ad astra
Right, so.. that astrolabe. I got it back a bit ago; corivax prodded me for peeeeekchures. My teacher gave me a far better grade on it than I thought it deserved, but maybe that's for effort and not execution.
I didn't just make an astrolabe. The assignment was to make something using only rivets and tabs for connections, no soldering or other heat joining. Bonus if it was three-dimensional and/or mobile. An astrolabe, by itself, is pretty much a flat disc with a spinning pointer (alidade), so I had to add something to it to fill it out. I decided upon a quadrant with a shadow square. Also found out that an astrolabe is easy to use as a relative heading finder, for which purpose it is handy to keep it horizontally level. Ordinarily, a shadow square would be engraved on the back side of a classical-style astrolabe, but marine versions have no solid back - large chunks of the plate are cut out to allow the wind to blow through it and stop it from swinging on deck. This is pretty non-traditional. Call it a Mariner's Multi-tool.
Materials used:
20ga sheet brass
21-ish ga sheet copper
14ga copper wire (shadow square wire, rivets, holder ring, shadow square plumb bob)
18ga copper wire (rivets)
Sheet of scrap mesh, used to imprint the copper
One level (plastic, I wish it were glass, but Hardwick's had no more old level parts :( :()
Brass tubing in 3/8 and 9/32" dia.
Size: 5" x 5.5"
Front side, with alidade
Back side, with quadrant. The shadow square is engraved into it in the usual orientation. The copper holder is pretty much decorative, but it was fun to make.
Did I say fun to make? I meant OMG pain in the ass to measure and cut. But y'all know I'm a masochist. Getting it to fall into place was the fun part. Drawing the plans was also a lot of fun.
Shadow squares use trig to help determine distance or height of objects. Numbers and tick marks stamped; subdivisions etched (not very deeply.)
There is a long tube rivet in the center to hold it all together. Slightly larger tubing provides clearance for the level. I tried using nylon washers for lower friction, but it was tacky and hard to form the tube rivet around.
Etching. Story and a half. Press 'n Peel was a great idea but an ultimately failed venture. The numbers are stamped, which was ANOTHER adventure. It was hard to get a deep or fine enough etch.
To take a sight, you'd dangle the astrolabe by the ring at the top, and move the alidade until you can sight a known star through both sights. The number that it's pointing to is the number of degrees that star lies above the horizon.
The alidade originally had a really pretty brushed finish, but it's started to patinate quickly in the last week or so, mrrrrt. Have no idea how to fix finishes, besides lacquering them.
Paselk's site, and astrolabes.org, are full of information and how-tos about this. Paselk linked to the book Latitude Hooks and Azimuth Rings, which I used to plan it and get the straight story on how to use an astrolabe. This book is great, if you're at all interested in reproducing old instruments; it has instructions for a nocturlabe, an octant, and a lovely perpetual calendar that looks like an armillary sphere. And about fifteen other instruments, yay! If I do another repro I want to make a miniature version of the calendar as a jewelry piece.
mmmm. fire.
I didn't just make an astrolabe. The assignment was to make something using only rivets and tabs for connections, no soldering or other heat joining. Bonus if it was three-dimensional and/or mobile. An astrolabe, by itself, is pretty much a flat disc with a spinning pointer (alidade), so I had to add something to it to fill it out. I decided upon a quadrant with a shadow square. Also found out that an astrolabe is easy to use as a relative heading finder, for which purpose it is handy to keep it horizontally level. Ordinarily, a shadow square would be engraved on the back side of a classical-style astrolabe, but marine versions have no solid back - large chunks of the plate are cut out to allow the wind to blow through it and stop it from swinging on deck. This is pretty non-traditional. Call it a Mariner's Multi-tool.
Materials used:
20ga sheet brass
21-ish ga sheet copper
14ga copper wire (shadow square wire, rivets, holder ring, shadow square plumb bob)
18ga copper wire (rivets)
Sheet of scrap mesh, used to imprint the copper
One level (plastic, I wish it were glass, but Hardwick's had no more old level parts :( :()
Brass tubing in 3/8 and 9/32" dia.
Size: 5" x 5.5"
Front side, with alidade
Back side, with quadrant. The shadow square is engraved into it in the usual orientation. The copper holder is pretty much decorative, but it was fun to make.
Did I say fun to make? I meant OMG pain in the ass to measure and cut. But y'all know I'm a masochist. Getting it to fall into place was the fun part. Drawing the plans was also a lot of fun.
Shadow squares use trig to help determine distance or height of objects. Numbers and tick marks stamped; subdivisions etched (not very deeply.)
There is a long tube rivet in the center to hold it all together. Slightly larger tubing provides clearance for the level. I tried using nylon washers for lower friction, but it was tacky and hard to form the tube rivet around.
Etching. Story and a half. Press 'n Peel was a great idea but an ultimately failed venture. The numbers are stamped, which was ANOTHER adventure. It was hard to get a deep or fine enough etch.
To take a sight, you'd dangle the astrolabe by the ring at the top, and move the alidade until you can sight a known star through both sights. The number that it's pointing to is the number of degrees that star lies above the horizon.
The alidade originally had a really pretty brushed finish, but it's started to patinate quickly in the last week or so, mrrrrt. Have no idea how to fix finishes, besides lacquering them.
Paselk's site, and astrolabes.org, are full of information and how-tos about this. Paselk linked to the book Latitude Hooks and Azimuth Rings, which I used to plan it and get the straight story on how to use an astrolabe. This book is great, if you're at all interested in reproducing old instruments; it has instructions for a nocturlabe, an octant, and a lovely perpetual calendar that looks like an armillary sphere. And about fifteen other instruments, yay! If I do another repro I want to make a miniature version of the calendar as a jewelry piece.
mmmm. fire.