Oh boy, I keep a page just for this!.
I need to update it (for example, Arachne perimeters in PrusaSlicer now let you print extra thin perimeters), but it's useful to have a reference for common tolerances/dimensions like screw holes.
But a couple of my little additional pet peeves:
- Don't put fillets on the underside of prints (against the bed). The nearly-flat angle always droops and looks bad. Use a chamfer instead, or make a fillet that actually starts at 30° from horizontal.
- The weakest direction is between layers. Design your part such that you can print it in an orientation where the thin/weak parts aren't printed where the layer lines can snap (eg, print it flat vs vertical)
- Just like the straight lines inside screw head holes, thinking ahead in your design can prevent/minimize the need for support material. The earlier you start thinking about this in you design, the easier it will be. For example, can a part be designed with a 30° slope on an underside instead of being flat? Can you think about your print orientation early in the design process to avoid overhangs?
- Chamfer of fillet inside corners, if it's a structural part. This will greatly reduce stress concentrations.
Personally, I don't use 3 perimeters on most of my prints. On my prusa, they look totally fine with 2 perimeters. I only switch to 3 if I need the strength (which also almost always means I'm printing in PETG, rather than PLA, FWIW).
It's two-fold: lots of parking, and lack of good alternatives. If we just reduce parking requirements, but don't provide safe, reliable alternatives (eg quality public transit and bike lanes), you get angry drivers and sad (or dead) cyclists.