Triffid's temp calibration & infill extrusion width?

Currently suffering with poor overhangs on the hull of the 3DBenchy and suspect my answer lies in needing some part cooling, but also thought a too high extrusion temp wouldn't help. I tried the following the nozzle temperature set up guide in the following link:

[reprap.org]

I made a test part that was a constant 30x30mm square profile and used 20% infill. I ran the build and varied the extrusion temp as directed. Started on about 190 and varied it up to 220 and couldn't get rid of the broken/incomplete (dotty?) infill. I tried dropping the temp and that had no effect up until the point where the printer stopped extruding because the nozzle temp had dropped below the minimum extrusion interlock temperature.

I only started to get good infill after stopping the process and re-preparing with a 0.7mm infill extrusion thickness rather than the 0.5mm that the default setting chose.

I'm running PLA with a 0.2mm layer thickness and 0.4mm nozzle. Infill print speed is set to 60mm/sec.

Any hints or should I just drop the extrusion thickness from 0.7 until it looks crap again, add a safety margin, and run with that? Any other temperature calibration guides?

What infill pattern are you using?

If you use "rectilinear" or "lines" the infill goes in one direction per layer, so the infill on each layer only contacts the previous layer's infill at the points where the lines cross. That means the infill lines are bridging all the time. You may have bridging flow and speed set to values that aren't working well. You can adjust those in slic3r and probably in Cura, too. If you use "grid" or "triangles" or almost any other infill pattern, there is no bridging and the infill should come out better.

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Ultra MegaMax Dominator 3D printer: [drmrehorst.blogspot.com]

Ahh good shout! Yes, slic3r revision 1669 running rectilinear infill. No idea what bridge flow ratio is set to. Wouldn't take much of a drop to reduce the ideal extrusion diameter from 0.5 to below the width of the nozzle.

Just had another crack at this. Reset the extrusion thicknesses to default and used an aligned infill pattern. This is single direction lines, no bridging, and no crossing. Had a couple of broken lines but never really saw dotty. Raised the temperature from 165 up to 210 in 5C steps leaving 2.5mm on each temp. Never cured the broken infill lines but did spot something interesting at the start of the perimeter. On the higher temps there was a gap just at the point the extrustion was supposed to start. This cured when I dropped the extrusion temp back down to 165C.

Just tried the 3DBenchy again with lower temperatures on bed and extrusion and still getting the perimeter curling up on the bow a few mm up in the build. Think I need to prioritise getting the part fan connected!