Category: Machine Shop

Mechanical widgetry

Rolling Bed Stop

The upstairs Sewing Room came with a couch-like bed incorporating a roll-out trundle bed. It doesn’t get a lot of use, but it lacks wheel locks and tends to scoot away unless you get into it rather more carefully than seems reasonable.

So I made a pair of stops to capture the wheels:

Rolling Bed Stops - installed — Rolling Bed Stops – installed

The solid model shows they’re just plastic blocks minus a model of the roller wheel:

Rolling Bed Stops - solid model - show view — Rolling Bed Stops – solid model – show view

I like the wood-grain effect of the doubly curved recess on printed plastic layers, even if nobody will ever see it:

Rolling Bed Stops - PrusaSlicer — Rolling Bed Stops – PrusaSlicer

The OpenSCAD code also exports a projection of the block as an SVG file to laser-cut the cork pad.

Roll the trundle bed into position, push the stops against the wheels, lift and pull forward an inch, let it down, and the wheels snap into those recesses.

These are considerably fancier than some of the other wheel stops / feet around the house, if only because I got to use the Chord Equation to solve for the radius of the circle parallel to the axle for a snug socket.

The OpenSCAD source code as a GitHub Gist:

	// Rolling Bed roller stops
	// Ed Nisley – KE4ZNU
	// 2025-06-16

	include <BOSL2/std.scad>

	Layout = "Show"; // [Show,Build,Roller,Plan]

	/* [Hidden] */

	HoleWindage = 0.2;
	Protrusion = 0.1;

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

	WallThick = 10.0; // default width for things

	BaseThick = 3.0; // bottom thickness

	RollerOA = [47.2,49.8,40.0]; // min & max dia, length

	FrameClearance = 11.0; // max height under bed frame at roller

	PadOA = [RollerOA[LENGTH] + 2*WallThick,RollerOA[OD],FrameClearance – 1.0];

	//———-
	// Define Shapes

	module Roller() {

	m = (RollerOA[OD] – RollerOA[ID])/2;
	RollerR = (m^2 + (RollerOA[LENGTH]^2)/4) / (2*m);

	up(RollerOA[OD]/2)
	yrot(90)
	rotate_extrude($fa=1)
	intersection() {
	left(RollerR – RollerOA[OD]/2)
	circle(r=RollerR,$fa=1);
	rect([RollerOA[OD]/2,RollerOA[LENGTH] + 2.0],anchor=LEFT);
	}
	}


	module RollerStop() {

	difference() {
	cuboid(PadOA,anchor=BOTTOM,rounding=WallThick/2,except=BOTTOM);
	up(BaseThick)
	Roller();
	}

	}

	//———-
	// Build things

	if (Layout == "Plan") {
	projection(cut=true)
	RollerStop();
	}

	if (Layout == "Roller") {
	Roller();
	}


	if (Layout == "Show") {
	RollerStop();
	color("Green",0.5)
	up(BaseThick)
	Roller();
	}

	if (Layout == "Build") {
	RollerStop();
	}

view raw Rolling Bed Stops.scad hosted with ❤ by GitHub

2025-06-24

PolyDryer Humidity: One More TPU Cycle
With more instrumentation in the PolyDryer TPU box and a day to let the humidity stabilize, the OEM meter reads 24 %RH, as it has all along:

PolyDryer – TPU base – 24pctRH OEM

The indicator cards show the humidity is maybe a little over 10 %RH:

PolyDryer – TPU base – 10pctRH cards

The meter jammed in the other end of the box splits the difference at 15 %RH:

PolyDryer – TPU base – 15pctRH TP

Put the box atop the improved PolyDryer, set it for the recommended 12 hours with “two bars” of oomph (which may roughly correspond to the temperature), and fire it up.

The OEM meter occasionally glitches to 10 %RH:

PolyDryer – TPU dry 1200h – 10pctRH glitch OEM

That type of humidity meter apparently reports values from 10 %RH upward, so this seems like the kind of glitch where the reading jams at one end of the range due to the sensor opening up / shorting / misbehaving. It does not correlate with any nearby electrical activity due to fans / heaters / 3D printers / whatever.

A little under eight hours later, it shows 17 %RH:

PolyDryer – TPU dry 0425h – 17pctRH OEM

Although it still has glitches to 10 %RH.

The cards look about the same, although I could be persuaded the 10% spots look ever so slightly more blue:

PolyDryer – TPU dry 0425h – 10pctRH cards

The meter in the back shows it’s toasty in there:

PolyDryer – TPU dry 0425h – 10pctRH TP

A psychrometric chart shows heating air from 66 °F & 15 %RH to 117 °F will put it at 3 %RH without removing any water vapor. This is far below the level my cheap “instrumentation” can measure, but it does suggest the meters should bottom out, regardless of whatever the silica gel is doing.

Allowing six hours to cool down & stabilize after the PolyDryer turns off in the middle of the night (because for science does not include all-nighters) shows a rebound to 26 %RH on the OEM meter:

PolyDryer – TPU dry 0000h – 26pctRH OEM

The cards remain unchanged:

PolyDryer – TPU dry 0000h – 10pctRH cards

The meter in the back again splits the difference at 16 %RH:

PolyDryer – TPU dry 0000h – 16pctRH TP

I pulled the larger meter and both cards out of the box.

After sitting undisturbed for a day, the OEM meter in the box stabilized at 10 %RH:

PolyDryer – TPU post dry – 10pctRH OEM

The card agrees, to the best of its limited resolution:

PolyDryer – TPU post dry – 10pctRH card

The silica gel weighs 25.0 g, exactly what it did when I loaded the meter case. I think the scale’s 0.1 g resolution exceeds its accuracy, but even if the silica gel weighed 25.2 g ≅ 0.8 % water the humidity would be under 5 %RH.

As far as I can tell:
- The filament on the spool isn’t outgassing water vapor
- The air in the TPU box remains under 15-ish %RH at normal basement temperature
- Running a PolyDryer cycle at 15-ish %RH doesn’t stuff any more water vapor in the silica gel
- Cheap humidity meters lack accuracy around 15-ish %RH
- Humidity meters take longer than you think to stabilize
- Humidity indicating cards may be as good as you (well, I) need
2025-06-23
HQ Sixteen: Under-arm Lights

With the nose ring lights in place, I soldered up eight more 24 V LED strips to light the quilt under the HQ Sixteen’s arm:

HQ Sixteen – under-arm lights – bottom view

A simple fixture aligned the strips for soldering:

HQ Sixteen – under-arm lights – soldering fixture

I intended to peel the masking tape off the glossy cardboard, then use it to keep the strips aligned while I pressed the PSA adhesive on the back of the strips to the machine. The silicone molded over the LEDS turned out to be supremely un-stick-able to the tape and the strips got far more handling than I planned, but I think the adhesive will work.

The cable from the power supply now has a pair of JST SM connectors on the end. Although crimping two conductors into the same pin is not good practice, all 14 of the LED strips draw an aggregate of maybe 130 mA, so I think it’ll suffice.

The JST connectors hide behind the ribbon cable going to the machine’s front panel, so there’s not a lot of basis for arguing they’re unsightly:

HQ Sixteen – under-arm lights – side view

The finished part of the quilt passes under the bottom bar on the left (the rear of the machine table) and forms an ever-increasing roll around the top bar; the white fabric leader attaches to the edge of the quilt. The LED strips illuminate the in-progress part of the quilt under the arm and should be far enough forward to not snag on the rolled-up finished part.

I think there’s now enough light to work with:

HQ Sixteen – under-arm lights – top view

We recently decided the motor stall Heisenbug has vanished, perhaps due to my re-soldering the motor power supply components on the PCB. It’s hard to tell with Heisenbugs, but sometimes they decohere into a desirable state.

After the better part of a year, Mary’s vintage HQ Sixteen runs better than new!

A blog search unearths an extensive project in reverse chronologic order.

2025-06-20
PolyDryer Humidity: Alumina vs. Black PETG

An adjacent pair of PolyDryer boxes have black and orange PETG filament:

PolyDryer – PETG – 27 pctRH Black 25 pctRH Orange

They’ve been sitting closed up for a week or so, with only 25 g of activated alumina in the desiccant holder (no tea bags with additional desiccant) pulling moisture out of their air and, presumably, filament.

The desiccant from the black filament weighed 29.0 g, showing it pulled 4.0 g of water out of the air, 16% of its original weight.

Consulting an old chart of desiccant water adsorption vs. humidity:

Desiccant absorption vs humidity

The “aluminum oxide” curve shows 16% adsorption should correspond to more than 50% RH, so the numbers don’t quite match up. On the other paw, I don’t know how much I can trust the meter accuracy.

I replaced the desiccant with 25 g of silica gel, tucked a humidity indicating card into the box, and snapped it closed again. The orange PETG box also got an indicating card so I can compare results.

2025-06-18
PolyDryer: Noctua Fan Upgrade
The OEM fan inside the PolyDryer is annoyingly loud, even to my deflicted hearing, so I printed a Noctua NF-A4x10 fan adapter and installed a much quieter fan:

PolyDryer – Noctua fan installed

The adapter is upside-down from the suggested orientation, I didn’t bother screwing it to the fan because it has sleeves fitting into the fan screw holes, the slot holds everything together, the vivid green EVA foam sheet sits atop a craft adhesive sheet (both cut with scissors!) ensuring they don’t part company, and it works just fine.

Of course, the OEM fan has a three-wire cable and the Noctua has a four-wire cable:

PolyDryer – OEM vs Noctua fan cables

Although you can’t quite make it out on the white plastic, both connectors have their Pin 1 marks adjacent to each other. I oriented them like that to put the pin release latches on top; a foolish consistency is the hobgoblin of small minds.

Fortunately, Noctua documents their pinout, a bit of probing verified the OEM fan pinout (which does not match the Noctua 3-wire pinout), and the Basement Warehouse Wing emitted an assortment of matching JST XHP connectors. Chop off the black connector and rewire it in a 3-pin XHP connector:
- Pin 1 = OEM Red → Noctua Yellow = +24 V
- Pin 2 = OEM Yellow → Noctua Green = Tachometer
- Pin 3 = OEM Black → Noctua Black = Ground / Common
- unused = Noctua Blue = PWM Speed Control
Which is barely visible plugged into the control PCB on the left:

PolyDryer – Noctua fan wiring

The brown thermocouple wire in the upper right didn’t start out in the notch intended to pass it out of the air flow downwind of the heater:

PolyDryer – crunched thermocouple wire

The wire is exceedingly stiff and requires some persuasion, but it will eventually stay in that slot.

One of the PolyDryer modifications (which I can no longer find) suggested improving the vent openings, because the default slats block more than half of the surface area:

PolyDryer – molded vent slats

I chopped out all but three of the slats and stuffed an arch of aluminum window screen into each recess:

PolyDryer – vent screens installed

Admittedly, it looks a bit raggedy:

PolyDryer – vent screen – detail

As far as I can tell without actually measuring anything, the air flow has increased.

Now, to see how whether all that makes any difference.
2025-06-17
Garden Hose Valve Wrench: Decommissioning

Mary found the wrench I made five years ago in the bottom of her tool bucket:

Hose Valve Knob – five years later

Having moved away from the garden with all the valves that wrench turned, it can now go into the 3D Printed Sample Box for use in the unlikely event I ever give another talk on the subject.

I’d design it differently these days, what with BOSL2 in my sails, but it got the job done.

Some things last long enough!

2025-06-16
HQ Sixteen: Nose Ring Lights Power Supply

With the quilt off the HQ Sixteen, I could install the 24 V power supply for the Nose Ring Lights:

HQ Sixteen Nose Ring Lights – power supply installed

IMO, black nylon screws look spiffier than brass.

The solid model shows the covers have a 2 mm overlap with the power supply case to keep them lined up:

HQ Sixteen Nose Ring Lights – power supply cover – solid model

I managed to reuse three of the five holes from the previous 12 V power supply and drill only three more:

HQ Sixteen Nose Ring Lights – power supply detail

The tops of the power supply ears aren’t quite flat, giving the standoffs a slight tilt that the covers mostly drag back into alignment.

The M4 brass standoffs screw into holes tapped in the thick plastic, thus eliminating nuts inside the power pod:

HQ Sixteen Nose Ring Lights – power supply wiring

The yellow silicone tape wraps two pairs of Wago connectors that dramatically simplify electrical connections in anything with enough space for their chonky bodies.

In the unlikely event you need such things, the original post links the OpenSCAD source code.

With the power supply in place, I think I can put some LED strips under the arm of the machine to light up more of the quilt than the nose lights can reach. More pondering is in order.

2025-06-13