • 2 @ (2319,1603) ← deliberately offset from the grid?
    • 3 @ (3800,100)

    Memo to Self: As always, verify these numbers before you start drilling!

  • Improved Tour Easy Chain Tensioner

    A discussion on that post reminded me of this old project: replacing the chain pulleys in the midships chain tensioner on my Tour Easy recumbent.

    The problem is that the original pulleys used steel bearings in a plastic race, for reasons that I cannot fathom. They last for a few thousand miles, then get very wobbly and noisy. The solution, as nearly as I can tell, is to replace them with pulleys using cartridge bearings.

    This is what one looks like after four years slung below my bike. Surprisingly, the bearings still feel just fine, even though they’re not really sealed against the weather.

    Tour Easy - Cartridge Bearing Chain Tensioner
    Tour Easy – Cartridge Bearing Chain Tensioner

    Gotcha: the OEM pulleys are not the same OD / number of teeth as pulleys found in rear derailleurs.

    Soooo, after a bit of Quality Shop Time, I had these…

    Tour Easy Replacement Idler Pulley
    Tour Easy Replacement Idler Pulley

    This is where you really want an additive machining process, as I turned most of a big slab of aluminum into swarf while extracting each pulley.

    The first step is to drill holes around the perimeter where the chain rollers will fit, plus drill out as much of the center bore as possible. Then mill down to the finished thickness across the roller holes and helix-mill the bore to size.

    Side 1
    Side 1

    Flip it over and mill the other side to the proper thickness.

    Run it through the bandsaw to chop off all the material beyond the outer diameter.

    Grab what’s left in the three-jaw chuck and mill around the perimeter to get a nice clean edge.

    Side 2
    Side 2

    And then it Just Works. I made another for Mary’s bike, but she said it was too noisy (which is why they used plastic rather than aluminum) and I swapped it for a Terracycle idler.

    This is from back in the Bad Old Days before EMC2’s version of G-Code supported loops. You don’t need to see that code, trust me on this.

  • Banishing a Mysterious Rear-Wheel Squeak

    So the bike started making a weird whistling squeak. Noises on a bike are never a good sign, but it took me nearly two weeks to banish this one…

    Differential diagnosis:

    • Toward the rear: not pedals, not chainring
    • Only while pedaling: not sprocket cluster bearings
    • Depends on chain speed: not sprocket

    Conclusion: it’s the chain.

    My shop assistant had done a massive chain-cleaning and lubricating exercise when we got back from vacation, so I guessed that a few links (of 250-ish) had escaped proper lube. I gave ’em a dose that didn’t help, so I went Old Skool on the thing.

    Coiled it flat in a saucer, immersed it in denatured alcohol to displace air and water-based cleaner inside the links, then drained the alcohol. Poured a generous layer of light machine oil over the whole affair, let it sit for a day. Drained for a pair of rainy days by hanging from a floor joist in the basement. Used up a bunch of rags while wiping the thing down (I have an oily-waste can, they’re not sitting in a wastebasket).

    Misrouted chain in rear derailleur
    Misrouted chain in rear derailleur

    Put it back on the bike, only to discover the chain was now vibrating something awful. Checked the rear end and found that I’d managed to route the chain through the rear derailleur along almost the right path…

    Fixed that and the squeak was still there. OK, it’s not the chain.

    The only remaining possibility: derailleur jockey pulleys.

    Took ’em off without dismounting the derailleur and, lo and behold, the steel-on-plastic bearing surfaces were bone dry and a bit dusty. They’re supposed to be self-lubricating, which is probably true for the first few thousand miles, but I cleaned ’em out and added a dab of grease.

    Problem solved… for a while, at least.

    The only downside is that the chain will be flinging oil for the next month, no matter how often I wipe it down. There’s a good reason I stopped using light machine oil on chains!

  • Silver-Soldering a Stainless Steel Measuring Cup

    Quite some years ago, the spot weld holding half of the handle to the side of my all-time-favorite 1/3-cup measuring cup broke loose. The minuscule weld nugget suggested that the spot welder got distracted; the weld on other side of the handle is perfectly bonded.

    I tried repairing it with silver solder and a torch, which simply proved that’s not within my skill set. I buffed off most of the residue and applied JB Weld epoxy, which lasted just fine until a few days ago. It’s a low-stress situation, indeed, but I’m not surprised that the epoxy didn’t really bond to a slightly scuffed stainless steel surface.

    So, this time around, I did it right: sandpapered off the epoxy, scuffed up the cup and handle by shoe-shining a sandpaper strip face up and face down in the gap, then silver-soldered the handle in place using my resistance soldering gadget (which I promise to describe some day).

    The setup was straightforward. Clamp the cup in the bench vise with soft copper jaws (hammered from ordinary pipe) that also grip one electrode from the soldering unit.

    Silver-soldered handle - left side
    Silver-soldered handle – left side
    Silver-soldered handle - right side
    Silver-soldered handle – right side

    I used a strip of fancy Brownell’s Silvalloy 355 silver solder ribbon (which is 56% silver instead of the chintzy 4% junk I normally use) with some truly toxic silver solder flux. About ten seconds of heat melted the solder and produced a pair of nice fillets along the sides of the handle.

    The flux washed off in hot water and a few licks with fine sandpaper cleaned things up just fine. The carbon electrode left a bit of schmutz on the handle, but nothing a Dremel brass brush wheel couldn’t solve.

    The inside has a bit of heat discoloration, but the sandpaper knocked that back reasonably well, too.

    Heat discoloration inside cup
    Heat discoloration inside cup

    The final product looked a lot better than these in-work pictures, but it’s tough to photograph subtle differences in a shiny silver object.

    Anyhow, as you might expect, we value function over form in this household.

  • Emergency Spoke Repair: FiberFix FTW!

    The rear wheel of my bike popped a spoke while I was riding along a section of unimproved trail trail. Actually, it’d be more accurate to say “as-abandoned” railway line; they ripped out the ties and graded the baby-head ballast more-or-less level. It wasn’t really suitable for a long-wheelbase recumbent bike, but I really hate white-water rafting, which was the other choice.

    Anyhow.

    Of course, the broken spoke was on the sprocket side of the rear wheel. I discovered this when we were out of the most rugged section, so I have no idea how long I’d actually been abusing the wheel.

    I released the rear brake, gingerly rode to the campsite, then installed the FiberFix emergency spoke I’ve been carrying around for a few years. After snugging the cord and tightening the nipple, I added a turn to each of the two adjacent spokes, making the wheel true enough to continue the mission.

    FiberFix spoke in action
    FiberFix spoke in action

    The other end simply passes through the spoke hole in the hub. It doesn’t mind the deformation pressed into the hub.

    Hub end of FIberFix spoke
    Hub end of FIberFix spoke

    Much easier than removing the sprocket cassette under field conditions, that’s for sure!

    Back home in the shop, I installed a new spoke, tightened it up to match the others, backed out the extra turn in the adjacent spokes, and the wheel trued right up.

    I originally built the wheel using a Park Spoke Tension Meter, which is a wonderful tool. If you build wheels, even occasionally, you really, really need one. Lace ’em up, tighten uniformly, then tweak just a little bit for a perfectly true wheel.

    And, yeah, Phil hubs on all three bikes. I hate adjusting bearings. The man is gone; may his legacy live forever.

    Memo to Self: Tension = 23±1 on the drive side.

  • SPD Cleat Backing Plate: Filling the Gap

    SPD cleat backing plate gap filler
    SPD cleat backing plate gap filler

    Mary’s feet are exquisitely sensitive to irregularities in the insoles of her shoes, which poses a real problem with her bike shoes: those SPD cleat recesses are no good at all.

    This is a view down into one shoe, with the SPD cleats adjusted all the way to the rear. That leaves a large recess in the front, which was painfully obvious to her sole. The white shape is the gap filler…

    I pressed a sheet of paper across the gap to get the general shape, traced it twice onto a slab of 0.060-inch aluminum with a nice pebbly paint job, and cut the two pieces out. A few conversations with Mr Belt Sander, a few licks with a rat-tail file, and they dropped right onto place. The recess is slightly curved, but I didn’t have to bend the pieces to fit.

    I laid duct tape across the whole affair, put the insoles back in place, and it was all good.

    The backing plate is 0.072 inch thick and she was content with the difference.

    In previous shoes, with the cleat near the middle of the adjustment range, I’ve stuffed epoxy putty into the gaps. That works, but it doesn’t bond to the (miracle engineering plastic) soles and tends to crumble. This is Not A Good Thing…