Hi, I'm new to the forum and would like to help with the problem.
I use Mach3 software.
The problem is when I make a hole in the milling material, diameter 18 mm. The router makes a 21.5 mm hole. Is there any scaling in the Mach3 program that affects it. If so, how to remove it

Could you post your code? What size cutter are you using? Spiral mill or pocket?