Re: gEDA-user: Comments on pcb's g-code exporter & HeeksCAD/HeeksCNC FOSS program for pcb milling

[Markus Hitter <mah@xxxxxxxxxxx>]

Am 11.11.2010 um 05:11 schrieb dfro@xxxxxxxxx:

> I like that the gound plane outline is machined. The circular pads  
> could use some more lines to round them out. Have you thought about  
> programming g-code arcs (G02, G03) for them? HeeksCAD/CNC does this  
> (see below).

Using G02/G03 isn't trivial, as the isolation milling paths aren't  
calculated by offseting all the existing lines and pads by some  
geometric calculation, but by drawing all the traces, widened by the  
tool radius, to a pixel-based intermediate image, then figuring the  
required paths from there. All this algorithm was done by Alberto  
Maccioni and some research brought up the statement, this is the only  
reliable way for offseting all the traces. Doing exact offsets is  
said to fail in edge cases.

If you want more precision, you can raise the accuracy, which is set  
to 600 dpi = 1.7 mil by default.

> Having a dxf file allows people to tweak all of the milling  
> variables (depths of cut, jogs, feed rates, number of passes,  
> pocketing, drilling, etc) in a CAM program, rather than go through  
> the g-code by hand.

Except for multiple passes and clearing out pockets completely, this  
functionality exists already. Feed rates have to be hand-edited in  
the resulting file currently - a single spot near the top of the file  
- but this is a subject to change soon.

A few tests with Eagle's G-code exporter using multiple passes show  
results worse than with a single pass, but your mileage may vary  
here. You need a really stiff and precise machine for such things, as  
the typical engraving tips are more pressing the copper aside than  
really cutting it.

An DXF exporter would be an entirely different exporter and good luck  
finding an algorithm to connect all the lines and circles together.

That said, you can use the PostScript exporter and load that into  
Inkscape. Create an outline path for all the lines there, stitch  
everything together and export it to G-code with Inkscape's G-code  
functionality (an add-on) - and you'll soon be happy with pcb's G- 
code exporter als any attempt via the DXF route is a lot more work. :-)


Markus

- - - - - - - - - - - - - - - - - - -
Dipl. Ing. (FH) Markus Hitter
http://www.jump-ing.de/







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