Ed Nisley's Blog: Shop notes, electronics, firmware, machinery, 3D printing, laser cuttery, and curiosities. Contents: 100% human thinking, 0% AI slop.
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.
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.
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.
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.
The Smell of Molten Projects in the Morning 