How important is the dimensional accuracy of filament relative to the detail of a print?
Yet I manage to keep my tolerances +- 0.05 mm which is enough for everything but miniature printing.
I have asked for clarification on that answer regarding what is meant by "miniature printing" but in the meantime, I want to ask the general question.
What impact does dimensional accuracy of filament have on final print quality, and why? Does it vary between different filament types?
Dimensional accuracy is not as important as dimensional uniformity. I can print with undersized (or oversized) filament, adjusting the flow appropriately, provided the filament has a consistent diameter. When creating filament in-house, without expensive equipment, it is difficult to maintain the same diameter throughout the entire extrusion. It is likely this extrusion diameter (when creating filament, rather than the output of the actual print head) to which Barafu is referring when he mentions his tolerances: +/- 0.05 mm in diameter. Which is reasonable.
The "miniature printing" comment likely refers to printing miniature models for tabletop gaming.
If the source filament becomes wider than expected, the output will have overflow, or more material than desired will be deposited, and this will certainly affect the quality of the piece.
Perhaps I should adjust the question, then? I see most PLA filaments advertised as 1.75 mm (+/-0.05 mm). Does this mean a variance of 0.05 mm in the diameter throughout the filament? Or that the diameter is uniform, and it's within 0.05 mm of the advertised diameter?
It could mean either, but most likely the first option. Your print head is likely tuned to accept a certain (small) range of filament diameters.
@LegendaryDude - it means the first of the two (variance throughout the filament). That number does not give you a degree of _certainty_ but a degree of _uncertainty_. The cases where the filament may be constantly +0.05 mm or -0.05 mm from its nominal value are just "special cases" of the more general one.