Q - How can I back up my part files.
A - Save! Save! Save! Beyond that Mastercam provides two methods
to prevent data loss, AutoSave and MCX Backup. To setup
AutoSave and MCX Backup go to Setting >
Configuration and expand Files:

AutoSave will save to your current part file name or to one you
specify at a time interval you specify or after every
operation.
MCX Backup will create a new backup everytime you save and keep
copies of older backups up to the max limit you specify.
DO THIS! DO IT NOW! You will not regret
it.
Below is an example of the back up files created.

So you will always have at least a save or two to load if
mastercam crashes and destroys your current part file.