SimpleScott wrote:
My settings:
Extrusion temp: 235C
Bed temp: 90C (This is PEI, with Uhu glue stick applied)
Fan: Off for layer 1; On at 35% for layer 2+
I know this is an old post, but I've been tweaking 910 recently so I thought I'd add my 10c.
I'm printing a large part, it barely fits in my TAZ6. The 235C/90C is Cura's standard settings and they worked well on the herringbone gear (I replaced mine with 910 ones, too.) However, when I used the same settings for the large print, it was a complete failure. Layer adhesion was terrible, I could basically push my finger through the walls. I'm not sure whether the material got cooked sitting at 90C for 36h or if 235C is just too cold on large prints where it has time to cool completely between every layer.
Taulman recommends 250C-260C and the bed at 45C, and no fan. When I use that, I get an incredibly strong print. The one problem is upcurl at overhanging edges which grow until either they get reanchored or the angle changes or the nozzle snags on it and the print fails. This problem also seems to get worse with long layer times. The solution here was to increase both extrusion width from 0.5 to 0.6mm and layer height to 0.25mm. (0.3mm layer is even better, but then the space to the supports is too large and I get loose loops of plastic on nearly-flat overhanging areas. 0.25mm was a good compromise.) I also used the "use bridging for perimeters" setting in 4.0 to turn the fan on only for the overhanging perimeters.
Supports needed 2 layers spacing on bottom layers to not completely weld themselves to the part. 1 top layer worked fine, and 0.5mm horizontal spacing worked well.
The final piece of the puzzle was to make sure large overhanging areas have some support to hold them down. I found I could use a 70 degree support angle if I made sure to add additional supports on convex, overhanging edges where the upcurl starts.
With these settings, the print comes out very strong and almost flawless and the supports are well adhered yet pop off cleanly without marring the part. (There are just a few zits on the inner surface, the only thing that was better at 235C was that there was less ooze, but that's less important to me than the strength of this part, they come off cleanly with a knife.)
Judging from the look of the original post, it looks like upcurl on the overhanging edges to me. The dark deposits are the tell-tale sign that the plastic is bending upward and brushing off cooked material stuck on the extruder. It's possible this part is small enough that some fan is needed to hold the material in place. (Taulman says no fan should be needed unless the part is < 10mm^2, but I think that depends on what it looks like. For those overhanging edges you may have to sacrifice some layer adhesion for detail.)