Jeff Epler wrote: > On Thu, Jan 05, 2012 at 10:37:35PM -0600, Jon Elson wrote: > >> I just had somebody ask me about contouring performance of EMC2. >> I spotted something in the user manual I had never seen before, section >> 3.1.4, that says that no move can ever go fast enough that the machine >> cannot stop at the end of the move. This seems like it will significantly >> slow down contouring where many very short vectors occur in a row. >> > > While this statement is true about the real-time trajectory planner, it > isn't the full story when it comes to contouring with emc. > > If you have code that is of the "lots of very small segments" variety, > program G64 Pnnn or G64 Pnnn Qnnn. > http://linuxcnc.org/docs/2.4/html/gcode_main.html#sub:G61,-G61.1,-G64: > > Either of these modes enables the "naive cam detector". When 2 or more > successive motions deviate from a straight line by less than the naive > cam tolerance, they are replaced by a single line from the start of the > first segment to the end of the last segment. There is presently a > hardcoded limit of 100 segments that can be connected in this way. > Right, I am aware of this, and have used it. But, in a typical contouring job, there might be a string of regularly-spaced X coordinates and perhaps a bunch of Z coords that are bobbing up and down to make some shape. So, you can't just replace them with a straight line without destroying the detail. But, if the Z bobs are fairly small, this can be run quickly, especially if the machine components on the Z axis are light. The X (or Y) axis might be heavier. I don't do this 3D kind of stuff, so I just don't know how much of a real problem it is, or if people are picking at straws that make no sense. John T seems to indicate it really isn't much of a problem.
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