I've been battling with a small PETG print. The top features is a round pin about 5mm in diameter. I've got the settings dialed in nicely for the larger lower sections of the model, but when it gets to the pin, it makes a mess. The defects were consistent with the previous layer still being molten and getting dragged by the extruder when the next layer got printed.
I've been running the majority of the print with no cooling. The pin section takes about 7 seconds to print a layer, and I had the "Increase fan speed for layers below" set to 5 seconds and 60% cooling.
I went in and forced the fan to come on at the layer where the pin feature starts. I tried 45% cooling and 75% cooling, and they both made a HUGE improvement in the quality of the print, with 75% being slightly better.
Here are before & after pictures of the pin (the model has been chopped down just to test this issue):
I haven't verified this visually, but all indications are that the "Increase fan speed for layers below" X seconds setting isn't doing anything. Is there some weird issue with starting with 0 cooling, or am I missing something else? From what I can see, this looks like a bug. If not, then what am I misunderstanding about this feature?