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.

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.