Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
The Terracycle (now T-cycle, for reasons presumably involving the transfer of money) chain return idlers on our Tour Easy bikes developed hardening of their urethane tires:
Terracycle Idler tire – printed vs OEM
Urethane shouldn’t crack like that, but after more than fifteen years, stuff wears out.
The white ring is 95A TPU printed on the Makergear M2, which is definitely more flexy than the original tire, but has the redeeming feature of being both Good Enough and trivially easy to model:
include <BOSL2/std.scad>
NumSides = 4*3*2*4;
$fn=NumSides;
Thick = 3.5;
ID = 46.4;
OD = ID + 2*Thick;
Length = 11.2;
tube(Length,id=ID,od=OD,anchor=BOTTOM);
It printed with 5 mm brims on both the ID and OD, because TPU has the barest adhesion to the M2’s glass plate + hair glue. There’s a long-unopened box now on the bench with a BuildTak PEI surface (thank you: you know who you are!) that should improve the situation.
In any event, the tires fit well:
Terracycle Idler tire – installed
The layer-to-layer adhesion isn’t as good as I think it should be, so I’ll likely use those tires as testcases for tweaking the new build plate & settings.
A colony of Yellowjacket wasps moved into a gap somewhere inside our front door, which we noticed only after they set up a heavy traffic pattern over the front step. The nest is far enough up inside the door frame (or, shudder, the wall) to be immune to rattlecan insecticide spray and the wasps simply tiptoe across sticky-trap sheets laid on their entrance paths.
That’s a hulking 12 V electronics case fan mounted on a cardboard bulkhead inside what’s basically a tunnel, with its power supply plugged into a widowmaker extension cord screwed into the light fixture next to the door.
The fan blows away from the door, with the general idea of killing wasps leaving the nest. Arriving wasps can walk home around the box, but departing wasps always take flight from the small crack under the door sill, whereupon they’re sucked into the fan, shattered by the blades, and blown out onto the step.
A Yellowjacket can make headway into a 1 m/s wind, but not for very long, which explains why most of them prefer walking home.
The carnage looks awful, so it seems to be working …
Having just replaced the shower faucet cartridge, the knob insert (probably from 1998, according to a label on the shower stall) could also use some improvement:
Delta 1400 Shower Faucet knob insert – front
That oblong blue tint is water. The shattered sections formerly had small fingers holding the insert into the knob:
Delta 1400 Shower Faucet knob insert – rear
Pry the aluminum disk out of the insert and scan it:
Delta Shower Faucet – label scan
There is no feature in the knob to capture the semicircular notch at the arrow tip, so the disk can rotate as it pleases. I think the arrow should point to the OFF label on the bezel when the water is turned off, but who knows?
Import it into Inkscape, whereupon it becomes obvious the printed legend is not centered on the disk, lay suitable construction lines & circles, then draw similar shapes:
Delta Shower Faucet – Inkscape layout
I located the circles at the Inkscape page corner to put their center at the (0,0) origin with the arrow pointed along the X axis to simplify importing it into OpenSCAD.
The three useful graphic features go on separate layers so OpenSCAD can treat them as separate objects:
The KnobAngle rotation comes from the angle of the features inside the knob that locate the insert, which are aligned horizontally here, but at about 30° when the knob is installed on the faucet :
Delta 1400 Shower Faucet knob – insert recess features
The knob shined up surprisingly well for being three decades old; that photo is as-found.
Import the Inkscape graphics into OpenSCAD and align them an itsy above the top of the insert structure to prevent Z fighting without triggering the slicer into adding another layer:
Those three shapes must be handled separately, lest OpenSCAD combine them into one thing that PrusaSlicer won’t recognize as distinct shapes. There’s no need to subtract them from the main insert shape, but getting separate colors to come out right is definitely not straightforward.
Which looks like this, with cheerful colors that need not correspond to the printer filaments:
Delta Shower Faucet Insert – solid model
Normally I have a set of Build transformations to orient the thing for printing, but doing a simple rotation to put the top down on the platform also blows away the separate nature of the graphics.
I use the EIA color code sequence in PrusaSlicer so I can identify the filament number by eye:
Shower Fauce Knob Insert – PrusaSlicer preview
A little while later:
Delta 1400 Shower Faucet knob insert – installed
The insert is a loose fit in the knob, held in place by good double-sided foam tape to the screw securing the knob. I decided to not bother with little fingers, because I loves me some simple removable adhesive action.
Yeah, you can buy an entire replacement knob for ten bucks, but where’s the fun in that?
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However, the desiccant packets for the most recent pair of boxes (intended to simplify changing the desiccant in the collection feeding the MMU3 atop the Prusa MK4 3D printer) produced this:
Polydryer – as-received desiccant
The silica gel in the left cup looks OK-ish, maybe a little dark, but the fresh-from-the-bag beads in the right cup are crying out for regeneration after having adsorbed about all the water vapor they can.
If you were using that silica gel in its original DO NOT EAT bag, where you can’t see what it’s telling you, you might wonder why it wasn’t doing such a great job of drying the box + filament. The same could happen with a bag of non-indicating gel, along the lines of what I was using a decade ago.
So I dumped both in the Needs Rgeneration bottle and filled both meters with 25 g of fresh silica gel.
A long-lost repair finally made it to the top of the list:
Bicycle Mobile – bottom view
The original string had long since rotted out, but everything else was in a plastic bag just waiting for this occasion.
The colorful cylinders are stacks of laser-cut 6 mm disks with a 2 mm hole, held to the wire & string with a tiny dot of high-viscosity cyanoacrylate glue at each end:
Bicycle Mobile – detail
The disks came from acrylic leftovers:
Bicycle Mobile – laser-cut acrylic
The motion you can’t see makes the shiny bikes much more visible out there:
The weight ball had a 2 mm hole filled by a wood plug which I cleaned out piecemeal with a 1.5 mm drill bit in a pin vise; a short length of wood skewer holds the new string in place.
Because the upper arms support more weight, their disk stacks need fewer disks for the same leverage. The original mobile had (at most) four 6 mm chromed plastic balls at each level, so I started with eight 3 mm disks, adjusted the stack length as needed, glued them in place, then removed the surplus disks by crushing them with a Vise-Grip.
The Smell of Molten Projects in the Morning 
