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.

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. 

Replace *all* the things!

As mention last time, I had been trying out the UniCoFil filament, first the light blue, then the fast-changing rainbow. All through that, I had trouble with stripping mid-print. I got quite good at cleaning up after a stripping incident, disassembled the heater assembly several times, even swapped out the heatsink as I had been a bit forceful on the inserts. No luck. I was starting to blame the filament, but saw that it was considered a benchmark of quality by some filament testers, so unlikely to be the problem. I also tried pushing some filament through the heatsink and heatbreak after removing the nozzle, found some scrapiness at the heatbreak area, but that's probably just because it's metal rather than PTFE. 

Taking a second look at the removed nozzle, I realized it was badly damaged on the threads. Maybe I had put it in wrong? That would certainly explain the problems. Fortunately, I had bought an entire set of spare parts for the heater assembly, so I was able to swap the nozzle and heater block. That's a lot easier with the e3dv6 than the previous systems, no fiddly wires, just two stiff metal inserts and screws to fasten them. It has now printed for several outs without any issues (jinx!).

Here's a close-up of the nozzle:

Things I learned:

• The spring-wound screw that holds the idler door in should be flush with the left side of the block when filament is in. That is the position of least stripping risk.
• The neat little cover mount I had printed for cleaning the filament made it easier for the filament to break when doing the hot part of a cold pull. It should be unscrewed and moved above where you grab the filament (grab the filament with pliers).
• The screw fastening the heater cartridge needs more force than I can apply with a normal hex wrench, I had to get a proper bit driver.
• Pushing filament out while cooling down for a cold pull ensures that the nozzle is full and so is more likely to bring debris with it out.
• The PTFE tube should be 11 mm over the top of the heatsink when in. It will be just visible in the gear chamber.

In related news, I tried using the "little master spool" designed by DasFilament, but the forces of the filament inwards opens up the locking mechanism, and I got this disaster:

Not what I hoped for. Also, it's even easier with this design to have the filament hop out sideways or get stuck between filament and spool. Need to find or make a better design. There are some promising things on Thingiverse, but right now they have a problem where occasionally - even after the page is fully loaded - the page will blank and go "Something went wrong". Web developers, have you heard of a little thing called "graceful degradation"? You should try it some day, it's delicious.

Printing with flexible filament is fun

I'm just about out of the purple Innofill plastic. For purposes of printing things for our kitchen, I'm looking for a matching red color. Turns out there's a color scale I hadn't heard of until recently, namely RAL, and some things I spraypainted were RAL 3003, a nice deep red. So let's see if that's available in filament!

At https://www.plastic2print.com/ral-classic-custom-colored-filament.html they offer any color filament you can pick out of RAL, but you have to buy 10 kg at a time, which is a bit much. They don't state the RAL for their regular spools.

At https://www.dasfilament.de/filament-spulen/2-85-mm/134/pla-filament-2-85mm-kirschrot I find exactly the right color, at an almost suspiciously low price, 16€ for 800g. Looks like they're quite active on the reprap.org forum, and I don't see any complaints there.

http://3dk.berlin/en/content/12-farben (argh! When did "berlin" become a top-level domain?) has a nice overview of their colors, but alas no 3003.

dasfilament.de it is. Got here just before we left for the US, but not in time to do anything with it. Also got a sample of PETG, which I hadn't heard of before, but sounds like it's worth trying.

I'll need to do a better filament setup. From what I'm reading, the way I've just had the spool hang loose with no guiding and letting go of the end, I've set myself up for the tangles I now suffer from. I broke the spool holder that came with the kit, plus it was for larger spools AFAICT, so now I'll just use the rest of this spool to print the holder for the next.

For a quick test print, I reduced infill from 20 to 5%, set 1 top and 2 bottom solid layers, set infill_only_when_needed to true. Then I printed a reduced version of this filament holder to check that it matches my spools. Looks good, though it was probably designed to just let the spool sit loose and accept the bit of friction. I started designing a spool holder rolling on four ball bearings, so there's practically no friction, but then it struck me that a bit of friction may be a good thing. Instead I might just want to guide the filament better, maybe with a bit of PTFE tubing and a longer way from the spool to the extruder. Only problem with that is that cold pulls become harder.

And because I was running low on the normal filament, I decided it was time to try out the flexible filament. At the same settings as my regular PLA, it came out quite nice:

This is not an extremely flexible filament, just enough that I can compress the sides of this cube. I was going to print at 25% speed, but it didn't get picked up, and printing at 100% worked just nicely. Let's move on to testing ObPhoneCase by intersection the design with some cubes and printing that.

I realize now that placing the design centered in 0,0 would have made some things easier, for instance scaling.

Looks like I set the Z adjustment a teeny bit high, but the flexible filament doesn't seem to curl when cooling, so all that does is make the bottom layer less flat. That simplifies things!

The trickiest part of the phone case is getting the holes right. While some overhang is doable, it's not so predictable. However, printing with support doesn't work so well for this kind of structure, the support generated by Slic3r is fairly heavy-handed and doesn't come off nicely in this case:



Overall the case looks good, though:



Eventually I just decided to do my own support for the holes, with little cubes literally hanging in mid-air, but with a fraction of a millimeter distance. That actually came out really nice:

They come off at a light touch (actually some fell out just due to the bending when getting the print off the bed) and leave only the smallest of marks.

New Year's break: looking at thrinter.com for information and inspiration

As I am AFP (away from printer) for a few days, no new prints for a bit. But I want to point out a web site I just ran across.

Walter at thrinter.com has a lovely overview of many types and makes of filament, including his own (extensive) experience with many of them. It's a valuable resource for anyone curious about which filament to get for their printer.

It's also an interesting source of inspiration for what and how to design, and a good place to look if you're not sure what a 3D printer is good for. In the PLA and ABS sections in particular, he shows plenty of example prints, from the artistic to the immensely practical, often with design tricks I hadn't considered and that you rarely see in commercial products. Well worth a look.

The key to success: Tighten your gear shafts!

Got a suggestion to print from an SD card instead of over the USB link, so I acquired a plain 32GB card, and after poking a bit at Linux got it to work. Except that the Marlin doesn't recognize it at all (and the USB connection resets whenever I insert the card).

Looking a bit more at what the two jumpers do. JP14 atop the board appears to be the Autoreset, necessary when uploading firmware, but might interfere with the SD card reader due to a shared reset pin. Taking it off doesn't change the reset behaviour, though, so I'll leave it on.

JP15 switches between power from USB and power from the PSU. According to this, having it away from the connector blocks means USB power, and I have it towards the connector blocks, so that should be OK. But just because I'm paranoid, I'll try a print with the opposite JP15 setting.

Once again, the extruder gets set to 200C and the bed does not get set. Also, the X axis got stuck moving towards home. That is with an admittedly slack belt. Tightened somewhat and restarted.

An annoying thing about Slic3r taking over the heating and homing is that it does the heating pause by inserting a long pause. During that time, the print cannot be aborted.

X axis problems got worse, now it can't home at all. Time to check if the motor rod is properly attached. Inspecting a stuck Home command with a flashlight shows that the rod does turn while the gear doesn't. That's one mystery solved. Unfortunately, I have no small enough hex wrench in the house. Fortunately, a tiny Philips works in a pinch.

I expect the motor would be more stable if the rod has a flat side, but alas it doesn't. I suppose I could grind it down with my Dremel (leaving tiny pieces of metal all over the place:) For now, I will just retighting and see what happens.

Again the heated bed takes quite a while and/or several attempts at setting it before it started heating, and the extruder temperature got set to 200 despite the Slic3r settings. The result looks unsurprisingly somewhat soft in the corners, presumably because there's time for a little bit extra filament to ooze out:

Tried running Slic3r on the command line, inspecting the resulting gcode. Even there, it ignores the settings, but running the Slic3r UI takes it into account. Noticed that the --load command allows multiple files to be specified, adding the ~/.Slic3r/filament/Simple Mode.ini file got the temperature right. So apparently the presets section doesn't load the right thing. But there's also a simple.ini that gets generate along with the slic3r.ini, which contains all the right settings. Pointing at that instead.

Found a hex bit set that was a gift from Ric a year ago, which contains tiny hex bits. Tightened X and Y considerably. Thanks, Ric! I still think a flat-side shaft would be better.

Took a couple of tries before I got this right - turns out it now heats the bed first, then homes and heats the extruder. Except sometimes the bed seems to get confused and either not heat or keep heating. Also, using simple.ini is not a good idea, but pointing at the three Simple Mode.ini files works (as long as you quote the arguments with spaces instead of backslash-escaping them). The entire command line is

/home/lars/Slic3r/bin/slic3r $s --load "/home/lars/.Slic3r/filament/Simple Mode.ini" --load "/home/lars/.Slic3r/printer/Simple Mode.ini" --load "/home/lars/.Slic3r/print/Simple Mode.ini" --output "$o"

Ok, so now it heats up the bed first, then the extruder, then waits for a minute before printing. Also, it's harder to trick into not printing in the middle. Ah, well. The skew is utterly gone now, to be replaced with a stringiness that I at first guess would say temperature or extrusion amount problems.

The temperature is easy to test, and I got decent results with 200 before, so let's go there.

Stringiness persists. Odd. Looks like too little filament. Tried extrusion multiplier of 1.1:

This was abandoned partway through as no filament was coming out. I marked the filament and made it extrude a set amount, but nothing came out.  Then I turned off the motors and pulled out the filament. It was stripped along one side:

Reinserting it and running again gave pretty nice results:

It looks a little blobby in the corners, and the top layers hang down a bit. I'll try at 190. After that I can attempt increasing the acceleration. This time, since it's been a bit hard to get off the print, I'm adding a raft, just to see how that works.

Raft was hard to get off. Not trying that again until I see a real need for it.

Upping the acceleration to 1/2 of the original:

#define DEFAULT_MAX_ACCELERATION      {1000,1000,150,2500}

#define DEFAULT_ACCELERATION          1000
#define DEFAULT_RETRACT_ACCELERATION  1000

This definitely helped on the corners, I'll try putting it all the way back up. The lid of the cube still sags a bit, and there are gaps between the lines. 

I wish I could add more skirts, it only barely gets to start extruding, and if any drooling happens while it waits for a minute in the corner, that's likely to get stuck in the main print, as can be seen in the bottom-left corner above.

Trying with a 1.1 extrusion multiplier.

Apparently the thing I can add is a "brim", but that actually connects to the object, not what I want. Also in this print tried lowering the temperature to 180 (185 for first layer) to see what effect that has on the corners and top sagging. It still has one corner with issues, and there's a bit of ridginess to one side:

Reducing extrusion multiplier again. And because it's getting late and this will probably be the last print of the day, I'm doing an actual useful thing: A wire clamp for the back of some LED tubes, with a nut-and-bolt arrangement for affixing a back plate. It's a continuation of the earlier design by Thomas Riedl. Also looks slightly like a space ship:

And finally, a progression of the prints that have brought me here over the last few days:

A Dance of Filaments

Next step is getting the extruder tuned. I grabbed a piece of filament from the scrap box, and went "What is this, actually?" Some googling found several methods of testing, most of which weren't practical: Burning a bit and sniffing it - no open fire in FabLab. Dunk in acetone - don't have any. Test in the extruder - not good when the extruder isn't tested yet. Break it quickly - it whitens a bit and breaks, but I wouldn't call it "snapping". Rubbing it against clothing and smelling it - no noticable smell (hints at PLA). Heating with a properly controlled soldering iron - seems to not melt a lot @200. Dipping in warm water does make it bend easily, that strongly indicates PLA.

From the last test I'm going with it being PLA. And indeed, some properly marked rolls of PLA behave the same way.

With the glass plate one, Z level is 1.6 and it's perfectly flat. Turns out I'd missed the bit about clipping on the glass plate. I have the clips, and they just barely fit in the opening, if I place them just right. Adjusting the firmware to have a Z home of 201,7. Then re-measured and subtracted another 0,2 mm to allow for expansion, and set the Z screw pointers.

Annoying thing about the clips is that one is right where the extruder comes down if I just home and then down.

Strange hiccup while heating up the extruder, the temp reading stayed the same for a while then jumped. That's potentially dangerous, but it did end up at the right temperature.

Alas, actual extrusion failed. A small amount of the previous black filament drippled out, but I was unable to force the new orange on in by hand, and the extruder motor refused to turn in either direction more than a brief second at the start.

Took out the hobbed bolt to see if it was ok, looks fine to me. Loosened the idler on the side, fastened it, no difference.

Took out the idler and looked inside. Aha! A stump of old filament from mid-bolt down. Heating up the hot-end, I was able to pull this out. Didn't help on getting more in.

On a lark, I looked at what happeend when the idler was in but the hobbed bolt was out. Turns out my filament wasn't even making it through to the hobbed bolt. When in doubt, more violence! Pressing harder moved the idler aside. Knowing now how much to press I was able to do this with the hobbed bolt in, and have it grab. I then hand-cranked until I started feeling resistance, then turned on the heater and handcranked out black goo till it turned white.

Still no luck running the extruder motor, though. Tried measuring the inputs, but that's not so easy with a stepper motor's varying input. Looked like the right-hand input was at least different than the others when measuring alternating current across them, so maybe there's something up with that one.

Enough for tonight, alas. Tomorrow a more physical battle awaits (if anybody but me are crazy enough to go fight in this heat:)