Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
So there we were, biking along the northern segment of the Dutchess Rail Trail, when a squirrel scampered up a fencepost a few hundred feet ahead of us and struck a classic tree-rat pose: standing up atop the post, tail arched behind, front paws together.
As we rolled closer, the squirrel noticed us and, as squirrels are wont to do, panicked.
*Must* *run* *away*
Squirrels tend to escape up the nearest tree, which works perfectly with most predators. In this case, though, the squirrel was already as high as it could get on the post and there were no trees within jumping distance.
Decision time: can’t run up, can’t escape to the side, must not run toward the threat.
*Must* *run* *away*
So the critter lit off along the top rail, hurdling over the protruding fenceposts in a dead run, as fast as its little legs could carry it.
Which, as it turned out, was just over 15 mph. We stopped pedaling and coasted, but this section is slightly down-grade and we didn’t slow very much.
The thing was running at my eye level, about five feet to my left, and kept pace with us for maybe a dozen fenceposts. Finally it decided this tactic wasn’t working and dove off the fence into the bushes beside the trail.
Squirrels must produce adrenaline like I produce saliva.
I suppose I should have known better: the bottom of that heatsink wasn’t anywhere near flat. I think it mated directly with the top of the CPU through thermal grease, not a compliant pad.
Curved copper heatsink surface
The obvious solution is to flycut the thing, which is where the Sherline’s limited Y-axis travel and teeny table put a cramp on your style. Normally, you’d put the length of the heatsink parallel to the X axis so the flycutter would clear on both ends, but there’s no obvious (read: quick and easy) way to clamp the thing that way.
So I mounted it parallel to the Y axis, which meant I couldn’t get the flycutter completely off the near end. The first pass at Z=-0.1 mm, however, showed that not only was the surface curved, but it wasn’t parallel to the top of the fins (which were flat on the tooling plate). I suppose I should have expected that.
This cut is has Z=-0.1 mm referred to the front end. It completely missed the other end:
First flycut pass
I flipped the heatsink around, measured the front-to-back tilt (about 0.16 mm), stuck a couple of brass shims under the front, and the second pass at Z=-0.05 mm from the new low point did the trick. Copper is nasty stuff and I did these cuts dry: the chips visible near the front are stuck firmly to the surface.
Final flycut pass
I scrubbed both the heatsink and the spreader plate on some fine sandpaper atop the sacrificial side of my surface plate until they were all good. I can see the remaining flycutter marks, but I can’t feel them, and the plates slap solidly together with a pffff of escaping air:
Flattened heatsink and spreader
A dab of heatsink compound should work wonders; the maximum dissipation will be under 20 W, roughly comparable to that old K6 CPU, but now the heatsink will be contacting the entire hot surface.
Most office desk chairs are crap. Spend a couple of hours in a typical office chair and you wonder if it had been designed by aliens who, perhaps, read the specs for human beings, but never actually met a person in the flesh.
Conversely, you can drive for a couple of hours and get out of the car feeling at least OK. (Well, if you buy a decent car, that is. Last rental car I drove had terrible seats.)
So, a couple of decades ago, I went to a junkyard and picked up a nice seat from a fancy wreck for about $50, built a plywood base with six casters from Home Depot, put a 1-foot-diameter Lazy Susan bearing between the two, and bolted everything together. The seat even had power adjustments, so (just for fun) I tucked a battery underneath.
After a while, I stripped off the seat belt doodads… and, of course, you really don’t need power adjustments after the first week.
Worked like a champ for about a decade, but even a high-end seat cushion eventually goes flat. So I swapped in a front seat salvaged from one of our cars (a Toyota Camry wagon, from back before minivans ruled the road) and that lasted another decade. It finally went flat and I swapped in the other front seat.
The 2×6-inch upright boards have slopes and cutouts that match the peculiar shape of the seat frame, with holes drilled in the wood for the metric machine bolts, and that’s a good enough anchorage for an office environment.
Chair base
The Lazy Susan bearing is between the top plywood layer and the square corner sticking out to the front. That layer bolts to the bottom sheet, providing enough clearance for the various heads and whatnot.
You really need six casters on a fairly large base, because the chair is immensely heavy (it was, after all, designed to not fall apart during a full-on collision) and rather top-and-back-heavy without you in place.
Considerations:
Get the seat close to the right height, as the adjustment range isn’t all that wide
Put your center of gravity in the middle of the base. Fortunately, the seat has plenty of forward-aft adjustment
Get the seat base pretty much horizontal
A closer look at the front:
Front detail
The back isn’t a lot different:
Back detail
Maybe I just have a weird butt or don’t spend enough money on office chairs.
The continuous ink system I have on the Epson R380 occasionally stops the yellow ink flow. I think it’s related to back pressure: the lines drain down quickly after the printer stops and the yellow line is on top.
The label on the front of the continuous ink supply reservoir minces no words:
Do not raise the external ink reservoir higher because of curiosity or insufficient ink-supply …
Well, maybe a little bit won’t hurt?
As it turns out, the original ink tanks inside the printer are pretty high up, with the bottom of the print heads maybe 60 mm off the table. That chunk of foam packing material is 40 mm tall: the bottom of the ink supply remains well below the heads.
The ink supply tubes drain back a few cm when the printer has been idle, which means the elevated reservoir isn’t applying positive pressure to the heads. And, after a few weeks of this treatment, the yellow ink flow hasn’t stopped!
I’ll call it a win.
Here’s the overall view, with a few ink splotches visible from previous blunders. If the table wasn’t a raw slab of half-inch plywood bolted to a surplus printer (?) stand in the basement, I’d care a lot more…
Elevated continuous ink reservoir
The amount of ink in the waste ink tank beside the printer is breathtaking: about 50% more than noted there.
The scrap pile disgorged a chunk of aluminum plate exactly the correct size for a heat spreader that will mate eight power FETS to that heatsink. The catch: a 1-1/4-inch deep hole tapped 1/4-20 for about 3/4 inch at almost the right spot along one end. Rather than sawing off Yet Another Chunk from the original plate, I figured it’d be more useful to just plug the hole.
Note that this is somewhat different than the situation described there, where I screwed up by putting a hole in the wrong place. Here, I’m just being a cheapskate by making a piece of junk good enough to use in a project, rather than having it kick around in the scrap pile for another decade.
Anyway.
I turned a 3/8-inch diameter aluminum rod down to 1/4 inch for the threaded part and a bit under 0.200 inch to fit into the partially threaded end.
A real machinist would single-point the thread, but I just screwed a die over it. The narrow end is slightly larger than the minor thread diameter, which helped get things started. Then a trial fit, saw off the excess on the skinny end, and apply a touch of the file to shape the end to mate with the hole’s drill-point bottom:
Threaded hole plugPlug epoxied in place
I buttered up the plug with a generous helping of JB Weld epoxy and screwed it in. Toward the end of that process, the air trapped in the end became exceedingly compressed, to the extent I had to stop after each quarter-turn to let it ooze outward; eventually the hole gave off a great pffft as the remaining air pooted out. Unscrewed slightly to suck some epoxy back in, screwed it tight, and let it cure overnight.
Squared-up block with plugged hole
Sawed off the plug, filed the rubble more-or-less smooth, then squared it in the Sherline mill. The heatsink prefers to sit on a nice, smooth metal surface, so I flycut the other side of the block to get rid of a few dings and the entire anodized layer while I was at it.
The epoxy ring doesn’t have a uniform width, because you’re looking at a cross section of the thread. The skinny part is the crest of the plug thread, the wide part is along one flank. Barely a Class 1A fit, methinks.
New hole
Locate the midpoint of the block’s end, center-drill, then poke a new #29 hole 20 mm deep (I really do prefer metric!) for an 8-32 screw. The plug didn’t move at all during this process, pretty much as you’d expect. The chips came out of this hole in little crumbles, rather than the long stringy swarf from the solid aluminum on the other end.
Using a simple peck drill canned cycle is just downright wonderful:
G83 Z-20 R1 Q3 F100
The rule of thumb is 3000 RPM with a feed 100 times the drill diameter. In this case, the drill is about 3 mm and calls for 300 mm/min, but the Sherline is happier with slower feeds. Maybe if I was doing production work, I’d push it harder.
A real machinist would have a milling machine with a servo-driven spindle for rigid tapping, but I just screwed an ordinary hand tap into the holes.
A bit of futzing converted a pair of solderless connectors into clips that capture the hooks on the ends of the heatsink’s springy wiffletree to secure the spreader to the heatsink. You can see the flycut surface peeking out from below the end of the heatsink. I should hit it with some fine abrasive to polish it out, but I think heatsink compound alone will do the trick.
Heat spreader on heatsink
The next step: drilling-and-tapping eight more blind holes along the sides for the FETs. It’d be really neat to have a servo spindle…
While walking home with the bike, I noticed that the odometer wasn’t matching up with reality. This generally means the front-wheel magnet sensor got whacked out of line and, given that I’d just laid the bike down on that side, that’s what I expected to fix.
As it turned out, the failure meant it was time for the more-or-less annual contact cleaning. The three tiny contact balls on the bottom of the Cateye Astrale tend to collect enough dirt over the course of a few thousand miles to become intermittent. The balls lead to the wheel and pedal sensors, with a single common wire.
Cateye Astrale contacts
You can see that they’re not shiny little factory-fresh bumps. Here’s a detail of the upper-right one on the base to the right. Even through the horrors of a tight crop from a hand-held shot, you can see the problem.
Cateye Astrale – contact detail
No big deal, just wipe ’em off and apply a bit of DeoxIT to make ’em happy again for another year.
The Smell of Molten Projects in the Morning 