Short answer: at least 0.8 mm for strokes and 5 mm for letter height with a 0.4 mm nozzle.
Why: a 0.4 mm nozzle makes lines about 0.4 mm wide. Two lines side by side give 0.8 mm. A stroke thinner than that can come out broken or fuzzy. Letters under 5 mm tall often fill in.
Rules of thumb for toys:
- Raised text 0.6 to 1 mm above the surface.
- Bold sans-serif fonts. Avoid thin or curly fonts.
- Put the text on the bottom or the back, on a flat face.
- Print a 10 minute test piece before the full toy.
Shapiful sets these values for you, and you can still change them. It adds embossed, debossed or engraved text to your own STL file, so you do not need to open a CAD program.
Try it on your next toy: https://www.shapiful.com/?utm_source=mataroa&utm_medium=social&utm_campaign=toys_oct26