This is the trickiest part because it requires patience and proper measurements (on your part). this is creating the face of the arc reactor. the face consists of 5 pieces; the large triangle, the smaller triangle(fits inside of the larger triangle), and the three "v" shaped pieces(that fit under the larger triangle).
i used Tupperware lids to make the cutouts. In order to get the larger and smaller triangles i went to google images and searched "perfect triangle" and then printed out the proper size triangle for the 3" arc reactor.
i was careful that the larger triangle fit perfectly into a 3" circle. and the smaller triangle fit in the middle of the larger triangle.
i cut out these parts with an xacto knife. i found that the "v's" were the hardest part. i have given pictures of my templates. it's up to you to decide on the measurements of the pieces.
once you have the pieces cut out you will need to sand them down and paint them. i used metallic silver krylon spraypaint.