Quote Originally Posted by Neale View Post
If I now take cuts on opposite sides of a (roughly 50mm) block to produce two parallel faces and measure them, there is a consistent error of about 0.3mm. Even though I have checked machine movement and cutter diameter.
Try that with machinable wax or another material not strong enough to flex your machine's structure, there is a strong possibility that your machine is flexing under the forces applied by the test cuts.