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.
Who’d’a thunk it?
You know how, in those old cartoons, whenever the vultures started landing in nearby trees, that was an indication of trouble ahead for the hero?
The local Turkey Vulture flock has a roost a few miles away and they’re often seen circling in the thermals overhead.
A few years ago I encountered one dismantling a squirrel flapjack on the road:
It’s an ugly job, but somebody’s got to do it…
I’m not sure whether all unit prices must be converted to “per 100 count” or not, but it really doesn’t work out well for CFL bulbs (clicky for more dots):
That’s $549.50 per 100 bulbs, if you can’t make it out.
On the shelf below, however, a single-bulb pack priced out to $979 per 100 count, so the 2-pack is definitely a better deal!
The NYS DOT recently spiffed up Raymond Avenue in Arlington, installing three small diameter rotary intersections and rows of street lights with lenses cunningly contrived to glare directly in your eyes. Why installing black, non-reflectorized bollards two feet away from the travel lane at each crosswalk seemed like a good idea escapes me, too.
Anyhow, it seems one of those streetlights was a bit too close to the corner. The ruts across the top of the picture came from a truck that evidently clipped the pole and neatly fractured the entire aluminum (?) base casting without bending anything else.
Further south, this wall in Wappingers Falls shows why flat-roof building aren’t such a great idea in snow country:
That isn’t a new problem, by the way. Last year it looked like this:
Not much one can do: water goes where it will.
OK, let’s see how well you do on this round…
In the Mysteriously Missing Label category, we find three similar products with only one shelf label. Which one is the better deal?
You might think it’d be the Wal-Mart Equate house brand. In order to find out, you’d have to haul all three offerings down the aisle and around the corner to the price scanner, which would reveal it’s the one on the far left, by a considerable margin. Oddly, that one says “Double Strength” even though it has the same 200 mg dose as the others.
In the Bizarre Units category, we have two very similar products with completely different unit-price units of measure. Seeing as how a “fluid ounce” is a unit of volume and a “pound” is a unit of weight (or, for the pedantic, force), even the dimensions aren’t compatible. Clicky for bigger pictures.
And, just to show that wasn’t a one-off mistake that could happen to anyone, the smaller size containers continue the theme.
Given that nothing in a Wal-Mart store happens by accident, someone was directed to remove two of those three labels and another someone deliberately chose incompatible units.
Of course, anyone I’ve ever asked has no idea why that would happen…
Having built cartridge heater mounting blocks, I autopsied the two aluminum-case power resistors I’d been using on the MK5 Thermal Core. They weren’t dead yet, but I have some spares in case the cartridge heaters don’t work out as expected.
First observation: the blue-tinted thermal compound I’d put under the resistors turned white! It has a 200 °C maximum rating, so it’s been cooked well beyond any reasonable limit. On the other paw, it was still soft and didn’t have any air bubbles; the resistors were pretty firmly glued in place.
Based on those thermal measurements, I had replaced the original parallel-connected 5 Ω resistors with series-connected 2 Ω resistors, thus reducing the power dissipation in each resistor from 28.8 W to 18 W. While that’s still far beyond the specification, every little bit of reduction helps.
In round numbers, the resistors ran at 50-75% duty cycle to maintain Thermal Core temperatures in the 200-230 °C range. I guesstimate I had 10-15 power-on hours on the resistors, but that may be a lowball estimate: time passes quickly when you’re having fun.
Anyhow, I slipped a brass tube around one resistor terminal, braced the other end on the drill press vise, and pressed the cores out.
The top core literally fell out without any urging, which means that it had shrunk and separated from the housing. That means the resistor was well on its way to failing: a loose core gets hotter and deteriorates faster.
The bottom core was still firmly attached and disintegrated as I forced it out, which means it was in good condition. Paradoxically, the crumbled resistor core in the picture came from the resistor in the best shape.
Given that I ran these resistors at 63% of the original power level, the fact that one was well on its way to heat death after only (at most) a few tens of hours suggests that you shouldn’t expect much life from the stock MK5 resistors. If you haven’t already done so, electrically isolate the thermocouple bead from the Thermal Core to protect the Extruder Controller.
I’m unwilling to sacrifice a new resistor to see if that discoloration is normal, but I suspect it’s not. The ends should be the coolest part of the resistor, which means the middle is discolored, but that picture suggests the opposite, so I really don’t know.
I’d hoped the ID of the resistor bodies would match the OD of the cartridge heaters. That didn’t work out: 0.275 vs 0.250. They’re also a bit too short. If the match was closer, I could see slipping a shim in there, but having two air gaps around the heater just doesn’t make any sense at all.
One of my Shop Assistant’s friends asked for help with a Science Project: building a trumpet-like musical instrument from some sort of tubing. We adjourned the meeting to the local Big Box home supply store, measured various options, and returned with a stock of CPVC pipe and fittings.
Given the budget and physical size of the valves, plus the fact that she planned to make tuning stubs from vinyl tubing, I suggested making all the connectors from fishmouthed sections of the CPVC pipe, which called for a bit of Quality Shop Time before the next build session.
A shell drill is what you use when you want a really big hole all the way through something, so the middle just falls right out. They’re handy for drilling in fragile / delicate material, because the shell supports the material until the drill reaches the far side. They’re also dead simple to make, at least when you’re drilling soft materials, which is pretty much all I do.
I always start by rummaging through the collection to find an existing shell drill that’s close enough to the right size that I can cut it down or bore it out. Here’s the assortment, some of which are obviously victims of previous modifications:
This one was slightly too chubby, with plenty of meat:
That was easy to fix:
While I was at it, I cleaned out the ID to reduce the tooth thickness. That reduces the force applied to the workpiece, which I figured would be a Good Thing considering the size of the pipe.
If you must start from scratch, all you need is a rod that fits inside a tube of some sort: the rod must be chuckable in your drill press and the tube must be about the right diameter for the hole-to-be-drilled. Turn them to suit on the lathe, then press / bash / braze / epoxy / pin them together, paying some attention to concentricity and alignment.
Cross-drill two holes near the business end of the tube, with diameters 1/4 to 1/2 of the tube diameter. Cut off the end to remove about 1/4 of the drilled holes. File some relief on the web between each pair of holes and you’re done.
The holes provide all the rake you could possibly want (take off more of the hole if you need less rake) and filing gives plenty of relief (what you see is grossly too much). None of this is critical for drilling soft stuff; you’ll need more attention to detail in a steel-cuttin’ shell drill.
Then clamp the pipe in the drill press and have at it! The teeth have enough rake that it’ll be grabby, so control the downward force and be sure the vise has a good grip on the pipe.
The trick is to support the pipe by ramming a dowel into its snout from one end or the other, thus preventing the sideways forces from deforming the ever-thinning end. This will take some practice, so buy a spare length of pipe.
After some of that and a bit of cleanup, we had a handful of connectors like these:
Which eventually became the trumpet’s valve assembly:
My Shop Assistant turned wood dowels to a slip fit in the pipe, we drilled suitable holes and Dremeled passageways to convert the dowels into pistons, and it actually worked pretty well. Not nearly as resonant as a brass trumpet, but that wasn’t the design objective.
Haven’t heard how they fared in the competition, but it was a fun project!
So I finally noticed that the water wasn’t nearly as soft as it used to be, which usually means I forgot to dump a bag of salt in the tank. This time, the water was halfway up the tank, which usually means something’s broken.
The usual cause: crud clogging the filter screen upstream of the venturi that sucks brine out of the tank. The usual fix: rinse the screen.
This time, however, the screen was clean. Pulling the gasket off the nozzle assembly revealed a collection of particles and chunks inside the fluidic channels; this is what the gasket looked like after I sorted everything out.
The gasket has at least three layers: a stiff red backing, a compliant green middle layer, and a white surface layer with molded channels matching the red nozzle. The two black cylinders are metering plugs with precisely shaped orifices that control the 0.1 and 0.3 gallon/minute brine and rinse flows.
The green and white layers evidently disintegrated into chunks that blocked the nozzle. With no flow through the venturi, the tank could fill until the float valve limited the flow, but the brining step had a very, very low flow and the resin bed eventually ran out of capacity.
I ordered a replacement nozzle and gasket assembly, figuring that Sears (actually, its OEM supplier) might have changed things in a non-compatible way. The old part numbers, which will get you the new equivalents:
The new parts looked like this:
Surprise! The fancy molded gasket is no more; the replacement is a flat rubber sheet with the appropriate alignment notches and holes. The nozzle assembly might have come out of the same molding machine on the same shift.
I reassembled all the fiddly parts, manually set the softener to its Brine stage, let it suck a few inches of salt water out of the tank, and then returned it to automatic operation. At this point, the water heater is full of hard water and it’ll take a few repetitions of that cycle to get back to normal.
Given the limits of the gasket’s resolution, I’m sure the Batman icon is completely coincidental and sincerely regretted…
The Smell of Molten Projects in the Morning 