It's finally starting to look like a stargate. I finished cutting out all the plastic pieces, like these chevrons here:

I then tried fitting everything together. Of course nothing was perfect the first try, so I carefully shaved down the imperfections till the rotating ring moved freely. Here is a rough diagram of the assembly. It consists of four layers stacked like so. You can see that the back is closed and undecorated, but hey, that's how they made the actual prop in SG-1. They never show the back of the Earth gate for a reason. 

And here are some pictures of the layers just sitting on each other, not attached. Trust me, it will look a lot better when it is cleaned up, painted and illuminated. But before I do that, I will work out the ring moving mechanism. I'll update again after I get things moving.