Category: Science

If you measure something often enough, it becomes science

PolyDryer Humidity: April-ish

	2026-04-16
Filament	%RH	Weight – g	Wt gain – g	Gain %
PETG White	14	–	–	–
PETG Black	14	–	–	–
PETG Orange	22	52.5	2.5	5.0%
PETG Natural	15	–	–	–
PETG-CF Blue	23	55.4	5.4	10.8%
PETG-CF Gray	18	–	–	–
PETG-CF Black	14	–	–	–
PETG Blue	10	–	–	–
TPU Clear	14	–	–	–
TPU Black	14	–	–	–

Most of the PolyDryer boxes had the same humidity as before, so I didn’t disturb them. When the humidity starts to rise, then we’ll see what’s going on in there.

The PETG Orange meter continues to misbehave and has been glitching from 22% to 30%. The indicator card shows the humidity is around 10% inside and the relatively low weight gain suggests there’s not much water to be adsorbed.

The PETG-CF Blue spool is new and, once again, shows filament does not arrive bone-dry in the factory wrapper.

Those two boxes now have alumina beads.

Dehydrating the jar of wet silica gel on the induction cooktop (set for 405 °F) sweated it down from 532 g to 503 g over the course of four hours, with nearly all of that change in the first two hours.

Obligatory photo from a while ago, because it looks pretty much the same now:

Silica gel beads - drying — Silica gel beads – drying

2026-04-20

Basement Air Filter Box: Ewww!

Late last year I assembled four air filters and a fan quintet into a box filter:

Basement Air Filter Box – installed

Running continuously for three months made the air filters look like this (with an unused filter on top for comparison):

Basement Air Filter Box – 3 months – A

I have not stretched the image contrast, so the new filter isn’t the pure white in the top picture, but it’s still about the same white as the cardboard frame. The floor is, indeed, painted gray.

Looking at the pleats in the other direction to show I’m not making it up:

Basement Air Filter Box – 3 months – B

The inside surface of the filters has the same gray appearance. The fans are, unsurprisingly, immaculate.

Totally did not expect that!

The filters sport a MERV 13 rating and snag “most smoke” from the passing air, so they’ve been collecting any fumes not sucked out of the laser cutter, along with whatever arises from other Basement Shop™ activities.

So I’ll buy another set of filters, build another box, and see what accumulates during the next three months.

2026-04-08
Prusa MK4 Foam Feet: Embiggened

It turns out the Prusa MK4 weighs enough to squish my add-on foam feet to about half their original thickness:

Prusa MK4 Foam Feet – embiggened

The two in the front are 30×30 mm and the shorter (more squished) foot was under the right rear of the MK4 where the power supply lives.

The larger feet (one installed) are 60×60 mm and, with the same weight supported on four times the area, should squish much less.

Stipulated: I can’t hear the difference either way.

This project was precipitated by finding a large scrap of exercise mat foam in a place where it shouldn’t have been.

2026-03-24
Alumina Desiccant: Regeneration Timeline
Having accumulated a suspiciously precise 700 g of activated alumina desiccant from the PolyDryer filament boxes, I poured it into the same cast-iron pan on the induction cooktop:

Alumina regeneration – induction cooktop

Based on the results from last time, I set the temperature to the cooktop’s maximum 460 °F and, bother fiddling with condensing the moisture on a lid, and let it cook.

Weighing the beads (about) once an hour:
- Start: 700 g
- 1 hr: 678 g
- 2 hr: 666 g
- 3 hr: 661 g
The 39 g water loss is 5.6% of the wet weight and 5.9% of the dry weight, which is roughly the amount absorbed by both silica gel and alumina after a month or so in the filament boxes.

During those hours the surface temperature rose from 73 F to 190 °F, although the exact number depends on exactly where the IR thermometer was staring. Stirring the beads to get an average temperature might be more convincing, but not by much.

Exactly how dry the beads become after three hours remains unknown, but the temperature increase suggests most of the water has gone elsewhere.

Cooling the beads in a covered bowl and pouring them into a jug produced a total weight of 767 g, which settled at 770 g over the course of two days; the jug seems reasonably vapor-tight.

Alumina beads seem much less prone to damage by overheating than silica gel beads and have similar performance in the boxes, which makes them a strong contender for the next round.
2026-03-12
LED Garage Light: Autopsy

The hidden part of all three LED arrays in the dead garage light looked like this:

LED Garage Light – inadequate heatsink compound

Although the compound was still gooey, there wasn’t nearly enough of it. The few tendrils on the heatsink suggest the LED array had bowed upward, pulled away from the cast aluminum, and eliminated any direct conduction.

A bit of probing showed each LED array had 16 series groups of 4 parallel LEDS, with one group in each array failed open. That group was toward the end away from the inadequate heatsink compound: the LEDs died from heatstroke brought on by neglect.

The Drawer o’ LED Arrays disgorged a bag of surplus LEDs labeled “10 W 9-12 V 750 mA”:

LED Garage Light – epoxy replacement

It’s sitting on a generous blob of steel-filled JB Kwik epoxy that should do a great job of conducting heat. A bag of cheap constant-current supplies is on order.

Amazon has similar “10 W 9-12 V 350-450 mA” arrays.

Try as I might, I can’t get 10 W from those numbers, but I’ve never understood advertising math.

2026-03-10

Polydryer Humidity: February

After two months of sitting around:

	2026-03-07				2026-03-08
Filament	%RH	Weight – g	Wt gain – g	Gain %	%RH
PETG White	14	53.2	3.2	6.4%	10
PETG Black	14	52.3	2.3	4.6%	14
PETG Orange	24	52.1	2.1	4.2%	32
PETG Natural	18	52.6	2.6	5.2%	14
PETG-CF Blue	18	52.8	2.8	5.6%	14
PETG-CF Gray	18	53.5	3.5	7.0%	14
PETG-CF Black	14	53.2	3.2	6.4%	10
PETG Blue	10	52.5	2.5	5.0%	10
TPU Clear	18	52.7	2.7	5.4%	10
TPU Black	14	53.6	3.6	7.2%	10

The last three boxes had 50 g of activated alumina and got fresh doses from the same bottle.

The other boxes had 50 g from the original bottle of silica gel beads and now have regenerated (and likely damaged) silica gel beads.

AFAICT, the meter in the orange PETG PolyDryer box isn’t working right, because the humidity indicator card in there has blue spots all the way down to 10%, just like the other boxes. Color differences for meter readings in the teens may be too subtle for my eyes.

Next time around, they’ll all get alumina beads.

2026-03-09

Punched Cards: Paper Matters

Using different card colors makes it easy to find your program deck in the Comp Center’s output bins:

Punched Cards – paper color vs smoke stains

The smoke stains on the bottom orange card came from the same LightBurn settings used with the purple (violet?) and blue (teal?) cards: 400 mm/s, 35% power, and assist air enabled.

The conventional wisdom is that you *do not* use assist air while engraving, to avoid pushing the smoke / soot down onto the material, and I’ve generally followed that rule. Apparently evaporating holes in the other colors doesn’t generate much smoke and I had no reason to notice the air was enabled.

The upper orange card differs from the lower one only in having the assist air turned off, so I have definitely learned my lesson!

Readers of long memory will recall the dual-path assist air setup that pushes 2 l/m through the nozzle when the LightBurn layer has AIR disabled, specifically to keep smoke out of the nozzle and away from the lens; that gentle breeze doesn’t push smoke into the paper.

FWIW, that’s why I run a set of test cards before I do anything fancy for the first time.

2026-02-27

Category: Science

PolyDryer Humidity: April-ish

Basement Air Filter Box: Ewww!

Prusa MK4 Foam Feet: Embiggened

Alumina Desiccant: Regeneration Timeline

LED Garage Light: Autopsy

Polydryer Humidity: February

Punched Cards: Paper Matters