Mail Archives: geda-user/2016/01/11/06:40:20
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On 11/01/16 11:05, Peter Clifton (petercjclifton AT googlemail DOT com) [via
geda-user AT delorie DOT com] wrote:
> On 11 January 2016 at 10:47, M. J. Everitt (m DOT j DOT everitt AT iee DOT org
> <mailto:m DOT j DOT everitt AT iee DOT org>) [via geda-user AT delorie DOT com
> <mailto:geda-user AT delorie DOT com>] <geda-user AT delorie DOT com
> <mailto:geda-user AT delorie DOT com>> wrote:
>
> On 11/01/16 08:41, Nicklas Karlsson (nicklas DOT karlsson17 AT gmail DOT com
> <mailto:nicklas DOT karlsson17 AT gmail DOT com>) [via
> geda-user AT delorie DOT com <mailto: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
I do know that CAM/CNC manufacturing uses successive-approximation
polygons for curves anyway, since arbitrary circular motion is hard to
set up.
I've not used any pcb systems that are as advanced to have 3D components
and true board representation, giving you a real indication of how your
board looks, as parameters that are controlled at manufacture-time are
likely not to be available to the casual user. Most are based on a 2D
system, and then it's a matter of appropriately handling layers, shapes
and connections.
I am very interested in the effort to be able to create 'blind' vias, as
although these are more expensive to manufacture, could be helpful to
those making small pcb 'stacks'.
MJE
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On 11/01/16 11:05, Peter Clifton (<a class="moz-txt-link-abbreviated" href="mailto:petercjclifton AT googlemail DOT com">petercjclifton AT googlemail DOT com</a>)
[via <a class="moz-txt-link-abbreviated" href="mailto:geda-user AT delorie DOT com">geda-user AT delorie DOT com</a>] wrote:<br>
<blockquote
cite="mid:CAJXU7q8jzqqDkXbVXpadApYPg+YPKVPcQkR1Uq-ynJz_+XZMPg AT mail DOT gmail DOT com"
type="cite">
<div dir="ltr">On 11 January 2016 at 10:47, M. J. Everitt (<a
moz-do-not-send="true" href="mailto:m DOT j DOT everitt AT iee DOT org"><a class="moz-txt-link-abbreviated" href="mailto:m DOT j DOT everitt AT iee DOT org">m DOT j DOT everitt AT iee DOT org</a></a>)
[via <a moz-do-not-send="true"
href="mailto:geda-user AT delorie DOT com">geda-user AT delorie DOT com</a>]
<span dir="ltr"><<a moz-do-not-send="true"
href="mailto:geda-user AT delorie DOT com" target="_blank">geda-user AT delorie DOT com</a>></span>
wrote:<br>
<div class="gmail_extra">
<div class="gmail_quote">
<blockquote class="gmail_quote" style="margin:0 0 0
.8ex;border-left:1px #ccc solid;padding-left:1ex">On
11/01/16 08:41, Nicklas Karlsson (<a
moz-do-not-send="true"
href="mailto:nicklas DOT karlsson17 AT gmail DOT com"><a class="moz-txt-link-abbreviated" href="mailto:nicklas DOT karlsson17 AT gmail DOT com">nicklas DOT karlsson17 AT gmail DOT com</a></a>)
[via<br>
<div>
<div class="h5"><a moz-do-not-send="true"
href="mailto:geda-user AT delorie DOT com">geda-user AT delorie DOT com</a>]
wrote:Surely its sufficient to draw in the outline
your intended<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'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>
</blockquote>
<div><br>
<br>
</div>
<div>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)..<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>
</div>
<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, 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).<br>
<br>
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).<br>
<br>
</div>
<div>Peter<br>
</div>
</div>
</div>
</div>
</blockquote>
I do know that CAM/CNC manufacturing uses successive-approximation
polygons for curves anyway, since arbitrary circular motion is hard
to set up.<br>
<br>
I've not used any pcb systems that are as advanced to have 3D
components and true board representation, giving you a real
indication of how your board looks, as parameters that are
controlled at manufacture-time are likely not to be available to the
casual user. Most are based on a 2D system, and then it's a matter
of appropriately handling layers, shapes and connections.<br>
<br>
I am very interested in the effort to be able to create 'blind'
vias, as although these are more expensive to manufacture, could be
helpful to those making small pcb 'stacks'.<br>
<br>
MJE<br>
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