[Melodica-Me]

I have to agree with Tatu, when the piece is milled it should be flat and true when the final cut is completed. Unless the end mill is heating up the material enough to distort the material as it is cutting, then once the material cools down the true cut will then be visible. Also if the original material used is not flat or is held down with different pressure points, this can create uneven cutting surface as well. Parts that do not sit firmly to the bed will over cut or push the material as it cuts and create an uneven surface too. Another issue is that when cutting polymer/plastic/acrylic from one side only can cause a bowing effect due to heat stress build-up on one side only.
Melodica-Me