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Details of making custom pad shapes with polygons. [message #170270] Sat, 15 April 2017 12:26 Go to next message
David Alenhag
Messages: 4
Registered: October 2015
Junior Member
Hello.

I know of the steps to make a custom shaped pad in Eagle but I can never make one without generating "width" errors.

But I can't figure out how I am supposed to draw a polygon shape that is what I want without using a polygon width set to 0.

That is also the only way I know of to get sharp corners since if I use any width at all the corners get rounded due to the line width.

What am I missing? do you know?
How do you make a certain polygon shape that adheres to such and such dimensions while using a polygon width that isn't 0?

As far as I know I can let Eagle generate a hole load of errors and generate gerber's and have those produced and it may turn out just as I want it but I can't imagine that I am supposed to ignore those errors and even if I where they bother me(of course such things can bothered anyone but the fact that I am autistic makes those errors entirely impossible for me to tolerate), any tip or input on this would be greatly appreciated.

I saw a video on youtube which was of a quality low enough to make it impossible for me to be completely sure about the following, but it looked like that the person in that video could draw a polygon with a certain width yet the width was starting at the points that he specified and continued the specified width inwards, so that he could use a width without it ruining the dimensions of he's drawing.
But I have reviewed the entire eagle user interface for options to change so that the width isn't put equally on both sides of the points I specify as the shape but I can't find anything like that and I am hoping I am simply missing some feature or aren't realizing some simple way to do this but I am stomped.

Regards

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Re: Details of making custom pad shapes with polygons. [message #170271 is a reply to message #170270] Sat, 15 April 2017 21:33 Go to previous messageGo to next message
warrenbrayshaw
Messages: 1762
Registered: January 2010
Location: New Zealand
Senior Member
On 16/04/2017 12:26 a.m., David Alenhag wrote:
> Hello.
>
> I know of the steps to make a custom shaped pad in Eagle but I can never make one without generating "width" errors.
>
> But I can't figure out how I am supposed to draw a polygon shape that is what I want without using a polygon width set to 0.
>
> That is also the only way I know of to get sharp corners since if I use any width at all the corners get rounded due to the line width.
>
> What am I missing? do you know?
> How do you make a certain polygon shape that adheres to such and such dimensions while using a polygon width that isn't 0?
>
> As far as I know I can let Eagle generate a hole load of errors and generate gerber's and have those produced and it may turn out just as I want it but I can't imagine that I am supposed to ignore those errors and even if I where they bother me(of course such things can bothered anyone but the fact that I am autistic makes those errors entirely impossible for me to tolerate), any tip or input on this would be greatly appreciated.
>
> I saw a video on youtube which was of a quality low enough to make it impossible for me to be completely sure about the following, but it looked like that the person in that video could draw a polygon with a certain width yet the width was starting at the points that he specified and continued the specified width inwards, so that he could use a width without it ruining the dimensions of he's drawing.
> But I have reviewed the entire eagle user interface for options to change so that the width isn't put equally on both sides of the points I specify as the shape but I can't find anything like that and I am hoping I am simply missing some feature or aren't realizing some simple way to do this but I am stomped.
>
> Regards
>
> --
> To view any images and attachments in this post, visit:
> https://www.element14.com/community/message/220682
>

Hi
You seem to have a good understanding of the considerations when dealing
with polygons.

To address some of your questions/comments.

A polygon is made of wires and those wires are checked for width when
the DRC check is run so polygon wires must be of a width equal or
greater than the minimum width of wires as set in the DRC.

Because the coordinates of a wire are located in the centre of its width
you must draw the polygon smaller than the finished dimensions by an
amount of half the wire width on each edge.

As you have established, the corners will be rounded due to the end of
the wires being round. Arcs can have a square end so two arcs meeting
could have a sharp corner. In manufacturing the corner will not be sharp
as it will be bounded by the radius of the scanning beam in the lith
process. Older flash aperture processes may have approached square corners.

You have to be realistic. CAD lets you zoom in and see detail that is
irrelevant in the finished article.

The trick with polygon wire width is to make it as large as possible to
keep the size of the gerber file low, as every wire in the polygon is
another line in the gerber, and yet make the width small enough to get
the detail you need. Another consideration I try for is the make the
wire no smaller than the minimum width the manufacturer can make a
single trace. In that way you remove one more thing that their process
could trip up on.

So a technique I use when I need a polygon inside the dimensions
provided is to first draw that polygon with a width of zero on another
user defined layer. This acts as a guide for the real polygon. You can
delete this later.

Next set the grid to finest. I would use the alternate grid for this.

Then on the signal layer you draw the the real polygon inside the
guiding polygon. Use the same number of segments in the polygon as the
guide has. Use a wire width based on the above considerations. You
don't need to be accurate as you draw this polygon as it is easier to
make it perfect in a second step.

Now, using the move command, move the segments of the polygon up against
the polygon guide. Hence the finished polygon will be the desired size.

All done. Change the grid back using GRID LAST if you wish.

As for the Youtube video. I don't think it showed what you suggest.
Maybe someone has a ULP that can shrink a polygon by the amount of the
wire width it's made of.

HTH
Warren


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Re: Details of making custom pad shapes with polygons. [message #170280 is a reply to message #170271] Mon, 17 April 2017 18:46 Go to previous message
David Alenhag
Messages: 4
Registered: October 2015
Junior Member
Hello.

I wrote this post and then deleted it shortly after because I thought that I then found other threads about this and that my post would be one of those that there already exists answers for, I am so very happy you saw it though because your answer helped me very much(and those other threads didn't solve my problem at all in the end).

Finding out that polygons is made out of many lines makes the situation much more comprehensible and now I do understand why I am not allowed to use a width of zero, I read some where that a 0 width value isn't actually 0 but some fraction of a ┬Ám(can't recall exactly) and it is beyond all common sense to make a polygon with such a size obviously.

I think I am on my way away from Eagle heading for Kicad(not what I actually want to do but I feel it has become a necessity), maybe I can use the same technique there but in any case it feels very good to know of how I can deal with this situation and I have many pads to remake.

Thank you very much.

Regards

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