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.

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:

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.

Perfect prints produced by Prusa printer

It printeth! Verily, it printeth! My new Prusa i3 mk3s printeth! And wow, does it do a good job of it. Here's the obligatory Benchy McBenchface, in a quality I haven't even gotten close to on my old printer:

None of the sloppiness around the brow, no extra lines around edges, the print on the bottom totally clear, and it's almost possible to read the tiny writing on the aft. Impressive!

I got this as a kit (of course!), and putting it together was pretty easy, though not trivial. There's quite a tome of a manual, with each step illustrated with photos and text. No soldering is involved, and all the necessary tools were provided. On the down side, some texts were ambiguous ("put the screw in the left hole" - but I can turn this thing any which way!) and the photos were not very good, especially since they had to show details of black on black. I could certainly take better shots (and did a couple of times, just as a sample). I worked together with my friend Christina, and we only made one mistake where I had to go back and undo some of the assembly. Inserting the nuts was sometimes tricky, in most cases we were able to pull them in using a screw from the other side, but not always.

The basic design is the same as my current one, with the bed moving in the Y axis, the extruder running along the X axis, which is in turn lifted by threaded rods on the Z axis. The details have improved a lot, though. Gone are all the endstops, since the motors are able to sense when they skip, which is enough to detect the end. The extruder has a built-in filament sensor, so it can stop printing if running out of filament. There's also a power panic system in case of power outages. The bed is with a separable bendable steel plate, held on by so many magnets that there are warnings not to use it if you have a pacemaker.

The operations are also very easy. There is a panel in front with a little dial, which allows controlling the printer in many ways. Starting a print from an SD card is three clicks away, and it auto-calibrates the bed height before each print. The self-test and larger calibration was quite effective, pointed out an issue I had missed.

For Z axis calibration, there is a live adjustment option, so while the print is happening I can adjust - micrometer by micrometer - how close the the bed the first layer should be. To get the right height, I printed the Prusa logo model that came on the SD card, adjusting the height by 0.05 mm every two centimeters or so. I stopped printing after the first layer, so I could see the quality:

Top side of print. Left part is with the nozzle closer to the bed

Bottom side of print. Left side is nozzle closer to the bed. 

It was clear when the nozzle was way too low or way too high. In between, at about -0.95 to -1.1, the printing was just about perfect. This is a way better calibration than the single-strip built-in method.

The main problem since I got printing going has been to make the prints stick during printing. At first, I just used the recommended isopropyl alcohol swap to clean the plate. That didn't help much. Increasing the bed and extrusion temperature made it possible for a large flat piece to stick. Washing thoroughly with soap made things somewhat better, but printing this little hedgie proved too much for that. Next step was my trusty hair spray, which didn't help either. The trick from this video of putting a bit of gluestick on and spreading it with alcohol made no difference whatsoever. Only when I smeared the printing area with gluestick did it actually stick, but then that also adds more thickness. After reading various discussions about this problem, I ordered a flat sheet instead. It's supposedly less durable, but being able to print without smearing the plate is important.

I also ordered some filament - this is a 1.75mm extruder where my old printer is a 2.85mm - and some different-sized nozzles. I even got one of the experimental 0.15mm nozzles, since I want to try printing miniatures for gaming. I understand even using the 0.25mm one is tricky, so I don't expect instant success. I grabbed a 0.8mm nozzle for the old printer, it can be relegated to the easier tasks.

All in all, this is a really nice printer. The printing world has moved a lot since I got my Mendel90 half-kit, and it shows. I expect (hope) to be able to spend less time repairing the printer and more time designing.

The new wonder! What shall I call it?

An upgrade

The last post showed the broken foot pedal on our bio garbage can. I managed to epoxy it back on, but because it was so cold where I did it, the epoxy didn't fully set (and ran over the support so I had to cut through it), and within a month of further stepping, it broke off again. No saving it this time.

My printer has mostly been standing still, partly due to my own carelessness, partly due to parts failure. I neglected to level properly before a big print and ended up with so much backpush that the filament stripped, then the rest of the filament in the hotend oozed out. This resulted in stuckness that couldn't be resolved with a cold pull, because there just wasn't enough heating up going on. In the end I took the cooling part of the hotend off and placed it on a toaster (flatbed style, known as "Deathtrap" to non-Danes) until the filament became soft enough to pull. This bought me a bit more printing time before the aforementioned cracks reappeared, and I'm not going to try to re-glue that piece. Fortunately, I had printed another extruder block, which I'm now cleaning of excessive elephant's foot before mounting. I also tried, for extra reinforcement, to apply some contact cement to the side of the block. I imagine it can seep in through tiny cracks and bind it together a bit. Would be interesting to compare epoxy and various glues not for bonding two parts, but for reinforcing one.

In the meanwhile, I have turned 50 (who'd have thunk?), and in that connection my wife arranged a Christmas and birthday gift conspiracy to get me a new printer. Enough money came in to get me a Prusa i3 mk3s, and maybe also the MMU. It should just barely fit in my workbench. While the Mendel90 has been good, it has also suffered from some build problems and limited upgradability. The rest of the world has moved on, and getting proper bed levelling, motor feedback, a large print volume, a better plate, and many more improvements will allow me to focus more on the design part than on maintaining the printer. I will probably still keep the old one around (somewhere) for when I need more printing done quickly, but my day-to-day printing should be easier with the Prusa.