Dehumidifying methods

I've had the worst time with my PETG filament, test prints literally exploding during the print and finished prints being very brittle. The most likely explanation is that the PETG is too moist, it's supposedly very sensitive to that. My friend Christina got me some Lock & Lock boxes, they are nice and quite airtight and fit four spools very nicely. So, it's time to dry things up!

My first drying attempt was a Drybag™, which I think I put in on January 12th. It didn't make a noticeable difference. The next attempt, based on the recommendation for drying wet phones, was rice. I used a wild&long rice mix, starting 2021-01-24. It didn't do much either. Next up, baking soda, starting 2021-01-30. Nothing really noticeable.

Sure, I could try with actual commercial desiccant bags, but where's the fun in that? Also, they're somewhat expensive. So based on a suggestion from the almighty Internetz, I got some silicate cat litter. It's quite cheap, so I figured why not?

On 2021-02-09,  I just put two ramekins with cat litter in. This time, to get a more precise measurement, I also dropped in the little temperature and humidity logger I found at the local measurement instruments store (yes, we have a measurement instruments store in my neighbourhood). The humidity changed drastically - but to more humid! It ended up at ~60%. In this chart, the X marks are where the humidity sensor picked up movement. You can see it matches drops in humidity when I take out the box and open it on the evening of the 9th and on the 12th.

On 2021-02-11, since there was a nice frost going on, I figured the frosty air would be very low humidity and would allow the silicate to evaporate off some water. I left some outside overnight and put it back in in the morning, this time in a little custom box I had printed in the meanwhile. Not any better. You can see a brief dip in humidity and temperature, but it quickly goes back up.

My next attempt was to bake off the humidity. Not wanting to use devices that also get used for food, in case there are other things in the litter, I used Deathtrap, our Danish-style toaster. I poured some litter into a container made of aluminium foil and set it to toast outside, stirring a couple of times. I could sit inside and watch the steam come off, but after half an hour I could see no more steam. I stirred it again and let it cool down to merely warm, then just plopped the foil container into the filament box (which had been standing open, letting it get back to the ~30% humidity in the room). 

I did this twice, the second batch letting it have over an hour of baking, and boy did this make a difference! You can see where I take out the box and open it in the morning, and it drops from 63% to 33%. Then there's a temperature peak when I put in first batch of still-warm litter, and the humidity drops to about 15% relative (relative to the now warm air, of course), and evens out at 24%. In the late afternoon, I put in the second, longer-baked litter at 18:00, after letting it cool off for a bit. Bam! Single-digit humidity!

I left the humidity logger in there for several days after, and the results were curious. The box stands in a closet in my bedroom, and I always sleep with my door tilted open a bit, for coolness and fresh air. You'd expect the humidity to change smoothly along with the temperature when it's just left to its own devices, but that wasn't quite the case - or at least the measurements didn't follow that pattern. See how in the first day, when the temperature starts to drop, the humidity almost doubles over 45 minutes, then stays at almost exactly 10% for most of the night, only to drop off much faster than the temperature rises come morning. And then this effects slowly disappears over the following days. I would love to hear an explanation for this!

I can also confirm that the Prusa doesn't like when it's this cold. When I tried to start a print one of these cold mornings, it refused, claiming there was an error in the thermistor! Being metal, the bed had gotten even colder, and the temperature readings started at 11ºC, even though the room was warmer.  Here's what it looked like a bit later, I was able to print shortly after this.

Tests of magic numbers, part 1

 There's some talk about "magic numbers" in 3D printing, the idea being that the Z stepper motors are more precise when aligned with full steps (or somewhat with half steps). Others say that it doesn't matter with modern precise printers[1], and that since the stepper motor starts at some random state, using magic numbers won't help. With my Prusa i3 mk3s, I certainly have a modern and precise printer, so let's find out!

First, the magic number. Prusa i3 mk3s steps/revolution at a step angle of 1.8 is 200. By marking the Z threaded rod and moving the Z axis, I found that one revolution is 8mm. 8mm/200 means the magic number is 0.04mm - confirmed by this thread. One should thus always use layer heights that are a multiple of 0.02mm (because a half magic number is still OK, with the motor evenly balanced between two magnets).

Now to deal with the random initial state. The initial state could be reset by briefly disabling the stepper motors. That would offset the Z level by at most 0.01mm, less than I adjust the Z level by, and thus not a concern for bed levelling. So if I try with and without magic number layer height and with and without aligning, I should be able to determine if it really makes a difference.

This is the required GCode in the 'Before layer change G-code' section:

; Briefly disable Z motors before start to align magnets. 

{if layer_num == 0}

M18 Z

G4 P10

M17 Z

{endif}

First I tried with just plain DasFilament PLA and my current nozzle, because that's what was in there.

Here's a shaman with 0.2mm layers and alignment, two detailed areas zoomed in:

Details in larger:

The same shaman with 0.19mm layers and no alignment:

Details in larger:

There are some differences to be seen, but you have to look carefully. My current nozzle has been used for a while, including with UniCoFil filament and sparkly filament. Maybe it's a bit worn. and maybe the DasFilament filament doesn't match the settings as perfectly as Prusament does. 

So next I'll switch to a fresh 0.4mm nozzle and freshly unpacked Prusament and do a test piece with 0.2mm and 0.1975mm - one microstep away from a full step, presumably the worst case. Then I'll try with 0.1175mm unaligned and 0.12 aligned, probably the finest a 0.4mm nozzle can realistically do. Then I'll switch to my slightly used 0.25mm nozzle and go extreme: 0.04mm (yes, that's 40 microns) and 0.0425mm layers.

[1] Some of the posts in that thread get the numbers quite wrong, which is why I went to manually confirm the mm/revolution.

A UniCoFil vase

Back in August, I did some more prints with the UniCoFil filament after replacing the heatbreak. It's possible that replacement wasn't necessary, but I will never know. Even after that, the stripping continued, though possibly not as often or as much. After printing out a failed hexagon vase that simply came apart at a layer that had stripped, I changed the filament settings to a) have a 1.0 extrusion multiplier, and b) extrude at 230°C. That eliminated the stripping, and I was able to print this nice small vase:

Just goes to show that each filament has its own best settings. 

Stripped again, and out of tubes

I was trying out some semi-transparent blue filament from UniCoFil. The temperature tower had quite a bit of stringing, so I tried with 2mm retraction. That, unfortunately, led to stripping when the next temperature tower got to 195C. Despite trying to help the filament come out, unloading didn't work, so I had to snip the filament and open up the extruder.

TIP: When snipping the filament, do so with as much filament above the PTFE tube as possible, to more easily grab it later.

I disassembled enough to have the heater assembly free and tried a cold pull, but there wasn't enough filament sticking out to get a good grip. So I unscrewed the heatsink (this time the heatbreak didn't follow) and could get the PTFE tube out easily. Not so the filament. I tried heating the tube on the bed and then pulling, but again with not enough to pull on. Eventually I used a small hex wrench to push out out from the other end, which worked.

Then I put the PTFE tube back in the heatsink, which was a mistake. I put it so far in that I couldn't screw the heatsink onto the heatbreak, and I wasn't able to pull it out without destroying it. Fortunately, I had a second one. Need to get more replacements, and maybe just a spare of each part.

Having mounted the heatsink on the heatbreak, I could insert the PTFE tube, but not quite enough, now the end would block the gears. So I took it apart again, pushed the PTFE a bit further in, and then it looked OK from my point of view. Not so from an actual functional point of view, it was high enough to hit the gears still. It needs to be barely visible above the edge of the hole.

I tried to align it better, but it took more squeezing than it really ought to, and one I had it in, the nozzle ended up being too low, possible because I couldn't screw the heatbreak far enough in. I will order a bunch of new tubes and spare other things, take the whole shebang apart, and then try first to install from fresh with a new tube, if that doesn't work then replace the heatsink - I think the black insert inside it has gotten damaged.

Hey, Slab!

Today, I decided it was time to reduce the noise of my printer.

First I did some measurements. I created a single-layer print of pure infill, increased first layer speed, and adjusted infill angle to make the printer move X, Y, or diagonally. Sure, I could have done a custom gcode sequence to just move the axis, but I didn't feel like digging into that. The first print was quite difficult to get off, so I moved Z adjustment from -0.8 to -0.6.

For each test, I used the Sound Meter app, first right in front of the printer, then on a separate table across from the printer, taking the average after about half a print. 

Y movement: Near printer 56 dB, other table 46 dB

X movement: Near printer 54.3db, other table 37.2 dB

Diag movement: Near printer 57 dB, other table 45 dB

Y movement is far noisier than X movement. There's some suggestions in this thread: Lubricate bearings, oil axis, add motor dampers. Oiling is an easy step, let's try that. After oiling, Y axis movement is 56.7 dB near the printer, 46.7 dB on the other table. Louder. Huh. Could be a measurement error.

I don't feel like taking the printer apart today, but I did get a slab of granite, and I have plenty of foam. So let's do some tests with them.

First step: Put pieces of simple camping foam under the feet of the printer. This reduced the noise level of the Y movement to 48.3 dB near the printer, 35 dB on the other table. Already noticeable! And this foam is pretty stable, so shouldn't make the printer too wobbly.

There's also a sound coming from the power supply, probably the fan there. Slightly irregular, not that loud yet.

I took the opportunity to fasten what bolts I could get to. I tried to open the power supply, but wasn't able to without taking more apart than I felt like. I did however notice a small piece underneath it that wasn't fastened correctly, so I fixed that. After that and putting the printer on a slab with soft foam underneath, the test print measures 40.4 dB near the printer, 31.5 dB on the other table. So this shaved off in total 15 dB, impressive! Even the power supply fan seems quieter.

Of course, I should have measured between fastening bolts and putting it on a slab, but I didn't. Maybe another day.

Luckily, the filament spool just fits under the cabinet above

I might want to have the filament spool mounted separately, possible between the two edges on the sides (you can see one in the picture). I would need a setup where the holder was easy to remove, though. I suspect some of the noise from fast moves is from the filament spool.

Clearly, this merits printing a really nice McBenchy!

There's a smidgeon stringing (that I have cleaned off), and the Z level is not quite perfect, but overall it's super smooth.

The first layer of the McBenchy had an average noise level of 34.9 dB (measured in front of the printer), the second one where the usually noisy bed fan started got up to 39.5 dB - that's not just the fan, though there were also some fast zig-zag moves that were somewhat noisy. Apparently moving the printer about has at least temporarily fixed what was wrong with the fan. Later layers averaged 37.7 dB, though there were places that were somewhat louder, it seems to occasionally hit a resonant frequency. Measured on my chair arm, so at normal distance for me, it's 29 dB, at the other table 28.2 dB.

All in all, I am satisfied with this noise improvement. In fact the power supply is not responsible for a fair amount of the noise, maybe I could dampen that by adding some rubber washers to the various screws.

Obligatory Borderlands 2 reference:

Last miniature test, I promise

Having had some luck with the 0.04mm layer (yes, that's 40 microns, less than what many resin printers advertise), but also having read that thinner layers may need higher temperatures, I tried to vary that. Also, due to stringing, I tried to vary retraction. Results were mixed, shown  belowwithout any cleanup.

This one (front and back) is (accidentally) at 230°, with 1.2mm retraction.

This is also at 230°, with 2mm retraction:

And finally, at 235° and 3mm retraction, an accidental skeleton king:

Clearly, 235° is too much, though it should also be mentioned that these were done after a failed attempt at a temperature tower that broke loose from the print bed. 230° is also a bit high, I liked the 225° better, the print was smoother. And 3mm retraction is quite obviously a bad idea here. 

This temperature tower was done at 0.16mm layer height, still 0.25mm nozzle, and it's really hard to tell any difference between the temperatures. Actual temperatures are, from the bottom, 225, 215, 205, and 195. There is a bit more bridging droop at 225, and the overhang seems a bit less regular at 205 and 195. The most interesting difference is that at 195, the surface is matte rather than shiny. 

Full-size front shot, layers clearly visible:

These shots were taken in my new mini-softbox, a cut-open plastic container. It can bounce the light enough to give reasonable shadow,s while the highlights of irregularities are easy to see in the sun. Lens is a 60mm macro at 1:1, f/16 on APS-C.

Now back to a regular 0.4mm nozzle and some normal prints.

Prints That Go Boom in the Afternoon

More work on the temperature tower, since I want to calibrate that for PLA as well. Also, I should probably calibrate it separately for separate nozzles sizes. Anyway, feeling too lazy to change all the numbers in Bob long if-clause, I change it to this:

; For Fast_Informative_Temperature_Tower, 10 levels at 8mm

M104 S{230 - (4 * int((layer_z / 8)))}

While this doesn't show the exact temperatures at each level, it is a lot more concise and easy to adapt to other temperature combinations.

Printing the temperature tower with the 0.25mm nozzle takes a lot longer than with the 0.8mm, but it actually looks nice, and doesn't wobble eerily when printing the top. This minimal tower is rather unstable.

The PLA tower with 0.25mm nozzle is simply... perfect. At all temperatures from 230 to 190, no stringing, no change in the quality. I had to go into the gcode and double-check the output from above to convince myself that it was doing the right thing. 

No, it's not twisted, that's just the perspective.

A PETG tower with the 0.25mm nozzle (Z offset -1.05) and temperatures from 250 down to 210 gave me an entirely new experience: An exploding print. I was sitting next to the printer when I head this sound of plastic bouncing around, and this is what I saw:

Look in the background, there's where the parts landed.

The pieces collected. A part of the foremost pieces has also fractured off, but stayed put.

At too low a temperature, the print simply fractured - probably from the stress of being pulled back and forth. It's really difficult to see the stringing, but I think 230 is about the right temperature. Unless I am missing a chunk, it broke off while printing the 224°C layer. So my previous test with the 0.8mm nozzle giving the best result at 220°C doesn't work well here.

I'm surprised that this would happen with PETG, it's supposed to be less brittle that PLA.

Temperature Towers and other tweaks

As mentioned in the last post, I did some temperature towers (using Bob's sneaky gcode) and found better settings for PETG. The standard towers are a little too detailed to work well with the 0.8mm nozzle, but I tried anyway. Here are the Fast Informative Temperature Tower, at 4 different retraction rate settings (default 1.4, 2.0, 2.5, and 3.0):

String galore, but less so at about 220°C and 3mm retraction. I don't think I want to retract more than that, I see several sources saying it can lead to hot plastic getting too far up towards the PTFE tube.

My 0.4mm nozzle was pretty full of PLA. I didn't want to scratch it using any kind of metal tool, instead I heated it up in a candle flame to get the PLA soft enough to run out. I would have preferred a butane lighter, but ours was out of fuel. The PLA didn't run out on its own, but I was able to attach a piece of filament and 

For PETG, I'm using the steel powder bed, as the smooth one just doesn't let go of the print, and for the 0.8mm nozzle with 0.4mm layer height, I have calibrated it to a Z level of 1.150. The layer height does make a difference for that. 

I'm using the stealth mode more. It is really a lot quieter (average 46dB instead of 52, measured with a phone app, the phone lying right in front of the printer) and only minimally slower, but it turns off crash detection, which I definitely want to have on when starting a print and leaving. When I'm watching the print, it's not so bad.

Printing at large

With the new powerful 0.8mm nozzle in place, it's time to print more things!

First thing: Feet for our shoe bench. Its current height is such that the Roomba can almost but not quite get in there, and might well just get stuck. So I designed some simple feet, rounded and flanging out towards the bottom. My goal was to make it slope non-linearly, but I started with the straight slope and did a test with that. Doing a draft print using minimal infill and thin walls, I was still able to not just sit on the corner it was supporting, I could plop myself down with force, and all it would do was creak.

Having confirmed the design, I added a simple function to curve it. The trick to that is to create a function that goes from 0 to 1 but with a slant. Good candidates for this are square and square root, this is what I ended up using:

/** A function that given i from 0 to max starts at 0 and ends at max,

    but slopes inwards in between. */

function inSlope(i, max) = i * (sqrt(max/i));

Note that I give it not a value between 0 and 1, but two values that combine to give that. That makes it easier to plot into an existing design. This gives a pleasant volcano-like shape:

With the 0.8mm nozzle, I can print two of them in 1h18m, using 68g of filament. With a 0.4mm nozzle and the default 0.2mm Speed setting, it would take 3h3m but only use 53g - the difference in filament use probably due to the infill being twice as thick without there being half as much of it.

While printing the second pair, the printer did something amazing that I never expected to see. Part of the edge of the first layer had curled up on itself (probably should tune the Z offset separately for each layer thickness), so when the hotend came back to that spot on the second layer, it hit this bump. At which point, it said "Crash detected", moved the hotend off to one side presumably to wipe it clean, then moved it back and simply continued printing! More simplistic printers would either have torn off the print, leading to a messy blob on the hotend, or at least have pushed the X axis out of whack. I had at most expected it to detect the crash and stop, not to fix it itself!

Here's the final result in action:

Next thing is a hook for our fly zapper, which has otherwise had diverse less-than-optimal homes and which also has a rather strange loop for hanging it, so normal S-hooks tended to fall off when removing it. We happened to have some shelf railing pre-installed in a tiny side room to our kitchen, so hacking up some hooks for that was simple. The prints did end up being larger than would fit, so I had to redo it a few times. I guess the 0.8mm nozzle is too imprecise for this kind of work, but with a few adjustments it worked:

I was also looking at doing some auto-watering boxes, but the size I wanted turned out to make it use more filament than I found reasonable.

For the dresser next to Mickey's comfy chair, I made some simple hooks fitting the top edge, allowing her to hang some bags there:

Weird-eye view of the hooks

And finally, in preparation for getting more filament (the white already ran out), I printed two master spools, so I don't have to contribute to plastic waste with the empty spools. It's enough that I contribute with failed prints. The astute observer will notice a veritable spider's net worth of stringing here. Those can be melted away relatively easily with a flame, but it would be better without them. I did some temperature towers (using Bob's sneaky gcode) and found that a combination of printing at 220°C and 3mm retraction gave much better results.

With default settings

With 3mm retraction, 220°C

Bigger is better!

Last episode: I broke it :(

This episode: I fixed it! :)

Turns out the heat assembly works much better when you assemble it according to the instructions rather than just in whichever order. In particular, the nozzle should go in first, then the heatbreak, not the other way around.

Because I've been wanting to try it out, I replaced the old nozzle (which needs cleaning) with a 0.8mm one. That, of course, is an entirely different beast, whose main purpose in life is to squirt out as much hot PLA as it possibly can. Without breaking things, that is. Having little idea how much that actually is, I searched and found this wonderful site crammed with useful information: http://projects.ttlexceeded.com/ (a.k.a Muppet Labs). Several pages there are dedicated to how to work with different nozzles (which he likens to using different lenses on a DSLR, in particular that it's an important feature and if you're not using it, you're not getting the best out of your printer).

The first thing is calibrating volumetric rate. The Maximum Volumetric Speed is MVS = Extrusion Width X Layer Height X Speed, and is supposedly 15mm^3/s. I'm going to follow Bob's instructions on how to calibrate, which requires manual control. I've connected the printer directly with USB using Pronterface. Ah, a familiar face. In some cases you just need full manual control. Pronterface lists the extrusion motor speed in mm/min, the default being 100mm/min. The cross section of 1.75mm filament is 2.405mm.  Then 100mm/min = 2.405 * 100 / 60 mm^3/s =  4 mm^3/s, noticeably lower than the possible amount.

Bob says to use 60mm of filament per test. I'll start on that once I get up near the limits, at first I'm just checking that things work (including that there's no filament oozing out around the heater block). Finalizing the nozzle insertion, I first run a PID Autotune (M303) which has the printer figure out how the heating behaves - a nifty trick I hadn't heard of before. Since I usually run my filament at 215°, I should tune it there. I happened to first just do the default 5 cycles at 150°, then following this page on reprap.org did 8 cycles at 200°, then used the built-in autotune from the menu. The original values, as told by M503, were Kp: 16.13 Ki: 1.16 Kd: 56.23. At 150°, the final values were Kp: 21.45 Ki: 2.20 Kd: 52.33. At 200C, they were Kp: 20.45 Ki: 2.07 Kd: 50.46. So there was definitely a difference from the original.

It's unclear if the time needed to heat up from ambient temperature figures into the PID values, so I let it cool down to 39° before the 215° run, though I don't remember if I did so before the 200° run. The 215C run gave Kp: 20.85 Ki: 2.06 Kd: 52.64. I ran one the next morning from totally cold, which gave Kp:20.46 Ki:2.00 Kd:52.25 It automatically stores it when run this way, so that's easier (as expected). And given how little variation there was between the last runs, I'll just take what the built-in autotune set.

Next step is heating to 285° and giving the nozzle a final slight tightening. I wish I had an electric screwdriver with torque limit showing actual Newton values.

Now for the extrusion speed test! With heat at 215°, starting at 100mm/min, increasing by 100 at each try, I got clicking at 500mm/min, but was able to extrude at 490 without clicking, an impressive 19.6 mm^3/s. However, from 250mm/min and up, it would increasingly curl up on itself after an initial straight line, a sign that it's not able to heat it to full temperature. Trying again at 200°, I accidentally ran it at 3000mm/min, which unsurprisingly it wasn't too happy about. Instant stripping. Whoops. Fortunately, the filament wasn't broken, so I could help it unload and then reload.

Running at 300mm/min shows some curling of filament, at 400mm/min it curled enough to twist back on itself and hit the hotend. I suspect that while extruding, it doesn't apply nearly as much power as when heating, because it just tries to keep the temperature steady, but doesn't take the amount of filament fed through into account. I can see it being difficult to adjust correctly, but also leading to much faster printing if done right. There's probably other problems I haven't considered, lots of smart people have thought a lot about this.

In any case, I was able to start printing again, and at about twice the speed of the 0.4mm nozzle.

Nothing good lasts forever

Hot (or rather, not so hot) on the heels of boasting of my many successful prints comes a tale of woe and sorrow! Woe! Sorrow! Or at least some technical problems.

While printing a faucet filter tool of presumably the right size for ours faucets (I was too lazy to measure), my white filament ran out. Supposedly, the printer should handle this nicely, running an unload procedure immediately. For whatever reason, it didn't, just letting the filament continue through until it was past the drive and thus the point of no return. Apparently, but I didn't know at the time, it's feasible to just feed in more filament immediately, but I tried re-running unload, then pushing the filament piece further down. To no avail, it was stuck.

Opening the side (which hinges up nicely), I found a lot of white debris (it had ground down the end of the filament). After vacuuming most of it up, this was the sight that greeted me:

Taking a closer look with my proper camera, it was clear that the filament sat in a PTFE tube and wasn't a giant blob or anything.

So I tried pushing some more, at higher temperatures, but it wasn't budging. Eventually, I had to take the hotend assembly out, and since I'd probably need to take out the nozzle anyway (one page suggested removing the nozzle and then heating), I would swap to my 0.8mm MegaNozzle shown below (banana for scale):

After getting a set of inverted hex bits (very useful!), it was easy enough to unscrew the nozzle, but that didn't help with the blockage. Fortunately for me, they had designed the whole thing so that taking out the hotend is relatively easy, and I was able to unscrew the heatsink and heatblock. They advice against unscrewing the heatblock, but I didn't see how to avoid it, since it's not really accessible. Anyway, with that out, I was able to heat it in the oven and carefully puuuull out the filament until it went "plop" and popped out. This was essentially the classic cold pull, though possibly a bit too cold due to not having the right tools right at hand at first. The PTFE tube needed replacement, but fortunately my kit came with two spares - how prescient!

So I reassemble the whole thing and run a test without filament - after all, I need a nozzle in there first, which requires 285C. Alas, the heating is bad - it heats up, but very slowly, at 100C about 1C per second. I didn't let it run for long enough to get up to full temperature, it took over a minute to get to 135C. To check that it wasn't the thermistor misreading it, I poked an old PLA print at the heat block, but it only deformed slightly, so it definitely wasn't doing runaway heating. That's something at least, overheating could be quite dangerous. But I'm still stuck with bad heating. I double-checked the wiring in the board, and the resistances and voltage were correct. So either there's a loose wiring in the heatblock end, or... something else.

Many good prints done

Using PETG from Beta2Shape on the steel dust surface, I calibrated it to -1.09mm. Prints still fell off unless I used 3dlac. When I tried the flat surface, I was hardly able to get the print off at all. There is also a lot of very fine stringing when I use the default Prusament PETG settings. I'll try some of the tips in https://all3dp.com/2/petg-stringing-3-easy-ways-to-prevent-it/ to improve that.

For PLA, I couldn't use the steel dust surface, instead I use the flat one calibrated to -1.0mm. The PLA from DasFilament has done good by me. Curiously, after switching to the powdered surface and back, the calibration changed to -0.8mm. Clearly recalibration is a good idea after switching surface.

The printer has been quite busy. I joined makervsvirus.org and printed 50+ face shield holders:

I look super derpy in this shot, but it shows how the face mask works, just add a sheet of clear plastic.

50 of them delivered to our local hub.

I printed tools for my coworker Ilham for taking off the faucet filter (in German a "Percolatorschlüssel"):

Generic version that works on many faucets 

Version for a specific size of inner teeth - I didn't even know there were inner teeth! This was the size that Ilham needed, but difficult to get a good grip on

A version with better grip, but too large for our faucets. 

Some other things against Coronavirus:

My wife is doing a bunch of masks, but ran out of bias tape - as did all the suppliers. So I printed this nifty bias tape folding device, it works quite well.

Another thing for masks, this holds the straps instead of your eats getting pulled at. Unfortunately it slides downwards, and so does the mask.

And another couple of useful things around the house:

I got a used bike trailer of a kind I've previously used for the Monachium war chariot, but this one came with an attachment that tried to fill the same space as my disk brakes. Since physics has some stern words to say about doing that, I made an adapter for the other kind of attachment, printed in PETG (which is less brittle and more heat-resistant) and somewhat over-dimensioned. It works nicely so far.

For working from home, I found my WiFi connection utterly inadequate, so I decided to lay Ethernet into my room. These are Cat6-compatible clips that can be stuck onto the wall. I now have a pretty well routed wire, firmly attached. 

The new PrusaSlicer 2.2.0 has some nice details to it, like when an SD card is detected, it will add a button to write to the SD card and after that another button to eject. Now that's a UI that helps smooth the common path. Too many engineers in particular forget to do that, presumably thinking that it's enough that the functionality is available, there's no need to duplicate it. Kinda like the mathematician reducing a fire to "a known problem."