I have a list of small things to design and print - some of these will need to fit some other object snuggly, for example a plug in the end of a tube. I am now wondering what “precision” to model the part with. I understand the topics of printing tolerance, shrinkage, and compensation, but I want to know what precision (.e.g. decimal places) to place things when I’m modeling. This would be dictated by how precise the printing is (I don’t say “head movement” because it seems the printer will behave a little differently when depositing material that is immediately adjacent). What is the “resolution” of the A1-mini in this sense; X, Y, and Z?
Example: If I have a cylinder that needs the opposite centers of its diameter to be 19.275mm apart, after consideration for tolerance and shrinkage, can the printer actually position that precisely? If not, what’s the specification?
Another way to ask the question might be, if I ask the printer to lay down two parallel lines 10mm apart, and then separately ask it to lay down two more parallel lines that are one “smallest step” further apart, what would the difference of the inside distance between parallel lines be between examples (in this case I would assume it’s what ever the head movement limitation is)?
Print head movement accuracy is the keyword here. And this is listed for example for H2C when using vision encoder as 0.05mm.
Design as precisely as you want. Slicer will change it anyway based on selected settings, for example layer line width.
If you want more precise dimensions use STEP files and do not compress them too much while importing in to slicer. More triangles=better representation of the item.
I generally design with precision to .01mm and then test print and tweak as I need to. Test there is an occasion where I end up with several decimal places but this is not intentional.
Tolerances are affected by accuracy of extrusion flow as well as head positioning. Flow accuracy will depend on filament calibration, and filament composition (especially its water content).
The slicer may also compensate flow rates depending on whether the outer wall is an external or internal edge.
The slicer can also turn a series of straight lines that form a circular arc into the G code for an arc, which will affect the final dimensions a tiny bit.
And, as you’ve said, shrinkage can be a factor for larger parts, or parts that might warp on cooling.
I would consider 0.1 mm a sensible dimensional resolution. That’s enough to differentiate between a tight interference fit, or a snug clearance fit.