I'm a noob here so perhaps this or something close has already been suggested. I was thinking for infill that the layer could be printed at double the thickness of the shells and then it would only have to be printed every other wall layer. Could speed things up a little. The infill doesn't have to be anywhere near the quality of the walls so printing it twice as thick could be just fine.   While I'm thinking about it, maybe the option to print layers at changing thickness wo