Mail Archives: geda-user/2016/01/11/06:05:48
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On 11 January 2016 at 10:47, M. J. Everitt (m DOT j DOT everitt AT iee DOT org) [via
geda-user AT delorie DOT com] <geda-user AT delorie DOT com> wrote:
> On 11/01/16 08:41, Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com) [via
> geda-user AT delorie DOT com] wrote:Surely its sufficient to draw in the outline
> your intended
> cut-out/slit/etc .. now possibly making this "Keep-out" in other layers
> may be desirable, but since you're using a milling cutter to do the
> outline, you need a path for it to follow. Perhaps you can 'shade' this
> in the GUI - I see no need for additional complexities making polygons,
> figuring out perimeters, etc, when you can line-draw and need to anyway.
> Perhaps having an outline 'layer' might help you achieve what you're
> hoping for? We've even milled curved board outlines, using the curve
> tool, and our fab. have managed this perfectly without problems.
>
The convention is usually, that you model what you want as the physically
produced, post-manufacturing shape. (This is the same with mechanical CAD
too)..
Tool-paths, drill size corrections (allowance for plating, or approximation
of nearest available drill size), are the scope of the CAM post-processor.
The reason board outlines as primitive lines on a drawing layer is not a
great idea, is that those lines are drawn with finite-thickness, leaving
the requirement of some convention for interpretation. Usually fabs follow
the center-line I believe, but possible ambiguity here is why they often
insist on the line being drawn in a small width. Due to coordinate rounding
etc.., when curves get involved, you will often find miniscule gaps between
outline segments, that the CAM system must jump over. (Not necessarily a
"problem", but an additional heuristic, and potential for error with this
approach).
This is why all the more advanced board representation formats model an
explicit outline, with poly(curve) type primitives, so an explicit design
intent of the finished shape can be modelled. This is effectively a
"polygon" shape in PCB, especially once the patches adding support for
curved edges are merged. To avoid ambiguity in interpretation, this
"polygon" needs (I believe) to be a first-class property of the stack-up
model. (Something I'm working on designing and adding currently).
Peter
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<div dir=3D"ltr">On 11 January 2016 at 10:47, M. J. Everitt (<a href=3D"mai=
lto:m DOT j DOT everitt AT iee DOT org">m DOT j DOT everitt AT iee DOT org</a>) [via <a href=3D"mailto:ge=
da-user AT delorie DOT com">geda-user AT delorie DOT com</a>] <span dir=3D"ltr"><<a hr=
ef=3D"mailto:geda-user AT delorie DOT com" target=3D"_blank">geda-user AT delorie DOT com=
</a>></span> wrote:<br><div class=3D"gmail_extra"><div class=3D"gmail_qu=
ote"><blockquote class=3D"gmail_quote" style=3D"margin:0 0 0 .8ex;border-le=
ft:1px #ccc solid;padding-left:1ex">On 11/01/16 08:41, Nicklas Karlsson (<a=
href=3D"mailto:nicklas DOT karlsson17 AT gmail DOT com">nicklas DOT karlsson17 AT gmail DOT com<=
/a>) [via<br>
<div><div class=3D"h5"><a href=3D"mailto:geda-user AT delorie DOT com">geda-user AT d=
elorie.com</a>] wrote:Surely its sufficient to draw in the outline your int=
ended<br></div></div>
cut-out/slit/etc .. now possibly making this "Keep-out" in other =
layers<br>
may be desirable, but since you're using a milling cutter to do the<br>
outline, you need a path for it to follow. Perhaps you can 'shade' =
this<br>
in the GUI - I see no need for additional complexities making polygons,<br>
figuring out perimeters, etc, when you can line-draw and need to anyway.<br=
>
Perhaps having an outline 'layer' might help you achieve what you&#=
39;re<br>
hoping for? We've even milled curved board outlines, using the curve<br=
>
tool, and our fab. have managed this perfectly without problems.<br></block=
quote><div><br><br></div><div>The convention is usually, that you model wha=
t you want as the physically produced, post-manufacturing shape. (This is t=
he same with mechanical CAD too)..<br><br></div><div>Tool-paths, drill size=
corrections (allowance for plating, or approximation of nearest available =
drill size), are the scope of the CAM post-processor.<br></div><div><br></d=
iv><div>The reason board outlines as primitive lines on a drawing layer is =
not a great idea, is that those lines are drawn with finite-thickness, leav=
ing the requirement of some convention for interpretation. Usually fabs fol=
low the center-line I believe, but possible ambiguity here is why they ofte=
n insist on the line being drawn in a small width. Due to coordinate roundi=
ng etc.., when curves get involved, you will often find miniscule gaps betw=
een outline segments, that the CAM system must jump over. (Not necessarily =
a "problem", but an additional heuristic, and potential for error=
with this approach).<br><br>This is why all the more advanced board repres=
entation formats model an explicit outline, with poly(curve) type primitive=
s, so an explicit design intent of the finished shape can be modelled. This=
is effectively a "polygon" shape in PCB, especially once the pat=
ches adding support for curved edges are merged. To avoid ambiguity in inte=
rpretation, this "polygon" needs (I believe) to be a first-class =
property of the stack-up model. (Something I'm working on designing and=
adding currently).<br><br></div><div>Peter<br></div></div></div></div>
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