A CNC machine is not always operated by the means of a program. During part setup, the CNC operator has to do a number of operations that require physical movements of machine slides, rotation of spindle, tool change, etc. There are no mechanical devices on a CNC machine. The handle (Manual Pulse Generator) is an electronic, not a mechanical unit. In order to operate a CNC machine without conventional mechanical devices the control system offers a feature called Manual Data Input – or MDI.
Manual Data Input enables the input of program data into the system one program instruction at a time. If too many instructions were to be input repeatedly, such as a long program, the procedure would be very inefficient. During setup and for similar purposes, one or a few instructions at a time will benefit from MDI.
To access MDI mode, the MDI key on the operation panel must be selected. That opens the screen display with the current system status. Not all, but the majority of programming codes are allowed in the MDI mode. Their format is identical to the format of a CNC program in written form. This is one area where CNC operator acts as a CNC programmer. It is very important that the operator is trained at least in the basics of CNC programming, certainly to the point of being able to handle the setup instructions for Manual Data Input.