An update about the process of planning to cast the bronze plates, washers (called choinikides in Greek, modiolus in Latin), linear ratchets, pawls, and trigger assembly.
I worked out the dimensions of each part in cubic inches, multiplying that number by the density of bronze, the rule of thumb (different alloys would change that slightly) being .3125 pounds per cubic inch. So, a plate 8.5” long by 1” wide at 0.125 inches in depth (1/8”) would need .664 lbs of metal, and if I make it .0625” thick (1/16”), it will be .332 lbs. of bronze. Keep in mind I need to go over the numbers quite a few more times to make sure I don’t come up short during a casting run.
Overall, I will need approx. 4.026 lbs. of bronze at .0125 thick, and half that, 2.0113 lbs. at .0625”. This is for the plating alone. Factoring in the linear ratchets and pawls and bowstring pawl, and the modiolus and associate counter-plates, we are talking about 7 lbs. of bronze, with heavier thickness components. Probably, I will go with the more sturdy parts, and factor in more bronze for spurs and gates, of course. I expect the machine will come in at around 15 pounds when completed.
As for alloys, I may use silicon bronze, but am starting to source scrap metal dealers in my area to give me perhaps better prices and increased options. I only hope the evil Breaker from the movie 13 Ghosts is not lurking around when I visit scrap yards, lol.
I will be positing photos of my melting oven when it is complete (only partially built now), but if you can picture 2.5’ tall metal cylinder lined with refractory (furnace concrete) with a hinged lid and on a wheeled cart made of rebar, you have a good idea of what the thing will look like. It will be fired with regular propane in a standard bbq tank, with a 10’ hose attached to a commercial adjustable regulator to give me up to 35 pounds of pressure, more than the standard 5 pound regulator you get on your grill. It will weigh about 90 lbs, and the basic tools I will be using will be a #6 clay graphite crucible, iron crucible tongs, iron pouring shank, safety clothing, face shield, stirring rods, etc. The molds will be green sand molds in wooden flasks. The bottom edges of the plates will be beveled inward as part of the pattern I’ll make for the parts, to facilitated creating the sand mold and to give clean plate to plate joints when attached to the machine with the bronze nails. Safety is my absolutely number 1 priority during casting, as exploding molten bronze would not be fun to be around. That would make a bow exploding on a tillering tree pale in comparison, eh
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BTW, bit of trivia: Katapeltes is the Greek word we derive the word catapult from, and means shield piercer or breaker.
