Different speed when part is duplicated

[kylefaucett]

I've been using the default ABS and STANDARD slicing profiles from the SeeMeCNC download page, which have been working well. After several prototype iterations for a part, I duplicated it to print five at a time. When I print five at once with the same settings, suddenly the printer is moving and extruding much faster. The ratio of extrusion to speed appears to still be correct, but it's going too fast for the quality and tolerance I need. I reloaded the 1-up and 5-up STL files and regenerated the gcode to double-check.

Is this a bug or am I missing something?

[IMBoring25]

It must be a fairly small part, because this makes sense if the minimum layer time in the slicer is driving your print speed when you're printing one at a time. If you need lower baseline print speeds, slow down the baseline print speeds.

[kylefaucett]

That's it - thank you! I thought I thoroughly looked through the settings for anything that would be affected by the size of the print, but I apparently missed this: Filament > Cooling > Slow Down If Layer PrintTime Is Below: 40 seconds. I set that to zero seconds and printed a 1-up part, and it printed at apparently the same speed as the 5-up print.

Now I'm inclined to do my 1-up testing with that setting at zero seconds so that I can count on similar results when I increase the number of parts printed at a time. However, I can see the logic behind that setting: make sure one layer has enough time to cool before printing the next. That begs the question whether my tests will still be valid enough without having to waste plastic bulking up the print size as I go through design iterations. Maybe the ideal solution would be to retract the filament a bit and just pause at the end of each layer, so that the speed during extrusion remains constant.

[IMBoring25]

You can put a dwell in after every Z move but it may result in more ooze/blobbing issues and you'll have to consider that in your evaluation of the results. You could also build something sacrificial that's smaller (i.e. uses less filament) at the opposite corner of the build plate.