Hello,
When printing infill every 1 layers, there is no problem at all because each layer time will be about the same.
However, when printing the infill every 2 layers, the layer time will go from short on the 'perimeter only' layers, to long on the 'layers with infill'.
I have Speed overrides enabled to have proper layer cooling times, which then of course results in different printing speeds every 2 layers.
Sadly, this results in one layer being thicker than the other.
(why this happens is not really clear to me, I guess it's a combination of different things such as printing speed, layer cooling time, plastic shrinkage, ...
Anyways, it is to be expected that if you print one layer fast, and the other slow, that they will not look the same.)
I have a good example print here that shows the problems this gives.
I chose a .1mm layer height which gave a really nice result on the bottom and top part of the print. The layer are nearly not visible.
The middle section of the print (his face) had the shortest layer times because it's the smallest. (Which activates the speed overrides code)
This resulted in very visible layer lines in those areas, as the repeating layer pattern now happens every 2 layers instead of one, so it looks as bad as if it was printed on .2mm resolution.
So my suggestion would be to calculate the fan speed and printing speed, not over one single layer time, but over the average layer time of the amount of 'print infill every X layers'.
If one layer gets printed in a time which is shorter than the defined minimum layer time, that is not always a problem if the next layer is printed a lot slower. The average minimum layer time will still be correct, so that shouldn't be a problem.
