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.

Month: May 2023

Knitting Stitch Counters: Material Tests

Our Young Engineer knits during rare moments of downtime and sketched an idea for stitch counters to mark progress between those moments. There being nothing like a new project to take one’s mind off all of one’s previous projects:

Stitch Counters – overview

These are more along the lines of feasibility / material tests than finished products, so you’ll see plenty of rough edges.

Prior to doing this, we agreed that 3 mm material was probably too thick, particularly given the small scale: the hexagons are 10 mm edge-to-edge with a 1.5 mm hole for the jump ring.

The jump rings are (mostly) 8 mm OD, which may or may not be the right diameter for all possible knitting needles.

The count sequence goes 10 20 10 40 50 10 with alternating colors:

Stitch Counters – red and blue

Those came from 3 mm red and blue transparent acrylic, looking entirely too much like candy. Cutting two identical layouts from two different materials, then swapping a few counters, gives me two related-but-different sets. This idea is also subject to revision.

I like the set of 3 mm acrylic mirror counters colored with Sharpie:

Stitch Counters – mirror

Alas, the unprotected mirror backing won’t survive long in the real world and Sharpie ink tends to stress-crack the acrylic. Bonding a thin colored sheet / gel filter to the back with an adhesive sheet in between would work, although I don’t look forward to the fiddly alignment. Bonus: sticky edges are a nonstarter in this application.

A setup error produced a set of unmarked counters that might still come in handy for something:

PXL_20230507_150124595 – Stitch Counters – blue blank

Trolase acrylic 1/16 inch = 1.5 mm sheets produce the most visible legends, in a relentlessly industrial sort of way:

Stitch Counters – Trolase

Those have a single thin layer atop a white or black base sheet, but three-layer 1.5 mm Trolase sheets with matching top and bottom colors (cladding on a white core) would look better.

If you can’t decide on a color, go clear:

Stitch Counters – clear

All of those appear on a background of some thin DIY plywood:

Stitch Counters – veneer plywood sheets

The bottom sheet is very pale veneer that came with a layer of genuine 3M 468 transfer tape with 200MP adhesive. I stuck three different veneers on three 100×50 mm rectangles of the stuff to make 1.5 mm thick “plywood”. The adhesive sheet provides lateral strength, not the wood fibers, so it’s not quite as easy to tear as the broken fragment would suggest.

The results look passable, although there’s room for improvement:

Stitch Counters – veneer plywood

After engraving & cutting, I slathered them with clear polyurethane finish and hung them up to dry:

Stitch Counters – wood finish curing

I like the effect, but using the pale veneer for the bottom layer made them look identical from that side. Worse, two of the three top layer veneers had nearly identical colors (one has more grain) after the finish cured.

More thought seems in order, but at least I’ve explored some of the solution space.

2023-05-09
Dirt Devil Stick Vacuum: Floor Brush Salvage

The knuckle joint on the Dirt Devil stick vacuum failed, so it followed us home instead of leaping into the trash:

Dirt Devil – broken swivel joint

Although the fitting seems to be made of ABS, it’s now missing major chunks of plastic in the high-stress areas, so rebuilding it seems not worth the effort.

Because we don’t have any carpets and this one will never leave the basement, I extracted the carpet beater brush and its motor, only to find Yet Another Example of poor assembly practices:

Dirt Devil – stray strands

It’s a 12 V (-ish, I didn’t measure whatever comes out of the vacuum head) DC motor and those errant strands aren’t quite long enough to meet in the middle. The yellow rectangle is a thermal fuse that would be shorted out if the strands were a bit longer.

The broken joint lets the head swivel from side to side, but the elevation joint is still good. If I don’t expect too much, the thing might still suffice for extracting dust from under the benches:

Dirt Devil – taped joint

Worst case, I can swap in a classic floor brush using one of the adapters I made a while ago:

Dirt Devil adapters – assembled

That was easy, if only because I skipped the hard part …

2023-05-08

Bafang vs. Tour Easy: Chain Guide

After adding the Bafang motor to my Tour Easy, the chain has fallen off the chainring a few times, prompting the gap filler between the motor and the chainring spider. That this has never happened to Mary’s essentially identical Tour Easy suggests I have a different shift technique, but adding a chain catcher seemed easier than re-learning shifting:

Chain Catcher - top view — Chain Catcher – top view

It’s more properly called a “chain guide” and is basically a shifter cage minus the mechanism:

Chain Catcher - side view — Chain Catcher – side view

Because the Tour Easy frame has a 25 mm tube where the guide’s clamp expects a minimum 31.8 mm tube, a 3D printed adapter fills the gap:

Chain Catcher adapter ring - solid model — Chain Catcher adapter ring – solid model

The hole is off-center because it seemed like a good idea, although it’s not strictly necessary. The flange helps align the pieces while tightening the clamp screw.

The guide cage clears the chain on all sides while up on the work stand, but there’s nothing like getting out on the road to find out why something doesn’t work as you expect.

The OpenSCAD source code as a GitHub Gist:

	// Chain catcher adapter ring
	// Ed Nisley – KE4ZNU – 2023-05

	/* [Hidden] */

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.2;

	Protrusion = 0.1; // make holes end cleanly

	function IntegerMultiple(Size,Unit) = Unit * ceil(Size / Unit);

	ID = 0;
	OD = 1;
	LENGTH = 2;

	inch = 25.4;

	//———————-
	// Dimensions


	TubeOD = 26.0; // frame tube with silicone tape

	Clamp = [35.0,39.0,12.0]; // Chain catcher clamp ring

	Flange = [Clamp[ID],Clamp[OD],3*ThreadThick];

	Kerf = 1.0;

	Offset = (Clamp[ID] – TubeOD)/2 – 3*ThreadWidth;

	NumSides = 234;

	//———————–

	$fn=NumSides;

	difference() {
	union() {
	cylinder(d=Flange[OD],h=Flange[LENGTH]);
	cylinder(d=Clamp[ID],h=Clamp[LENGTH]+Flange[LENGTH]);
	}

	cube([2Flange[OD],Kerf,3Clamp[LENGTH]],center=true);

	translate([0,Offset,0])
	cylinder(d=TubeOD,h=3*Clamp[LENGTH],center=true);
	}

view raw Chain Catcher adapter ring.scad hosted with ❤ by GitHub

2023-05-05

Bafang Motor: Chain Gap Filler

When the chain falls off the top of the chainring toward the motor, the part remaining engaged with the chainring will inevitably drag the rest into the gap between the motor and the chainring spider, whereupon it will jam firmly in place and be almost impossible to extract. Preventing this means filling the gap, which required several iterations:

Bafang motor gap filler – prototypes

The Bafang motor has a cover held in place by seven M3 flat-head screws, shown here below a test filler using pan head screws:

Bafang motor gap filler – installed

Contrary to what you might think, the five screws that obviously sit on five points of a hexagon do not in fact sit 60° apart. How you find this out is by making the obvious layout, including the two screws bracketing the pinion gear in the lower right, then applying windage:

Bafang motor housing gap filler – hole adjustments

That’s one of the paper templates seen above, with laser-cut holes 60° apart and ugly holes punched at the actual screw locations. Then you scan and overlay that image with the LightBurn layout and twiddle the hole locations to make the answer come out right:

Bafang motor housing gap filler – hole adjustments – LB overlay

With that in hand, I cut a 1 mm acrylic shape to measure the clearance between the motor + filler and the chainring spider, with pan-head screws replacing the original flat-head screws:

Bafang motor gap filler – top view

That’s a single piece of 2.5 mm acrylic I used after discovering a pair of the 1 mm acrylic shapes fit with space to spare: hooray for rapid prototyping.

A test chain drop suggested it might suffice:

Bafang motor gap filler – test

If I were so inclined, 3 mm acrylic with countersunk holes and slightly longer flat-head screws would probably work, but I’ll use this until it fails to prevent a chain snag.

The careful observer will have noted the stress crack extending radially inward from the upper-right screw, which I am carefully avoiding doing anything about, pending the aforementioned failure.

The LightBurn layout as a GitHub Gist:

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view raw Bafang motor housing gap filler.svg hosted with ❤ by GitHub

2023-05-04
Zenni Optical Glasses: Nosepad Misalignment

Mary’s new glasses arrived from halfway around the planet with excruciatingly misaligned nosepads:

Zenni Optical glasses – misangled nosepads

Despite past experience, Zenni generally does better than this.

Fortunately, a few minutes with the same metal-forming pliers as before settled them in place.

Ya gotta have tools!

2023-05-03
Subaru Forest High Beam Bulbs: Thermal Damage

Although these passed the annual New York State safety inspection, I thought they needed replacing:

HB3 9005 Bulbs – bulged glass

A closer look:

HB3 9005 Bulbs – bulged glass – detail

The bulge was upward, of course.

The Forester’s manual says they’re HB3 bulbs, but the rest of the world knows them as 9005 bulbs. At full power they draw 60 W = 5 A each, although we rarely drive at night and then rarely have the opportunity for much high-beam use. I assume the blackening comes from nine years of running at half-ish power as the Forester’s daytime running lights.

The low beam headlights seem to be in fine shape.

These two went into the tray under the floor of the rear cargo area, because the crappy bulb you have is better than the one that just burned out on the road.

2023-05-02
Laser Cutter Z-Axis: Hitch in the Git-Along

My OMTech 60 W laser cutter has a stepper motor Z axis drive that has worked flawlessly since it arrived. However, it recently developed a periodic klonk during autofocusing and manual jogging, loud enough to shake the platform and rattle the cabinet’s bottom plate.

A few minutes of poking around revealed the klonk happened on each turn of the Z axis leadscrews, which quickly led to finding the cause:

Craft Stick – swarf in belt drive

It’s a rectangular wood chip, perfectly sized to jam into the Z axis motor pulley driving the belt: a belt tooth lifts up on the chip as the pulley turns, then klonks as it slips off the other side. The motor pulley and all four leadscrew pinons have the same number of teeth, so they’re all at the same point in their rotation when the belt slams down onto the pulley.

Where might such a thing come from? Well, I recently finished a batch of plant markers and hadn’t yet cleaned out the “chip tray” which is also just the bottom plate of the cabinet:

Craft Stick – swarf

I briefly considered building a guard for the motor pulley, but the belt most likely carried it from elsewhere. The leadscrews have an ample coating of grease that was also smeared elsewhere on the cabinet, making the belt sticky enough to catch such things.

The chip tray is once again pretty clean and the platform behaves normally again.

That was easy …

2023-05-01