Dimensional accuracy vs. extrusion volume
Posted: Sun Jan 29, 2017 5:05 pm
I'm having difficulties reconciling getting dimensional accuracy with using enough plastic to merge together into a single solid part.
My setup: Rostock Max V2.
Upgrades: EZRStruder, Aluminum heat spreader
13-point software bed leveling calibration
0.5mm nozzle
Extruder steps/mm is calibrated to have less than 0.4% error.
Printing PLA, I was using stock settings and getting inner diameters printing 0.02-0.04 inch small. For example, to get an inner hole to print at 0.51" in diameter took CADing the hole at 0.54" diameter. External diameters were slightly large, but by a smaller amount. My extrusion value was at 103.5%. This was empirically arrived at, to make the surfaces full and flat, and each strand of plastic joined to its neighbors. My filament diameter was measured from the filament spool I'm using, and is still nicely accurate at 1.738mm.
I've tried playing with the outside perimeters extrusion width setting, but dropping it from 100% to 25% had no measurable effect.
Then I ran the dimensional accuracy procedure documented in http://forum.seemecnc.com/viewtopic.php?f=36&t=10081. Following this procedure got my 50mm and 100mm boxes within 0.005-0.01 inch, which I am very happy with. This required dropping the extrusion multiplier down to 93.5%. The problem is now that the printer isn't extruding enough plastic to make a solid surface. Even the bottom layer on the glass will have texture and gaps between strands. A single top layer is simply individual, non-touching strands resting on the infill material.
What am I missing? What other settings could I experiment with to counteract this? Right now I'm tempted to undo the dimensional accuracy calibration. This will boost the extrusion multiplier back to the level necessary to get solid prints, and then I'll just experimentally adjust any critical dimensions in the CAD until the print actually measures correctly. This means a lot of iteration through the printer, though, to get my desired results. This won't be particularly fast. It will also use up more filament than necessary.
My setup: Rostock Max V2.
Upgrades: EZRStruder, Aluminum heat spreader
13-point software bed leveling calibration
0.5mm nozzle
Extruder steps/mm is calibrated to have less than 0.4% error.
Printing PLA, I was using stock settings and getting inner diameters printing 0.02-0.04 inch small. For example, to get an inner hole to print at 0.51" in diameter took CADing the hole at 0.54" diameter. External diameters were slightly large, but by a smaller amount. My extrusion value was at 103.5%. This was empirically arrived at, to make the surfaces full and flat, and each strand of plastic joined to its neighbors. My filament diameter was measured from the filament spool I'm using, and is still nicely accurate at 1.738mm.
I've tried playing with the outside perimeters extrusion width setting, but dropping it from 100% to 25% had no measurable effect.
Then I ran the dimensional accuracy procedure documented in http://forum.seemecnc.com/viewtopic.php?f=36&t=10081. Following this procedure got my 50mm and 100mm boxes within 0.005-0.01 inch, which I am very happy with. This required dropping the extrusion multiplier down to 93.5%. The problem is now that the printer isn't extruding enough plastic to make a solid surface. Even the bottom layer on the glass will have texture and gaps between strands. A single top layer is simply individual, non-touching strands resting on the infill material.
What am I missing? What other settings could I experiment with to counteract this? Right now I'm tempted to undo the dimensional accuracy calibration. This will boost the extrusion multiplier back to the level necessary to get solid prints, and then I'll just experimentally adjust any critical dimensions in the CAD until the print actually measures correctly. This means a lot of iteration through the printer, though, to get my desired results. This won't be particularly fast. It will also use up more filament than necessary.