Given the diagonal formed by the sides of the mirror box, the diameter of the mount needs to be 32″. I cut the two circles of the mount out of 3/4″ ply and 1/2″ OSB. I also cut the two vertical, altitudinal support pieces out of 3/4″ ply. At CCCC we cut a ring of Formica 4″ wide, and two 1″x 45″ strips for the altitudinal bearings. The excess width on the bearing strips I route red off, once they were attached with contact cement and allowed to dry over night with a strap clamp.
The lower disk was finished with wiping varnish (2:1, varnish to spirits) as was the bottom side of the upper disk. The upper side of the upper disk and the supports for the altitudinal bearings are finished in a varnish-oil (2:2:1, varnish to BLO to spirits).
2015 01 20. I joined the two azimuthal disks. I used a 1/4″ x 3″ bolt with a washer from above, a spacer in the upper board, a t-nut in the lower disk. I used three pieces of teflon, 1 5/8″ squared, #8 x 3″ cabinet screws, and three inch pieces of 1 1/2″ diameter dowel. I bored a hole with countersink, and attached the teflon pads with the screws through the lower disk and into the dowel feet.