Thanks for taking the time to respond, have had a busy couple of days, will look at your suggestions and check how I set the job up, have also been mailed some vector files.
This is one off 22 pieces to be cast in aluminium to make an artwork in a park here that is about 8ft in diameter when put together. The M will have LED in it as will a few others, so will be cutting a 20mm 3/4"? piece of acrylic sheet to put in the hole. Will try a few things at the weekend, if I can sneak away from home.
Am on my phone now, but can do a screen capture of the stl file and toolpath settings.
Thanks again, really appreciate you taking time to help out