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

Kenmore Model 158: Needle Lights, Now With Moah LEDs

The first pass at retrofitting SMD LEDs to light the needle area in Mary’s Model 158 sewing machine worked well enough:

Kenmore 158 Needle Light – heatsink

However, she wanted more light on the right side of the needle, so now she has it:

Needle LEDs – front

That’s without any LEDs along the front and back of the arm, hence the dark pool beyond the sewing machine’s base.

Those are the same 5050 warm white LEDs I used on the other side:

Needle LEDs – lower right

Seen without the glare:

Needle LEDs – bottom

They’re mounted on a 32 mil brass strip from the shimstock stash, carefully hand-bent and twisted to match the curvature of the arm, and held in place with JB Kwik steel-filled epoxy for good heat conduction to the aluminum arm. One can argue with the epoxy oozing out from under the brass, but it’s invisible from above.

No construction photos, alas, because I made this in a white-hot frenzy one afternoon and managed to not take any pix during the entire session. Call it working in the flow, OK?

All four SMD LEDs sit in epoxy blobs that isolate them from the brass strip, with 26 AWG solid wire “bus bars” soldered to the top of their terminals and a length of that lovely PTFE-insulated miniature coax leading off into the endcap. More epoxy encloses all the wiring & connections to provide a surprisingly smooth surface that shouldn’t snag the fabric.

The power supply uses an 18 W 120 VAC to 12 VDC brick intended for small LED installations:

Needle LEDs power supply – exterior

The AC comes from the same zip cord that formerly supplied the original 15 W incandescent bulb in the endcap, so the new lights behave the same way: push the power button to turn on the machine and the LEDs pop on just like they should. I put quick-disconnect terminals in the AC line to make it removable, although those need some sort of insulated plug to cover the exposed blades inside their housing.

Inside the black box, a small boost supply steps the voltage up to just under the nominal operating level of 21 VDC:

Needle LEDs power supply – interior

You can just see the adjusting screw hole in front of the AC brick in the overall view.

The DC output exits in the middle of the far side, through a coax jack epoxied to the base.

As before, all six LEDs run in parallel at (for now) 18.5 VDC and maybe 50 mA each, for a total of 300 mA, and seem fearsomely bright even at that. We can now tune for best light as needed.

This is a major major major improvement over the previous tangle of wires stuck on the outside of the machine, with all the wiring internal to the arm and the power supply out of sight under the sewing table.

After an hour, the arm above the four LEDs runs 13 °C above ambient and the endcap over the two LED heatsink is 6 °C over ambient. The AC supply runs at 104 °C and its plastic case offers no provision for heatsinking. All in all, things are warm and not hazardous.

I haven’t retrofit this machine with LED strips along the front & back of the arm, as those may not be needed with the intense needle lighting; the NisLite desk lamp may suffice for area illumination.

2016-08-23
FG085 Function Generator

The topic of function generators came up at Squidwrench a while ago (Sophi was tinkering with LCD shutters) and I finally picked up one of those JYE Tech FG085 DDS function generators to see how they work:

FG085 Fn Gen – in case

Short answer: adequate, if you’re not too fussy.

The board arrived with a bizarre solder defect. It seems a solder stalk yanked one terminal off a ceramic SMD caps:

FG085 – Solder stalk – C26

The schematic and adjacent parts suggested the victim was a 10 uF cap, so I replaced it with one from my stash that worked fine.

However, after soldering enough of the switches to do something useful, the board wouldn’t power up. With a bit of poking around, I discovered the power jack had +15 V from the wall wart, but the center terminals on the DPDT power switch that should have been connected to the jack showed maybe 0.3 V. Jumpering around the failed via and a short trace on the bottom surface let the board power up correctly:

FG085 – Jumpered power trace

If you’re building one of these, solder one pin of each switch, push all the switch caps in place, shove the faceplate over all of them, tape it to the PCB, make sure all the switches are push-able, then solder the remainder of the switch pins. If you do them one by one, you’re certain to end up with a few mis-aligned switches that will either prevent the faceplate from sliding over them or wedge firmly against the side of their assigned hole. Just sayin’.

It lives in a case from Thingiverse:

FG085enclosure – 1268379

I tweaked the dimensions slightly to fit the (slightly larger, possibly new, maybe tolerance-eased) front panel, but the bottom mounting screw hole spacing depends on the front panel size, not a specific set of dimensions, leading me to relocate those holes by abrasive adjustment. I didn’t bother with the lid (which doesn’t clear the BNC jack anyway) or the printed plastic feet (having a supply of silicone rubber feet).

The fancy vent gridwork along the sides printed surprisingly well, even in PETG. I’d have gone with larger slots, although I doubt the thing really needs vents in the first place.

The DDS sine wave output is rough, to say the least:

FG085 Fn Gen – 60 kHz sine

The spectrum shows oodles of harmonic content:

FG085 Fn Gen – 60 kHz sine – spectrum

A closer look:

FG085 Fn Gen – 60 kHz sine – spectrum – detail

Stepping back a bit shows harmonics of (and around) the 2.5 MHz DDS sampling frequency:

FG085 Fn Gen – 60 kHz sine – spectrum – 10 MHz

For comparison, my old Fordham FG-801 analog function generator has nice smooth harmonics:

FG-801 Fn Gen – 60 kHz sine – spectrum

Closer in:

FG-801 Fn Gen – 60 kHz sine – spectrum – detail

Of course, that crusty old analog dial doesn’t provide nearly the set-ability of a nice digital display.

2016-08-19
External Li-Ion Pack: More Sawing

Two of the external Li-Ion battery packs I’m using with the bike radios seemed to fail quickly after being charged, so I sawed them open to check the state of the cells. This time I used the fine-tooth cutoff blades, rather than a coarse slitting saw:

Li-Ion pack – sawing case

As before, a 2 mm depth-of-cut, done 0.25 mm per pass after the first millimeter, seems about right. I didn’t saw the front of the case near the jack, which proved to be a mistake; the interlocked case halves need cutting.

No cell trouble found, which leads me to suspect an intermittent short in the battery-to-radio cable that trips the battery protection circuit. The spare cables went into hiding during the shop cleanout, so I can’t swap in a known-good cable just yet; of course, the existing cable behaves perfectly on the bench. The suspect cable is now on my bike and, if the problem follows the cable, further surgery will be in order.

For the record, the insides look like this:

Li-Ion pack – interior

The cell label seems to show a 2004 date code:

Li-Ion pack – cell label

Given that I got them on closeout in early 2010, it definitely isn’t 2014.

Unlike some of the other cheap batteries around here, they’ve been spectacularly successful!

2016-08-17
Michelin Protek Max Tubes
Within the space of four days, we had three rear-tire flats:
- A tire liner wear-through, after which I didn’t replace the liner
- Four miles later, a blowout through a tread gash previously covered by the tire liner
- A puncture flat directly through the tread
Basically, erosion from the (last remaining, I think) liner in the rear tire of Mary’s bike caused the first flat; I patched the tube and didn’t notice the gash. After the blowout, I patched the tube again, booted the gash (with a snippet from a roll of PET bottle plastic I carry around for exactly that purpose), stuck an ordinary patch atop the boot to cover its edges, and the whole mess has held air just fine for the last week. I’m reluctant to mess with success.

Not having a tire liner caused the third flat, this time on my bike. The wound looked like a nail or glass shard punched directly through the Kevlar armor behind the tread. Fortunately, it happened (or, more exactly, I realized I had a flat) half a mile from home, so I fired a CO₂ cartridge into the tube and pedaled like crazy, which got me halfway to the goal and I rolled the rest of the way on a dead-flat tire.

Ya can’t win.

So I picked up a pair of Michelin Protek Max tubes, the weirdest things I’ve ever stuffed into a bike tire:

Michelin Protek Max Tube – carton

The bumps along the tread surface are much larger and uglier than shown in that picture:

Michelin Protek Max tube

The rubber forming the protrusions has the same thickness as the rest of the tube, so you’re looking at soft, flexible shapes, rather than thick bumps.

The “liquid” inside must be a thin film over the inner surface. I’ve never been a big fan of tire sealants, mostly because they’re reputed to ooze to the bottom of the tire into off-balance puddles.

For future reference, the Official Quasi-Instruction Manual / Blurb (clicky for more dots):

Michelin Protek Max Tube – instructions

We’ll see how well these work…
2016-08-14
LF Loop Antenna: Joint Soldering

Given five meters of 40 conductor ribbon cable, the object is to make a 40 turn five foot diameter loop antenna by soldering the ends together with a slight offset. After squaring off, marking, and taping the cable ends, I stripped the wires:

LF Loop Antenna – wire stripping

Twirling those little snippets before pulling them off produced nicely twisted wire ends with no few loose strands. Separate the individual wires, wrap with transformer tape to prevent further separation, run a flux pen along the wire ends, tin with solder, repeat on the far end of the cable.

Tape one end to the ceramic tile. Align the other end with a one-wire lateral offset and the stripped sections overlapping, then tape it down. Slide a paper strip between the ends, passing under every other wire, to separate the top pairs from the bottom pairs, then tape the strip in place:

LF Loop Antenna – wire prep

Grab each left wire with a needle point tweezer, forcibly align with the corresponding right wire, touch with the iron, iterate:

LF Loop Antenna – top solder joints

The red wire trailing off to the left will become the center tap.

Slide a strip of the obligatory Kapton tape underneath the finished joints, slobber on enough clear epoxy to bond the insulation on both sides of the joints into a solid mass, squish another strip atop the epoxy, smooth down, wait for curing.

Untape from the tile, flip, re-tape, solder the bottom joints similarly, add Kapton / epoxy / Kapton, and that’s that:

LF Loop Antenna – complete joint

Prudence dictates checking for end-to-end continuity after you finish soldering and before you do the Kapton + epoxy thing, which is where I discovered I had 80 Ω of distributed resistance along 200 meters of cable. A quick check showed 40 Ω at the center tap and 20 Ω at the quarters (the black wires on the left mark those points), so it wasn’t a really crappy joint somewhere in the middle.

The joint and its dangly wires cry out for a 3D printed stiffener which shall remain on the to-do list until I see how the loop tunes up.

2016-08-12

BOB Yak Fender Fracture: Fixed

We agreed that repairing the failed flag ferrule made the trailer much quieter, but it still seemed far more rattly than we remembered. It just had to be the fender, somehow, and eventually this appeared:

BOB Yak Fender Mount - fractures — BOB Yak Fender Mount – fractures

The obviously missing piece of the fender fell out in my hand; the similar chunk just beyond the wire arch fell out after I took the pictures. Yes, the wire has indented the fender.

The arch supports the aluminum fender, with a pair of (flat) steel plates clamping the wire to the fender:

BOB Yak Fender Mount - screw plates and pads — BOB Yak Fender Mount – screw plates and pads

The cardboard scraps show I fixed a rattle in the distant past.

Being aluminum, the fender can’t have a replacement piece brazed in place and, given the compound curves, I wasn’t up for the requisite fancy sheet metal work.

Instead, a bit of math produces a pair of shapes:

BOB Yak Fender Mount - solid model — BOB Yak Fender Mount – solid model

In this case, we know the curve radii, so the chord equation gives the depth of the curve across the (known) width & length of the plates; the maximum of those values sets the additional thickness required for the plates. The curves turn out to be rather steep, given the usual layer thickness and plate sizes, which gives them a weird angular look that absolutely doesn’t matter when pressed firmly against the fender:

BOB Yak Fender Mount - Slic3r preview — BOB Yak Fender Mount – Slic3r preview

The computations required to fit Hilbert Curve surface infill into those small exposed areas took basically forever; given that nobody will ever see them, I used the traditional linear infill pattern. A 15% 3D Honeycomb interior infill turned them into rigid parts.

The notch in the outer plate (top left, seen notch-side-down) accommodates the support wire:

BOB Yak Fender Mount - outer — BOB Yak Fender Mount – outer

The upper surface would look better with chamfered edges, but that’s in the nature of fine tuning. That part must print with its top surface downward: an unsupported (shallow) chamfer would produce horrible surface finish and life is too short for fussing with support. Given the surrounding rust & dings, worrying about aesthetics seems bootless.

The original screws weren’t quite long enough to reach through the plastic plates, so I dipped into my shiny-new assortment of stainless steel socket head cap screws. Although the (uncut) M5x16 screws seem to protrude dangerously far from the inner plate, there’s another inch of air between those screws and the tire tread:

BOB Yak Fender Mount - inner — BOB Yak Fender Mount – inner

Given the increase in bearing area, that part of the fender shouldn’t fracture for another decade or two.

I loves me my M2 3D printer …

The OpenSCAD source code as a GitHub Gist:

	// BOB Yak Fender Mounting Bracket
	// Ed Nisley – KE4ZNU – July 2016

	Layout = "Build"; // Build Fender Rod BlockInner BlockOuter

	//- Extrusion parameters must match reality!
	// Print with 1 shell and 3 solid layers

	ThreadThick = 0.25;
	ThreadWidth = 0.40;

	HoleWindage = 0.3;

	Protrusion = 0.1; // make holes end cleanly

	inch = 25.4;

	//———————-
	// Dimensions

	IR = 0; // radii seem easier to measure here
	OR = 1;
	LENGTH = 2;

	Fender = [25,220,1]; // minor major thickness
	FenderSides = 128;

	FenderRod = [5.0/2,(Fender[IR] + 10),5.0/2]; // support rod dia/2, arch radius, rod dia/2 again

	ChordMajor = Fender[OR] – sqrt(pow(Fender[OR],2) – pow(40,2)/4);
	ChordMinor = Fender[IR] – sqrt(pow(Fender[IR],2) – pow(25,2)/4);
	ChordFit = max(ChordMajor,ChordMinor);

	echo("Chords: ",ChordMajor,ChordMinor,ChordFit);

	BlockInnerOA = [40,25,1 + ChordFit];
	BlockOuterOA = [35,25,2 + ChordFit];

	echo(str("Inner Block: ",BlockInnerOA));
	echo(str("Outer Block: ",BlockOuterOA));

	ScrewOD = 5.0;
	ScrewOC = 20.0;

	NumSides = 6*4;

	//———————-
	// Useful routines

	module PolyCyl(Dia,Height,ForceSides=0) { // based on nophead's polyholes

	Sides = (ForceSides != 0) ? ForceSides : (ceil(Dia) + 2);

	FixDia = Dia / cos(180/Sides);

	cylinder(r=(FixDia + HoleWindage)/2,
	h=Height,
	$fn=Sides);
	}

	module FenderShape() {
	rotate([90,0*180/FenderSides,0])
	rotate_extrude(angle=180,$fn=FenderSides)
	translate([(Fender[OR] – Fender[IR]),0])
	circle(r=Fender[IR],$fn=2*NumSides);
	}

	module RodShape() {
	rotate([90,0*180/FenderSides,0])
	rotate_extrude(angle=180,convexity=2,$fn=FenderSides)
	translate([(FenderRod[OR] – FenderRod[IR]),0])
	circle(r=FenderRod[IR],$fn=NumSides);
	}

	module BlockInner() {
	intersection() {
	difference() {
	linear_extrude(height=BlockInnerOA[LENGTH],convexity=3)
	hull() {
	for (i=[-1,1])
	translate([i*(BlockInnerOA[0]/2 – BlockInnerOA[1]/2),0,0])
	circle(d=BlockInnerOA[1]);
	}
	for (i=[-1,1])
	translate([i*(ScrewOC/2),0,-Protrusion])
	PolyCyl(ScrewOD,2*BlockInnerOA[2],6);
	}
	translate([0,0,(BlockInnerOA[2] – Fender[OR])])
	FenderShape();
	}
	}

	module BlockOuter() {
	difference() {
	linear_extrude(height=BlockOuterOA[LENGTH],convexity=4)
	hull() {
	for (i=[-1,1])
	translate([i*(BlockOuterOA[0]/2 – BlockOuterOA[1]/2),0,0])
	circle(d=BlockOuterOA[1]);
	}
	for (i=[-1,1])
	translate([i*(ScrewOC/2),0,-Protrusion])
	PolyCyl(ScrewOD,2*BlockOuterOA[2],6);
	translate([0,0,(BlockOuterOA[2] – ChordFit + Fender[OR])])
	rotate([180,0,0])
	FenderShape();
	translate([0,0,(FenderRod[OR] – 2*FenderRod[IR])])
	rotate([180,0,90])
	RodShape();
	}
	}

	//- Build things

	if (Layout == "Fender")
	FenderShape();

	if (Layout == "Rod")
	RodShape();

	if (Layout == "BlockInner")
	BlockInner();

	if (Layout == "BlockOuter")
	BlockOuter();

	if (Layout == "Build") {
	translate([0,-BlockInnerOA[0]/2,0])
	BlockInner();
	translate([0,BlockOuterOA[0]/2,0])
	BlockOuter();
	}

view raw BOB Yak Fender Mount.scad hosted with ❤ by GitHub

The original dimension measurement and design doodle:

BOB Yak Fender Mount - doodles — BOB Yak Fender Mount – doodles

2016-08-10

BOB Yak Flag Ferrule Failure

At some point along a recent grocery ride, the top half of the flag mast on the BOB Yak trailer went missing.

We had a general idea of where it happened, but, fortunately, I Have The Technology:

This slideshow requires JavaScript.

The flag and pole ended up just off the road, only slightly the worse for wear. I hadn’t planned on riding two dozen miles on a rather hot and humid summer day, but so it goes.

The lower ferrule chafed away enough of the fiberglass pole that it could slip downward, eventually releasing the upper ferrule:

BOB Yak Flag – ferrule chafing

That split near the end enlarged the pole enough that the ferrule couldn’t slide off, so I contented myself with cross-drilling the whole affair for a 1-72 screw, packing epoxy into the hole, tucking more epoxy up inside the bottom end of the ferrule, then burying the screw and nut:

BOB Yak Flag – reassembled ferrule

While I had it on the bench, I replaced the somewhat shredded fluorescent orange tape just under the flag and added a strip of diagonally striped red-and-white retroreflective tape for an attractive barber-pole appearance.

That should last for a little while longer…

2016-08-09

Category: Machine Shop

Kenmore Model 158: Needle Lights, Now With Moah LEDs

FG085 Function Generator

External Li-Ion Pack: More Sawing

Michelin Protek Max Tubes

LF Loop Antenna: Joint Soldering

BOB Yak Fender Fracture: Fixed

BOB Yak Flag Ferrule Failure