I'm sorry to have to visit this again but I have spent the last two days converting all my files back to using the R word only for arcs as Brian had said he had fixed it. On cursory inspection all seemed to be okay but as I was getting ready to machine, I zoomed in on the toolpath screen and to my horror, the -1 scaling problem has returned. I have attached a couple of screen shots that show the problem clearly. You should be able to read the code line that is creating the arc highlighted in the toolpath screen.
Incidentally, this is Gerry's (Ger) new screen set and, in my opinion, one of the best yet devised for Mach. Not released yet but looking good. Nice one Gerry.
Mike