mastercam comes with several editors and some can file transfer normally by rs232 null modem serial port cable. i usually use a laplink cable.
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basically you have to set computer and mastercam editor up with correct communication parameters for example
com 1
4800 baud
7,n,1
each machine is different thats why you need cnc manuals so you know what to use.
then you put cnc in a mode expecting the file transfer, sometime it wants the file given a name. the cnc usually has no ideal what the file name was originally on the computer, normally you tell the cnc that the file about to be transferred is to be named what ever you want. some cnc have file name limits for example file name might only be numbers. or letters and numbers but a limit a 8 characters long with no spaces.
..... then mastercam editor you send (usually it is just send and not send file) they are not the same. send just sends ascii text
....... after sending a short file try a dry run with no tooling and see if it looks right. often you might have to send back from CNC to mastercam editor that is in receive mode to see if some error occurred in sending file.
........if post processor used in mastercam is not correct one the cnc may stop in the middle of a run with a error message. you again need the cnc manual to understand the error message