I use three layer thicknesses for my nose cone3D prints; with a 0.4mm extrusion nozzle diameter that translates into 1.2mm wall thickness (about 0.05 inch). I found that 2 thicknesses were not strong enough especially at the shoulder joint of the nosecones. The 3 layer wall thickness is strong enough to resist breakage at the shoulder joint when sanding prior to painting. I am using PLA filament which seems to be very crystalline making it very tough material to sand.

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Bruce S. Levison, NAR #69055