Re: [CAD_CAM_EDM_DRO] High Speed Machining Look ahead EMC

> In my case I often get quite jerky motion on paths that really could
> be nice smooth curves.

Les,

Interesting that you should mention this. I've seen this, too. I just
figured it was because my servo amps have a 3ms latency between voltage
command and signal out. However, now that you mentioned it...
In my case it appears after about 1k or so lines into a contouring
program, at speeds above 40 or so IPM. It'll run great at 90 ipm for a
minute or so (G64), then stutter to beat the band. Reducing the feedrate
percentage seems improve it temporarily (i.e. set ipm to 100, reduce by 20%,
stutter reduces for a bit)
In effect it's almost like the look-ahead buffer is getting starved for
info, or it goes into G61 mode. (AMD K2-350, with 128mb ram) Does anyone
else use EMC for finish passes with large (>2mb) files, and get higher
speeds?
Z-level finishing raises the speed this happens at.

>Jon Elson wrote:
>
>These smooth corners are a string of G01 moves, not a circular arc (G02
>or G03) move? It really shouldn't stutter even on a string of G01 moves,
>though. I don't see that on my servo system. If the moves are insanely

short,

> however, like .0001" then it may have so many blocks to process before a
>decent move that the progress through the blocks is slower than the

mechanical

>movement. That is essentially bad G-code produced by the CAM package.

Well, if arc chord tolerances aren't set to 0.0001 or so, you get visibly
facetted faces on shallow curves. Thus, lots of very short moves, usually
not in a consistent plane. I would expect this to occur with most CAM
packages.
The problem with arc fitting is lost detail, especially sharp toolpath
corners. 'Dumb' optimization routines can even cause missed 'rungs' of a
lattice-work cutter paths, since it optimized out the
stepover-and-reverse-direction corner. (which are usually 90deg at a
minimum)

FWIW

Keith