At 02:03 AM 9/28/2005, Leo Potjewijd wrote:
At 28/09/05 01:07, Brad Velander wrote:
I can't recall at the moment what exactly I ran into but Software
Arcs did cause me a problem at one point. Since then I never turn
them on. (Haven't seen the problem again so I have forgotten what
the precise problem was.)
In a nutshell: they mess up your clearance. Start and endpoints of
the individual segments are OK because they sit on the true arc but
the line segments in between violate your clearance, literally by
cutting corners.....
"Software arcs" suffer from the problem that they are a series of
straight-line draws. The program does not give any opinion, as far as
I have ever noticed, to control the number of draws per angular
measure. My sense, though, is that the deviation would not be great;
I'd be surprised to see more than a mil.
But I haven't, for many years, looked at this. I do know that Protel,
with small arcs, draws an awful lot of very short segments and should
not have this problem. So it would probably occur with large arcs. A
little experimentation would show how Protel actually treats the arcs
and what the maximum deviation could be. It would then be easy to
avoid the clearance problem by creating the arcs a little oversize
and then backing them off to the final value.
I liked software arcs because they are easier to import across CAD
platforms, and the data can be more easily manipulated. The RS274X
arc command is a tad complicated....
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