You might find this little tool useful:
This is a block with a series of vertical and horizontal holes from ⌀1 mm to ⌀3.6 mm (nominal) in 0.1-mm increments. I print this block with any new printer / new material at the layer thickness and speed I use most often and keep the blocks as references.
Then, when I want to print a part with a hole in it that will end up printed at the final diameter without any rework (or very close, but usually it ends up exactly right) I use the gauge block I printed with the printer and the material I intend to print the part out of to find out which nominal diameter hole I need to use in the model for the hole.
For instance, the block in the photo was printed on a Prusa Mk4 with PLA at 0.2 mm layer thickness. If I want a ⌀0.8-mm vertical hole with no interference in my final part in PLA out of that printer, I'll need to model a ⌀1.2-mm hole. I know that because the shank of a 0.8-mm drillbit will slide freely in the vertical hole marked ⌀1.2 in the block.
Or if I want a hole that I can screw an M3 screw into without having to run a tap through it, the block tells me I would have to use a ⌀3.2-mm hole to fit a ⌀3-mm pin in freely, and I back off 0.4 mm to get a hole in which the screw thread will engage well but reasonably lightly, or 0.5 mm for a tighter engagement (but with a bit more risk with horizontal holes near an edge, because the layers might separate) so I know I'll have to model a ⌀2.8 or ⌀2.7 hole in the model.
I use those gauge blocks all the time. They save me a lot of time on parts that I print often because I never have to ream or thread the holes: they come out the printer just right and ready to use.
It depends on the material and printer and the orientation of the hole. Vertical holes (or up to 20 degree from vertical if they're angled) are the most accurate because you basically exploit the printer's X and Y locating abilities. Horizontal holes will always end up ovalized because horizontally they'll be correct, but vertically they can only have a dimension that's a multiple of the layer height.
With the aforementioned Prusa Mk4 printer and PLA, all the vertical small holes I print usually end up under ±0.05mm / 0.002" from the desired diameter. If the dimension is very important (for example, holes for a pogo pin holder that needs to fit with interference, otherwise it would fall off) I'll print it 0.1mm / 0.005" undersized and then I'll ream the hole just enough to get the proper fit. It's quick but not as quick as not reaming the hole obviously 🙂
Note that our printer is in a closed enclosure and that seems to make a difference for repeatability: if I leave the doors open, the diameter of the final hole varies a bit more. Nor a lot more but noticeably.
Fuck that's amazing information. I had no idea 3d printers were at that level to hold that tight of tolerances. Enough for me to look into making a purchasing proposal for a desktop 3d printer to make gages for all the warehouse pickers and packers to keep on hand for checking every order before it's shipped. We've already batted the idea of getting one to use for machine shop maintenance and repairs but the roi saving needed way too much use than avg number of repairs needed per year. Add this to those numbers tho and they would more than balance those scales to the black. Plus most of the rma cost tracking we do is projected at best so I could give the picker with the most rma's a set of gages I'll make on the mill and lathe after work. Show a month or so of zero mistake picking and bam pile on an absurd amount of operating cost savings as rma reduction potential and well be printing in no time. Really, awesome shit. Thank you.