Astrolabe upgrade

American University's Design and Build Lab got a new laser cutter.  Since the astrolabe I made before was drawn as a set of SVG files, I figured that it might be nice to make another astrolabe on the laser cutter.  Indeed, the result is beautiful!

This astrolabe is cut from 1/4" black acrylic with a 1/8" clear acrylic rete (star chart).  I etched the rete on the back of the clear acrylic, so there is no visible parallax error.  The pointer is 3d printed PLA. The brass hardware was hand turned on my lathe.  All of the hardware is friction fit with no adhesive used.  This astrolabe is for a fixed latitude (39 degrees North), so the center pin is (essentially) permanent.  The movement is smooth, but tight.  This is a nice improvement over my previous astrolabe, in which the hole in the rete has enlarged over time.

Unfortunately, we had trouble aligning the back.  The horizontal alignment is perfect, but it's vertically shifted by about 2 mm.  This means that the elevation scale runs off the top of the astrolabe. None of the back scales are very useful as a result, even though it is still attractive.  I think the cause of the vertical shift was an alignment key (which doubles as the ring attachment point) that we added to the front layer, but not the back layer.  We attempted to compensate for this difference, but evidently failed.  However, the compass scale on the front can still be used for elevation sighting, although this requires subtracting 90 degrees from the reading to obtain elevation.