As a first challenge I'm targeting http://www.instructables.com/id/Custom-Wooden-Train-Track-X-crossing/.

My idea is to use iPath instead to define the toolpath for the cross. The careful viewer will notice that this cross is an example of 8-times symmetry.

reflecting the above image 3 times will yield the outer boundary of the cross.

It would be nice If you can do something like:

var part = new iPath().line(3,0).line(4,4).fillet(4).line(4,0)....
part.reflect({x:1,y:1}).reflect({x:1}).reflect({y:1})

the fillet will put an arc with given radius between two straight lines:

And reflect will append itself reversed and mirrored in the provided vector.

Unfortunately I have not been able to implement reflect and fillet reliable in iPath. As an alternative for now I use an array with line points, these will all be rendered in visible line, or arc segments. This array can passed as arguments to the functions reflectPath and arcPath.