I had trouble with fit at first. I think there are many topics about “parts too big, holes too small”
A few calibration cuts and what I found was that telling my CAM that my 1/8" (3.175mm) nominal bit has a cutting diameter of 3.0mm gets me a consistent fit. Parts fit into slots, dovetail joints fit, and part size accuracy stays good.
I cut 3 squares, inside and outside. 50mm, 75mm and 100mm. (What I could use calipers on.) None of the outside cuts fit in the inside cuts with the tool defined onside dimensions were small, outside dimensions were big. My conclusion was that the bit is cutting a narrower than nominal kerf, so I adjusted the tool definition to reflect what I saw. I rounded the 3.0 something something to just 3.0 and it works. I use 2.95 for some very soft woods or a looser fit. Even if hard and stable materials can be better, and might work closer to 3.175, it’s close enough for the tolerances thst I need. I did that a few years ago, and it still works.
Yeah, I also wanted joints to “just work” and… now they do.