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

PolyDryer Humidity: Meter vs. Indicator Cards vs. Adsorption

A week after installing 25 g of fresh silica gel, without any outside influence other than using some of the filaments to build things, I recorded the humidity meter reading, the indicator card colors, and the weight gain.

Click on any picture for more dots and to get rid of the captions and their stylin’ photo-blur.

White PETG, gain 0.6 g:

Polydryer – 14 pctRH – meter – white PETG

Polydryer – 14 pctRH – card – white PETG

Black PETG, gain 0.8 g:

Polydryer – 21 pctRH – meter – black PETG

Polydryer – 21 pctRH – card – black PETG

Orange PETG, gain 1.0 g:

Polydryer – 14 pctRH – meter – orange PETG

Polydryer – 14 pctRH – card – orange PETG

Blue PETG, gain 0.4 g:

Polydryer – 14 pctRH – meter – blue PETG

Polydryer – 14 pctRH – card – blue PETG

Blue PETG-CF, gain 1.3 g:

Polydryer – 20 pctRH – meter – blue PETG-CF

Polydryer – 20 pctRH – card – blue PETG-CF

Black PETG-CF, gain 2.1 g:

Polydryer – 28 pctRH – meter – black PETG-CF

Polydryer – 28 pctRH – card – black PETG-CF

Gray PETG-CF, gain 2.1 g:

Polydryer – 28 pctRH – meter – gray PETG-CF

Polydryer – 28 pctRH – card – gray PETG-CF

The (newer) indicator cards with the smaller dots / larger black borders seem less acute than the (older) large-dot cards. The two 28 %RH cards look about right, but the 20 and 21 %RH cards seem more different than the similar humidity would suggest.

Under 20 %RH, all the spots look pretty much the same, but AFAICT any humidity below 20 %RH is Good Enough for 3D printing.

The Blue PETG-CF went directly from its sealed bag into the PolyDryer box, unlike the Black and Gray PETG-CF spools that sat in the 50% RH basement long enough to soak up the ambience. The Blue has outgassed enough water to suggest spools do not arrive “bone dry” from the factory, although the Black and Gray prove the Basement Shop is wetter than the factory.

All of the silica gel together weighed 184.2 on the same scale I originally measured the 25 g quantities that should have totalled 175 g, but the individual measurements total 183.3 g. I don’t trust the scale to be better than ±0.1 g on any measurement, so half a percent is likely as good as it gets.

The silica gel weighed 187 g on the kitchen scale, sweated down to 179 g after 7 minutes in the microwave being defrosted like 1.5 pounds of fish, and, depending on which numbers you believe, released 8 to 10 g of water in the process.

Microwaving something containing so little water means the silica gel absorbs very little of the energy: the dish, glass turntable, and metal walls got absurdly hot. I think using the induction cooktop and cast iron pan makes more sense, even if it takes longer.

With fresh silica gel in place, perhaps waiting two weeks will produce interesting numbers.

2025-07-02
Plastic Spring Clamp Jaw Rod Replacement

A recent quilt photo shoot degenerated into me chasing several bright orange clamp jaws across the deck as they popped off their clamps hanging from the photo backdrop scaffold. Most clamps have jaws snapping onto actual rods, but these clamps have molded-in-place “rods” much smaller than the 2 mm expected by the jaws and much more irregular than seems reasonable.

Trace and scan the nose of a clamp:

Large spring clamp nose outline

Curiously, the molded rod is not centered in the nose:

Large spring clamp nose – pin locatIon

Use LightBurn to coerce a scan of the first sketch into a suitable path, laser-cut some MDF, and glue up a drill fixture:

Spring clamp jaw pins – fixture gluing

Align the drill to the center of the off-center hole marked on the bottom layer:

Spring clamp jaw pins – drill alignment

The drilling setup looks casual, but hand-holding the clamps against the rear wall and into the form-fitting nose recess sufficed:

Spring clamp jaw pins – fixture overview

I snipped the plastic “rods” out before drilling the holes, then rammed 2 mm steel rods in place:

Spring clamp jaw pins – steel

They’re really 5/64 inch = 1.98 mm rods from the oil-hardening drill rod stash, but entirely sufficient for the purpose.

With one clamp in hand, though, there was obviously no reason for the rods to be off-center. So I centered the drill in the nose, punctured the rest of the clamps, and pressed 2 mm carbon fiber rods in place:

Spring clamp jaw pins – steel vs carbon fiber

The rods were cut to 20 mm by rolling them across a pad with firm pressure from a utility knife. That was mostly to get some experience cutting carbon fiber, which is obviously overqualified for the job.

Snap the orange jaws in place and I shall never suffer the embarrassment of chasing them again …

2025-07-01
CNC-3018XL: Table Drive Nut Overstress

A confluence of unrelated events led me to unboxing and setting up the CNC-3018XL most recently used to plot Homage Tek Circuit Computer decks, but the table slid along its rods entirely too easily. A peek at the leadscrew revealed an assortment of parts last seen when I extended the frame:

3018CNC – table drive – as found

The featureless cylinder is the leadscrew follower nut, which evidently popped out of its proper place in the table drive block:

3018CNC – table drive parts

The crude chamfer suggests that end went into the block first, so that’s what I did:

3018CNC – table drive – follower nut installed

It seems snug enough in there, at least for a machine used solely for plotting and maybe drag knife cuttery, so I’ll assume the box received some rough handling during our move.

It’s now back in place and seems to work well enough:

3018CNC – table drive – installed

I briefly considered adding some setscrews to hold it in place, but came to my senses. If it pops out again, maybe it’ll be time to rebuild that block with proper retention.

The software side of the thing surely needs TLC, too.

2025-06-30
Activated Alumina Regeneration

Having accumulated a bunch of used activated alumina desiccant, I figured now was a good time to try regenerating it. Industrial applications use dry gas and very high temperatures, but perhaps holding it over 100 °C for a few hours will suffice for my purposes.

I pressed our daily driver cast iron skillet and induction cooktop into service:

Alumina regeneration – induction cooktop

After an hour the surface temperature was around 150 °F, so I covered the pan with a water-cooled lid to see if any vapor condensed on it:

Alumina regeneration – lid cooling

It did, indeed, so I alternated covering and exposing the pan, which was likely a waste of my time, until the alumina dried enough that the lid didn’t collect any condensation. The whole process took just under four hours with the cooktop set to its maximum of 460 °F for most of the time.

The beads then cooled to room temperature in a covered dish:

Alumina regeneration – final cooling

The beads weighed 626 g at the start of the adventure and sweated down to 593 g, parting with 33 g = 1.2 oz of water in the process for a loss of 5.6%. I have no idea how dry they are now, but they’re an ounce drier than before.

2025-06-25

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