This seems to be a long-running issue for us all: Parts Too Big and Holes Too Small
I was looking this up this morning because a gap between parts I cut yesterday that should have been 15mm was 13mm and I had to “sand to fit” as well. 2mm is a really big difference when I can run an engraving to an accuracy so small I can’t measure an error. I’m using Estlcam for the CAM.
Had this problem drilling dog holes too. Holes were too small.
There are a lot of variables at play…Actual bit size, deflection, etc. There may be something in the finishing pass treatment, too.
Things to investigate but no silver bullet it looks like.