Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
Category: Science
If you measure something often enough, it becomes science
A pair of PolyDryer boxes has been holding black and gray PETG-CF for a while:
PolyDryer – PETG-CF – 32 pctRH Black 31 pctRF Gray
A few days ago I slipped humidity indicator cards into the boxes:
The black PETG-CF card suggests 30 to 40 %RH:
PolyDryer – PETG-CF – 32 pctRH Black test card
Yes, I dropped that card into the box upside-down.
The gray PETG-CF card shows similar results:
PolyDryer – PETG-CF – 31 pctRF Gray test card
The desiccant in the black PETG-CF box weighed 80.9 g, a gain of 5.9 g = 10.8%. The chart suggests that corresponds to 35 to 40 %RH:
Desiccant adsorption vs humidity
The gray PETG-CF box had 102.0 g of desiccant. I apparently loaded 25 g in the meter container and 70 g in seven tea bags, but I don’t trust those numbers enough to go any further.
Unlike the black PETG box mismatch, these black PETG-CF numbers seem plausible. The results may depend on allowing far more time for the filament + air to equilibrate with the desiccant tucked in its containers than the days I’ve been giving it.
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.
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.
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.
A critter made off with our battered plastic rain gauge, so I set up an Ambient Weather WS-5000 station to tell Mary how much rain her garden was getting. I added the Official Bird Spike Ring around the rain gauge to keep birds off, but robins began perching atop the anemometer while surveying the yard and crapping on the insolation photocell.
After a few false starts, the anemometer now has its own spikes:
Weather station with additional spikes
It’s a snugly fitting TPU ring:
Weather Station Spikes – build test piece
The spikes are Chromel A themocouple wire, because a spool of the stuff didn’t scamper out of the way when I opened the Big Box o’ Specialty Wire. As you can tell from the picture, it’s very stiff (which is good for spikes) and hard to straighten (which is bad for looking cool).
The shape in the middle is a hole diameter test piece. Next time around, I’ll use thicker 14 AWG copper wire:
Weather station spikes – test piece
The test piece showed I lack good control over the TPU extrusion parameters on the Makergear M2, as holes smaller than about 2 mm vanish, even though the block’s outside dimensions are spot on. This application wasn’t too critical, so I sharpened the wire ends and stabbed them into the middle of the perimeter threads encircling the hole.
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It just barely clears the curved air guide inside:
PolyDryer airlock plate – tiny fan installed
The tea bags full of desiccant allow some wind between them and the filament in the spool, but I obviously must re-think that setup. There’s enough clearance for what should be reasonable circulation, so i defined it to be good enough for now.
The box of TPU started at 25 %RH, dropped to 22 %RH overnight, then returned to 25 %RH the next day:
PolyDryer TPU – 25 pct RH
Now that I’m watching more often, I’ve seen the meter glitch to 10% for a few seconds:
PolyDryer TPU – 10 pct RH glitch
A humidity indicator card suggests the air is under 20 %RH:
PolyDryer TPU – humidity indicator card
It may be the filament can outgas water vapor as rapidly as the desiccant can remove it, but I expected the fan to make at least a little difference.
The Basement Shop has 50±5% relative humidity, with the top held down by a hulking dehumidifier (plus a box fan stirring the air) and the bottom supported by being a basement. As a result, the 3D printer filament stabilized at about 50% RH, which seemed to work well enough for PETG.
That’s activated alumina desiccant, mostly because it’s reputed to have more capacity and a lower ultimate humidity than silica gel, but it likely doesn’t make much difference.
In addition to 25 g of desiccant in the PolyDryer meter case, I dropped five teabags holding 10 g each in the bottom of the box for more capacity. I measure the desiccant by putting 75.0 g into a cup, putting 25.0 g in the PolyDryer meter box (aided by a Polydryer Desiccant Funnel), 10.0 g into four teabags, and whatever’s left into the fifth teabag, thus eliminating rounding errors in the smaller quantities.
The stabilized humidity inside the boxes seems to depend on the amount of filament on the spool:
Nearly full → 25% to 30% RH
Half full → 20%-ish RH
Nearly empty → 10% to 15% RH
I think the humidity level comes from the filament outgassing water vapor through its (limited) surface area on the outer layer around the spool. The difference between that rate and the desiccant’s ability to remove water vapor from the (unmoving) air in the box sets the stable humidity: more surface area → more water vapor → higher humidity.
After the filament eventually dries out, the humidity should decrease, but diffusion is a slow process. More likely, the humidity will remain stable as the printer pulls filament from the outer layer and exposes the somewhat wetter plastic within.
The heater and fan inside the PolyDryer base unit circulates hot air through the box around the spool, but depends on the desiccant to remove water vapor. Running the base unit for 6 or 12 hours makes little difference in the stabilized humidity, so I think the desiccant is doing the best it can as the filament outgasses more water vapor.
Using Air Exchanger vents seems to make no difference, likely because the desiccant must then pull more water vapor out of the incoming 50% RH basement air. A psychrometric chart says 50% RH air at 60 °F becomes 10% RH air at 120 °F, but moisture in the filament wrapped around the spool can’t escape any faster.
So, for example, a full spool of TPU starting at 25% RH:
PolyDryer humidity – TPU start
Six hours of drying pulls it down to 22%:
PolyDryer humidity – TPU finish
After sitting overnight it’s back at 25%:
PolyDryer humidity – TPU after 14 hr
Admittedly, that was with the vents in place, but the closed box started at 25% RH after sitting around for a week or so following a similar drying cycle.
The desiccant had absorbed 4 g of water since I put it in, so it hasn’t been entirely idle.
Which suggests 75 g of activated alumina desiccant is workin’ hard and doin’ swell in there, with the filament acting as an essentially infinite reservoir of water vapor.
I haven’t noticed any particular difference in PETG print quality and the TPU hasn’t gotten enough mileage to notice much trouble, but reducing the MMU3 buffer clutter was totally worth the effort.
After about 7.5 years (!) the 64 GB card in my Sony HDR-AS30V helmet camera breathed its last:
SanDisk 64 GB MicroSD card – end of life
Over the course of several rides I noticed many video files ended prematurely or would not play. I gave up attempting to reformat the card in overwrite mode using the Official SD Card formatter after four hours, which says the wear leveler in the card has no spare capacity.
In round numbers, I ride 1700 miles a year at 12 mph, so the card recorded 1000 hours of 1920×1080 video at 60 frame/s, storing one 4.3 GB file every 22.75 minutes for a grand total of 12 TB of data.
A new Sandisk 128 GB High Endurance card cost a third of what the 64 GB card did and, after setting the partition label to AS30V, it’s off to a good start:
Street Lamp Pole – Rombout House Ln – 2025-05-07
That’s the street lamp pole installed on the replaced base at the corner of Rt 376 and Rombout House Lane, with the barrels gradually being pushed closer and closer to the pole by turning traffic on the newly paved lane.
That pole is not going to see the end of this year.
The Smell of Molten Projects in the Morning 