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<\/a><\/p>\nInitially, I looked into getting a sheet or brass or copper to make this from, but getting one that was reasonably thick (at least $\\frac{1}{8}$”) was prohibitively expensive. So my next idea was to shoot for some MDF. However, I then remembered I had some quarter inch polystyrene sitting in my basement. It’s not period, but it’s relatively easy to work with.<\/p>\n
I had about a 12″ square, so I popped a screw in the center of it going into a board, tied a string around it, and put a pen at where I wanted it and spun the styrene beneath it (much easier than trying to spin the string). I repeated this with a smaller circle for the inner ring and cut both out carefully with a razor knife.<\/p>\n
The cut wasn’t perfect so I sanded the edge of the inner disc and the inside edge of the outer ring until it spun freely.<\/p>\n
Next up came time to put the scale on the outer ring. I took a digital T-bevel and reversed the screw in it so that it went into the board<\/span>1<\/sup><\/a><\/span>. I taped the central disc back in place and worked around the edge of the ring 180\u00ba in 1\u00ba intervals (no need to go the full 360\u00ba since I don’t plan on measuring anything beneath the horizon).<\/p>\n With that complete, I removed the center wheel and, with a dremmel disc, cut the divisions with each 45\u00ba going all the way across. In addition I used a dremmel engraving tip to mark the 45\u00ba marks.<\/p>\n Since Ptolemy recommended the piece be made from brass, I gave it a coat of metallic brass spray paint.<\/p>\n At this point, I was out of the styrene and I needed a back board for the central disk to keep it from slipping through. So I picked up a small sheet of lexan and used that.<\/p>\n This was then set in the outer ring and the pointer and shadow marker applied.<\/p>\n This was all painted. To help ensure the dial was aligned vertically, I added a washer on some thread to act as a plumb.<\/p>\n I’d noted in my original post on this that getting it perfectly level wasn’t terribly important, but this was for one that was permanently mounted. Since this one will obviously be set up and taken down, ensuring it’s level each time is<\/em> important.<\/p>\n At this point, the instrument is essentially finished. I’ll still need to mount it, but for now, a test drive. I took it out and simply holding the instrument, I held it to level and rotated the central disc and sure enough, you can clearly see the shadow of the pointer hand on the other piece. (Sorry it’s out of focus. Getting it aimed, level, and taking a picture at the same time was quite hard.)<\/p>\n You can’t see where it’s aimed from this picture, but this was the result:<\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n<\/a><\/p>\n