Saturday, 4 March 2017

Moving to extruder #2

Just printing some prints:

GlassMarker - a small piece designed to sit on the rim of a water glass, so we can tell which glass is whose. I'm trying for a fit that makes it not move along the rim.

And now the white filament stripped. Curiously it can still extrude in reverse, but stops when it extrudes forward to a certain spot. But as promised earlier, this means it's time to switch to the mount I paid for.

Getting the support out was relatively easy, certainly more so than with my own print. A bit of digging around the edges, then push, and it went pop. The flat nut trap was a perfect fit. However, the deep nut traps were a different issue - they were just slightly too small on the sides, on the order of 1/10th of a millimeter. This is well within the promised spec, but a problem here. Dremeling it out didn't work well, so I went and got a set of tiny files from Conrad. It took a bit of work, but not onerously much, and now the nut traps are perfect. Apart from one I filed a bit too much, I'm never going to get those nuts out again.

Assemble, assemble, I know how this goes, so of course I forget to put in the nut under the motor. Disassemble, disassemble, nut, assemble, assemble. Hm, that cable looks messy - oops, I turned the entire thing 360 degrees and now the cable is twisted. Fortunately it was easier to fix this, and I took the opportunity to at least affix the cables:

With everything in, a first test just extruding into thin air looks pretty good. Time for a test piece. Today's Z offset: 0.4mm. Today's weather: Pressure 1018, humidity 63% (outside), temperature 21 (inside). Result:

Slightly overextruded still, I will need to go back and twiddle the Z_STEPS_PER_MM. That was at 0.5 extruder multiplier, trying again at 0.4 just because. Came out with really nice sides, but the top still a bit overdone. And the corners are flattened, maybe my acceleration is too high:

Doing one at 0.3 just to see how far down I can go. Cutting 25% off the material ought to be plainly visible... but no! Curiously, lowering the extrusion multiplier even more doesn't change the amount of filament used. And by now, neither does increasing it - even though further up in the log I see other values: The first (at 0.5) used 190mm, the rest used 158mm.

Interlude: Test extrusion art

Later: Mystery solved. I was setting the Z offset when I thought I was changing the extrusion multiplier, because they both ended up at 0.4. Good thing I didn't print with that.

Acceleration is actually set rather low already, compared to the Marlin defaults. I should use the M201 command to vary them.

Updated the firmware to not have a fudge factor on E_STEPS_PER_MM, and set extrusion multiplier back to 1.0. New Z offset in the evening is 1.3 (!), at 20C, 1007 pressure, 51% humidity.

And I couldn't really wish for a better print. Time to try a boat - 3DBenchy (McBenchface?) seems to be all the rage for a tougher test. Slicing it took almost 8 minutes, I suspect the slicing speed is the weak point of the Pi, and should be offloaded onto something else.

First boat print came off partway through the print:

Another try at boat didn't stick at all. Double-checking the amount of filament extruded gives... odd results. At first it's pretty close, then after more tests it becomes less and less precise, and eventually I end up with a correction factor of almost a factor 2. After that, it measures consistently correct. For now.

Another boat. The problem, now that I observe the print, is that the overhanging corners tend to curl up, and then they eventually cool down, harden, and get bumped into by the next layer. Pop! goes the print... but not this time! Bogons work.

Most discussions of curling is about curling at the bed, not at overhangs. Some suggestions are more fan (mainly), better cooling, and maybe less infill/printing faster (!). Possibly the fan blowing all over causes the print head temperature measurement to be off, which can make things really unpredictable. Maybe I should get back to the fancy fan ducts.

Some boat details:

I'm pretty sure there shouldn't be holes like that.

The first layer was more or less printing into thin air. I'm amazed it stuck.


  1. Your correction factors being close to 2 makes me wonder if your micro stepping jumpers are making intermittent contact?

  2. You mean as in inside the extruder motor, or on the controller? So various factors, including getting heated up after a big print, can change how often they make contact? When they start doing larger steps more commonly, I would get overextrusion and backpressure, leading to stripping. When I adjust for that, and they start doing smaller steps, I would get underextrusion for a while, but no stripping. My stripping hasn't shown sign of having overextrusion first, though.

    Any pointers to more diagnostics of such a problem?

  3. I don't know what controller you're on but I assume it has jumpers and you do math to get steps per mm. They shouldn't have much current at all going through them, but they are a source of power of 2 extrusion differences if incorrectly set. The weird part is that it's intermittent... I would just swap the set of jumpers on E with one of the other axes and see if it gets better.