Path of the print nozzle?

I’m printing some small parts where I want to get the size of the resulting part to be as close as possible to my target dimensions.

I draw the models in Sketchup (often scaled up for accuracy, then scaled down again before exporting), and export to STL from there, then use Lulzbot Cura v3.2.32.

In trying to work out how much if any offset to allow when sizing my parts, I’m wondering whether the slicer puts the path of the nozzle centre on the drawn edge of the model, or insets it so the outside of the nozzle follows the model edges.

My experience with Cura v2 was that I could assume that the printed part would end up about half the nozzle d iameter(0.25mm) bigger on any one side, and about a whole nozzle diameter (0.5mm) wider overall than the model.

With Cura 3.2, it seems that this is hardly happening - most parts come out pretty close to the modelled size, but it doesn’t seem quite consistent. Small holes, for example, print smaller than the modelled diameter: by more than 0.2mm, but less than 0.5mm.

Short of further experiment with a range of simple models (which I might need to do), I wondered if anyone can tell me what the software is supposed to be doing when slicing?

It sounds like the overall model size is close enough to the design size. That is good. Holes generally tend to print smaller than the design size. You will probably need to oversize the holes in the design or ream them after printing.

Thanks. I wonder then why I get different results for external and internal edges - external ones seem pretty much to size, internal ones seem to shrink more than external ones grow.