[Bisorcam]

How do I know which CNC to pick for my default to use.

[txcncman]

You know which one to pick for default based on which machines you have on you shop floor and which of those you have set up in the Machine Definition Manager and which of those you wish to be the default machine.

If you were asking where in MasterCam you set the default machine, that is done in System Configuration under Default Machines. (See attachment.)

[Bisorcam]

I'm confused about the part where it says at the end. Example is : mm.mmd.vmc. Hmc

What do those mean ?

[txcncman]

Do you know what file extensions are?

mm is for millimeter (Metric based machine) and should not be used as a file extension.

mmd is for Mill Machine Definition and should be one of the file extensions used.

vmc is for Vertical Machining Center and should not be used as a file extension.

Hmc is for Horzontal Machining Center and should not be used as a file extension.

Have you read any of the MasterCam help file or documentation?