Re: gEDA-user: comments on pcb's g-code exporter

[<jbump@xxxxxxxx>]

> > On page 1 of the LPKF brochure (http://www.lpkfusa.com/datasheets/ prototyping/rp_brochure.pdf ), it shows a screenshot of their pcb artwork software. The thick grey traces are used to route the border of the part. I noticed the breaks in the trace in order to create attachment tabs, which you can see in the picture to the right of the mill making some boards. You could have a field in the g-code export window where you can choose a layer from pcb, which contains the traces for the border routing operation. The user can customize with a simple series of thick (or thin) traces exactly what shape they want the pcb border to be, i.e. with or without tabs, what diameter endmill to use, etc. 


> This layer is there already, it's the one named "outline", all lower  
case. What isn't there is code to calculate the offset of the lines
and polygons on this layer, as I couldn't find existing functions in
the remaining pcb source code and I lack the resources to write it
myself.

I use Circuit Cam to convert gerbers into LPKF files.  It works quite 
well: offsets are all okay so everything shows up superimposed.
One thing I found that might be useful to anyone else doing this 
(which should be most people using an LPKF since they supply Circuit 
Cam with the machine controller) is that CC doesn't correctly import 
gerbers from PCB because PCB (kindly) includes a layer name assignment 
in each gerber, with a line like:
%LNFRONT*%
about 10-15 lines from the start.  CC imports this into a layer called 
FRONT even if you instruct it to assign that film to CC's TopLayer, and 
then can't find the objects when it tries to insulate it.
Delete the line in each gerber and it'll import correctly.
Likewise, I have an OUTLINE layer and that imports into BoardOutline 
and CC correctly assigns that for outside cutting (once I delete the 
layer name instruction.)
This is CircuitCam's problem, not PCB's, but that's the quickest 
workaround I've found.

By the way, the tabs idea in the original post won't work.  From the 
original post: "it shows a screenshot of their pcb artwork software. 
The thick grey traces are used to route the border of the part."
The gerber has a board outline.  Once you process it in CircuitCam, CC 
produces the gray trace as it calculates the centerline of the router 
you choose, so that feature is CC-dependent.  (It'll be a different 
routing path if you're using a 2mm router bit, rather than the standard 
1mm router bit.)  The board outline is all you need to give to CC.  
Breaking it up into segments is going to give CC some troubles because 
it will calculate a route that surrounds all the outlines -- in other 
words, it will calculate a cutting-outside route around the 
circumference of every line segment, meaning it'll route into the 
inside of the board, leaving nothing but a nice 10 mil wide border of 
copper around the outside of your board unrouted.  So that's not going 
to make shaker tabs like you want.  (I tried this, is how I know.)
It'd be nice to know how to produce tabs for the LPKF through Circuit 
Cam, so if anyone has run into this I'd love to know.



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