[Pcb2gcode-devel] PCB Board Expectations

[Ford P. <fo...@hi...>]

Good evening,

 

I'm new to this forum.  I'm trying to diagnose some problems with this GCode
conversion tool.

 

Using KiCAD for circuit board design and layout, I'm able to extract Gerber
files.  Pcb2gcode converts them for running LinuxCNC under Ubuntu 10.04 LTS,
which is the most recent stable version for running LinuxCNC.  My router
table seems to be able to reliably hold a repeatable trace.  I have several
concerns and am hoping this list can provide some reliable answers.

 

While the spindle on my CNC is light duty (a ball bearing dremel tool
running a 0.1mm 60 degree V bit).  I have a new spindle on order and may not
see it for another week or so.  Adjusting the Z axis to obtain a cut
sufficient to remove copper, the narrowest insulation I can obtain with this
0.00397" V bit is about 0.030" using a micrometer.  Thinking this through,
am I observing the run-out in the bearing at being roughly 0.026" ?
Inspecting the spindle I simply cannot believe there is that much play.  I
would certainly expect to visibly see 0.026" of play and I'm unable to
observe ANY play in the spindle at rest.  While I was expecting some play, I
was not expecting this much.  Are my expectations unreasonable?

 

Using a test circuit called TraceTest I've installed nine SM1206 resistor
footprints and connected them in series using trace widths ranging from
0.018" to 0.042".   I convert the Gerber to GCode with the following command
line:

 

pcb2gcode --front TraceTest-Front.gbr --zsafe 0.08  --zchange 1 --mill-feed
6 --zwork -0.08 --offset 0.002 --mill-speed 20000

 

Even though the Gerber files were produced by specifying a 0.004" bit, a
0.004" insulating band, pcb2gcode insists on retracing the board a second
time.  After a first pass, a 0.042" wide trace remains but only about 0.010"
wide.  The second pass obliterates the traces and the pads.  I either do not
understand the offset attribute or my spindle is simply a POS.

 

I do not see an attribute for bit size.  Only the -offset, which I've set at
0.002" (half the bit size)  It seems the second pass enlarges the insulation
by taking part of the trace. I experimented a little with a negative offset
and saw no real difference.

 

If someone could help me diagnose my issues, I appreciate it.

 

Ford