Ok.update on this so far. The mach3 software is my own. The proxxon mill cuts to scale on all the test g codes to set up in mach3. The over upscaling comes into play when I used g code written by art cam express and used this program to post the g code in mach3 tap format. Using a cam edit software to view the g code turned up know errors.but mach 3 did not like the code and upscaled the work. To make sure it was not the mach software at fault I used an old test g code which resulted in the mill cutting the design correctly..at the moment it looks to me like the fault lays between the art cam way of writing g code and mach3 reading the art cam g code.
I am going to try a second program later today to write the g code.Will post how I get on later this week.