Optimizing cutting paths, was Traveling Salesman Joke

Interestingly enough Bobcad Cam also has a built in algorithm that will evaluate chains, jump to next nearest. It is the Cut All function. It was limited to the closest entity to the origin in versions 16.1 and earlier, In Version 17, it may have allowed first entity selection, similarly to Vector. I don't remember testing it for the start point in V17. If you wanted to adjust it in earlier versions, the geometry could be displaced around the origin to control the start of the evaluation.

Probably of more importance to milling machines is the impact of tool changes and long parts.

We make some parts here that are about 2 feet long. While this is a bit larger than some hobby milling machines can cut, it really dramatizes the effects of how you make your cutting strategies. (It is small for a CNC router too.)

These parts have 6 counterbored mounting through holes, a long T-slot up the middle and they get a 45 degree chamfer on all top surfaces, and a final flycut surface. The holes are centered(spot drill), drilled, the counterbores are circular interpolated, the slot is roughed with one tool T-slotted with another and finished with another. I first programmed this by selecting the holes from left to right and generating the G-code. When I watched it cut, it was really good, while it was cutting. Because I had not paid any attention to the fact that each pass was with a different tool, each operation did a rapid for 2 feet before the next tool could start to cut. Each individual tool's cutting strategy was perfect, but they were all wrong when observed for all the processes. I finally reversed the cutting order between the spotting and the drilling, and the milling, etc, so that each tool alternated between left to right and then right to left. (Some tools did a complete circuit and returned to their start point while cutting) Because the part was so long this reduced the total running time for the part by about 30%, even though the actual cut time was the same.

I have also found that long runs **generally** are more productive than short ones. If you have 2 rows of holes, like the pin holes in a bookcase, it will usually have a shorter cut time if you follow first one row then the other, rather than trying to zig-zag between them.

Best Regards, Fred Smith- IMService
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