Mechanical stacking
-------------------

From the bottom to the top, we have the following elements:

- Ben case, bottom shell
- a few drops of glue or silicone, to hold the counterweight in place
- the counterweight, covered by protective paint
- a few drops of glue or silicone, to keep the cover sheet in place
- a cover sheet of thin hard plastic, e.g., the type of plastic film used to
  make transparencies
- isolating tape, applied to tall components of the Ben's main PCB
- the Ben's main PCB


Protection
----------

The counterweight is covered by one or more layers of paint, to prevent
direct skin contact with the lead during handling. The paint may also
offer some amount of protection against electrical contact.

The counterweight is covered by a layer of hard plastic that isolates
from electrical contact and that also resists being punctured by pointy
components or solder joints of the main PCB.

Finally, all elements on the main PCB that are unusually tall are taped
over, to further reduce the risk of them working their way into the
counterweight. Right now, the only component where problems are
considered likely is the buzzer.


Workflow
--------

- analyze geometry, e.g., by viewing ben-bottom-inside-500um
- define CAD model in cw.py
- generate in HeeksCAD with "import cw"
- define Zig-Zag operation
- generate Python script and run it (takes a while)
- save NC file
- convert G-code to gnuplot, with cncmap/g2gp
- mount piece and determine geometry with millp
  (from http://svn.openmoko.org/developers/werner/cncmap)
- define conversion in "doit" script (to do: put in repository)
- ./doit >job
- send job with cncmap/spool