Help: My program is to long!

Heavy roughing machining

We have all as CNC operators experienced running out of program memory. CNC memory is just not very large. So we begin by deleting programs in memory until our new program fits. What if the memory is empty and there is still not enough room for our next part program? To follow is a few ideas to reduce CNC program size.

Check your program for repetitive blocks and replace these blocks with:

1.     A can cycle: All CNC machine controls have the ability to call standard MACRO’s that initiate internal code to repetitively do the same task over and over again such as drilling multiple holes and roughing an OD with multiple passes of equal depth of cut. Some examples are G81 and G73. Consult your owner’s manual for details.

2.     A custom macro: By writing your own custom MACRO utilizing the LOOP and END operators you can customize you own can cycle as described above. Your FANUC controls must be memory system B or above or this option is not available. Consult your programming manual and be very cautious to which common variables you use.

3.     A sub-program: By putting the repeated part of your code in another program it is now only necessary to position the machine correctly in the main program and then call another program (sub-program) to do the repetitive task. It is common practice to switch to incremental mode while in the sub-program and then back to absolute programming again when control is passed back to the main program. All axis movements in incremental mode must cancel each other out or a cumulative error will begin to grow. In other words; position the machine in exactly the same position you started incremental mode when you leave incremental mode.

Lengthy programs that are not repetitive:

1.     NURBS interpolation: If you are machining complex curves, CAD systems will output short line segments to generate a complex profile. This leads to poor surface quality. To create better surface finishes shorter line segments have to be used thus increasing again the length of the program. The CNC controls provides an answer for this: in your part program all you do is describe the curves using control points, control point weight and a knot vector. The CNC control calculates the axis movement from there. NURBS interpolation allows for higher feed rates and finer surface finishes.

2.    Drip feed:  All else has failed and the program is just not going to fit. By connecting to the DNC of the controls a PC can feed the controls, line-by-line, an extremely long CNC program. You will need to understand how to connect to your DNC and have the proper software to communicate with the controls. This requires much more set up than the other options and greater understanding of the machine tool on your part. Sometimes, it’s the only way.