I realize not many people have to do this because precious metal wire is available in most countries. In Costa Rica, however, it’s a foreign concept, and we have to prepare practically all our materials ourselves. It’s not so terrible if you’ve never had the alternative, and you develop a nice bicep as a bonus.
There are two ways of pulling wire: with a machine which I don’t know the name of (I promise I’ll get a picture soon), and with your own strength, pulling the wire with draw tongs through a draw-plate. Either way, you need to use a rolling mill until you get close to the thickness you ultimately want in the half-round. For example, if you need a 2mm x 1mm half-round wire, roll the material into a 2.5 x 2.5mm to be on the safe side. Now, for that square wire to become a half dome, you need to reduce its’ thickness by half, so roll it til it’s 1.25 x 2.5mm.
The difference in procedures comes in when you choose the draw-plate to pull it from. The most common response would be to use the half-round draw-plate. However, because the dome shape has two sharp corners, it is unlikely you will get a perfect shape because the material will have trouble getting into such a tight space. You can avoid this by using the round wire draw-plate. Next, fold the wire in half, solder the two loose ends together, and using the wire rolling mill make a tip for the wire to enter the draw plate and be pulled from. Using this method, your two rectangular shaped wires will come together to form a square, which when pulled through the round draw-plate, will make two perfect half circles. Voilá!
*Always remember to anneal your wire!*