CNC wont cut curves correctly

[Sharkb8hi]

I can't get my machine to make a proper curve. They always come out as an oval and not a perfect circle or proper curve. What am I doing wrong?

[Sharkb8hi]

Here is an expanded view

I am having trouble getting my CNC to cut curves correctly. 

I programmed a circle to test the machine on cutting inside and outside a given line. the machine instead cut so the negative cavity and the piece were cut to a slight oval and not a perfect circle. Also, when trying the same procedure with an S shape the model and the negative will not go together because the curves do not align. I know my designing in the modeling space is correct and I am using a post processor from the producer of the machine which I loaded into the post library but have had similar results with other posts. The machine I am using is a Jinuan Style CNC model number STM1325C-R1. I don't know what to do and if I cant get the model to nest into a cut created for it I am going to have to take drastic action and rethink my life choices. 

Please help

[matty.fuller]

Most likely the issue is the rigidity/quality of the machine or some sort of smoothing that is applied. You may be running it too hard and fast, or there may be mechanical slop, or the control may be allowing path deviation in order to produce a "smooth" run.

You can backplot the posted code using https://ncviewer.com/ to verify it.

Otherwise you'd need to provide more info about the toolpath parameters, material, etc.