Tuesday, February 16, 2010

Welcome to the Machine

Or welcome to the machines as it were. I think there were four Excellon drilling and routing machines at C.F.C. One of them had just a single head and was used for making first pieces to test for errors in the drilling and routing programs.

So my first job was to learn the programming language for these machines. Bob Spain and a young lady named Kristen Van der Laan were my teachers. This is no high level programming language, but more like a machine code of sorts. Circuitboards are still drilled and routed this way today more than 20 years later.

Here is an example of a very short Excellon drilling program. The actual language for CNC machining is based on commands used to control Gerber Scientific plotters:


That drills just three holes of two different sizes. Writing programs to drill holes wasn't really the engineer's job. We mostly wrote programs to cut the boards out. Most of these were simple rectangles, and the program for this wasn't much longer than the example above. Sometimes boards would be circular, or have odd shapes. Some would have chamfers, fingers, slots, large inner cutouts. There was great variety. Sometimes we would make palletized panels which have more than one circuitboard. The routing was designed to leave only small perforated spots to hold it all together, and the boards would be removed from the panel either by hand or by machine.

We would write a program for routing using WordStar and then save it to a floppy disk. Then we would send the program out to the paper tape punch machine. The tape was usually gray, blue or pink. There were little tiny round pieces of colored paper all over the place.

A finished program would go out for a first piece to make sure it was correct. If you left just one digit out of a routing program the machine could destroy the panel, cutting straight through the middle of it.

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