"Wheel" Mariner's Astrolabe

"Wheel" Mariner's Astrolabe

In 2015 I modified this early effort (photos above) to model the earliest "open-form" or "wheel" mariner's astrolabe so as not to duplicate the new heavy cast model I made in 2014. It was originally made as an interpretation of a mature Spanish/Portuguese design, c. 1560–1800. The model was derived from a photograph of two instruments in a book about early scientific instruments and instrument collecting (Michel, H. [1967]. Scientific Instruments in Art and History. New York: Viking Press). This was my first attempt (1985) at an early instrument model.

The body was fabricated from ¼” bronze rather than the heavy (3/4") casting of a real instrument. The bronze used for the instrument body (4) and alidade (1) was from a discarded grave marker, approximately 1/4" in thickness. The original beaded pattern on the top of the marker can still be seen on portions of the instrument, the letters and numbers on the original marker were ground off. As can bee seen in the image of the reverse (top right photo above), the instrument was laid out on the back, ground side, of the marker (note the remaining patina and salts on the casting, the result of its prior existence in contact with earth). After layout, the instrument parts were cut out with a jig saw, and finished with files. The sights on the alidade were fabricated from 14 g brass sheet, with site holes carefully drilled so they would align with the filed "knife" edges of the alidade. They were then soldered into file-cut grooves in the alidade with rosen-core tin-alloy solder. The hanger (3) was made from a bronze eye-bolt I had in my stocks, while the connector allowing motion in perpendicular directions was fabricated from another small piece of the marker bronze. This early effort was graduated using a good quality drafting protractor and scribed on circles cut with a large divider. For the "pin" I used a 1/4" 20 bolt and a custom made nut I fabricated from brass rod on a lathe. 

In 2015 I used a jigsaw to cut out the "weights" at the bottom of the body and then cleaned up the new cuts with files.