My son is quite knowledgeable about 3D printing so asked him about his thoughts. My concerns about the inefficient airflow of a normal 3D process were confirmed by him. I will post his thoughts verbatim.
3D printing propellers is not unheard of.
When MIT first announced their toroidal propeller in 2022 (
Toroidal Propeller | MIT Lincoln Laboratory ) many people were 3D printing those because no one manufactured them - in fact I still don’t think anyone does because of the patent.
FDM can work, but not well - there is too much loss from the drag cause by the rough finish. Though, post- processing can help a lot.
Polished injection mold are the best, but if I were to try and print something like this, I’d use my resin printer with an abs-like resin, specifically
Siraya Tech Blu - Tough Resin This is the best in terms of consumer grade engineering resin. There are other more exotic ones that will perform better, but they get expensive:
Rigid 10K Resin
Props are most efficient when they are very stiff and rigid. That’s why carbon fiber props work so well. But there is a tradeoff, too rigid means brittle in a collision.
In any case, post processing the resin print for to maximize the material qualities is important if you want the best performance. This means additional UV curing in an oxygen-free environment at about 60c. This can be done by submerging the part in glycerin in a scientific oven.
One more thing to add about FDM, post processing can help smooth out the finish on decorative items, but it is not a simple task with the engineering plastics suitable for props.
Sanding can work with some materials (like wood-filled PLA, but that is too dense for a prop), but for others it takes skill given the heat from friction can warp parts and/or gum up the sandpaper. Some materials like nylon and TPU are just too tough to sand much.
Chemical vapor smoothing works well to create glossy finishes, but with only certain plastics like PLA or ABS and can lose a lot of tolerance in the process, especially with the sharp edges of an airfoil. If you really know what you are doing hand have the right PPE, stronger solvents like MEK can be used on stronger plastics - but you’ll probably melt your part in the process.
Neither PLA, PETG, or ABS I would consider rigid enough for a prop. PLA will melt in the sun, and carbon fiber filled ABS to increase rigidity won’t smooth very well.
If I had to use FDM, I’d start with a carbon fiber filled polycarbonate, and try to very carefully sand it. A P100 respirator and/or wet sanding is a must, because those carbon fiber shards in the air are dangerous.