mhotze

I've started using ABS (Innofil3D) on my first UM3 since a month, and had to fine-tuning the settings to get fairly good results. I'd like to share some insight about my last 2 prints, and wonder about the background of my observation. My second last print looked like the picture below. I've printed it with - 95 degrees heated bed, - 260 degrees nozzle, - no fan, - print speed 20mm/s - 0.8mm walls - enclosed system (door + top except for the back; I'm monitoring temperatures by the way, both near the print tip, and one of the stepper motors, let me know if this is interesting) The result is both slight warping at the first layer, but also curling of the edges of the top layer. Note that this is only the top part of the model where the model is smallest. My reasoning is that the time the layer is built is relatively short compared to the other layers with larger surface area. Therefore I concluded I needed to prevent putting the next layer onto a relatively hot previous layer. So my next setting was to adjust the "minimum layer time" in Cura from 5s to 20, and enable "lift head". I also reduced the extruder temperature from 260 to 250, since one of my earlier observations was that I has some light oozing (even with retracted filament). This resulted in solving the curling at the top of the model, see picture below: The funny thing though, is that warping did not noticeably reduce (but was not very bad either). So now here's my question: what could be the physical explanation of what's happening? It seems like curling of corners at the top layers is a different phenomenon than warping at the bottom layers. It looks to me like curling at corners is caused by relatively rapid cooling of the top of the filament, but still hot bottom part of the filament. With the coinciding bigger shrinkage of the top half of the filament, you get the curling. To prevent this from happening, I managed to get rid of this by cooling down the previous layer enough, to get more evenly cooling down of the filament that is layed down next. The weird thing though, is that for preventing warping at the bottom, the general advice seems to be to get the heated bed close to the glass temperatures (for ABS this is 105 degrees). This is more or less the opposite of preventing curling at the top, where the previous layer needs to be cooled down enough??? I wonder how this works, or maybe I assumed wrong somewhere. The only thing I can imagine is that curling of the top is caused by the previous layer still being above glass temperature, and also curls up a bit since it's still deformable. If this is the same phenomenon as warping at the bottom, then this would mean that having a bed temperature near or above glass temperature would enhance warping instead of reduce it?