n00b query, please help - joining lines, indexes and culling

Hi Guys,

This is my first post and my first attempt using grasshopper. I'd like to think this is OK so far, but please tell me if/where you think I have gone wrong.

The gist of this is its a vented housing for an LED PCB. The object is a parametric series of discs with an opening inside made up of a mirrored curve [drawn in Rhino, mirrored in GH]

It is madde up of N number of discs which can be varied through the distance between the circular outline using a divided curve [straight line in GH]. The length of the object can be varied using a length parameter, and the shape using a graph mapper.

I've chosen to cap the end two discs by creating two sets of outlines. One set has the central aperture cutout for the PCB, whereas the other set is a trimmed circle [achieved using the "trim box" layer profile in Rhino]

I then cull the outer two curves from one array, and the inner N-2 curves from the inner array.

The final outcome I am after is to create the housing as both an STL and a 2d template for laser cutting. This is a learning exercise for me as well as a cool project.

I had it working OK, but then I adjusted the profile for the PCB and joined it and now it is giving me some grief. I am sure the answer is obvious. The problem is the PCB profile is made up of 3 polycurves, whereas the disc profile is one planar curve. I have no problem using the flatten option so there are only N sets of curves coming out of the "Join Curves" component. However when I cull the curves, the planar curves making up the exterior edge cull fine, but the interior curves [the joined, PCB profile] culls in a different [irrational?] order to what I would expect. If I connect the single planar curve to the culls section, it works fine, but the joined line section just won't play.

In the instance uploaded N = 10, based on spacings. And index white it appears that 0 and 9 are diagonal to what I'd expect, although if you fiddle with the values they go all over the place.

Can someone please help me and explain what I did wrong? Files are attached... I have screen grabbed the relevant section, but it is grouped in red and labelled as "problem child" :)

Many thanks for your help, sorry if this looks like a clusterf**k, first time for everything... any advice very much appreciated, not just relating to my problem. 

All the best

Nick