Should I charge for design time and post-processing?

Absolutely yes. 3D design time is one of the most undervalued parts of the cost chain. If you or your team model the part from scratch in programs like Fusion 360, Blender, or SolidWorks, those hours have a real cost that must be included in the final price. The same applies to post-processing: sanding, painting, chemical smoothing treatments (acetone for ABS), assemblies, or quality checks take time and, in some cases, additional materials. A simple method is to calculate your hourly rate for design/manual work and add it directly to the base manufacturing cost before applying the profit margin.