- 1). Make the frame first. To do this, cut the angle iron into 12 1-meter pieces using a reciprocating saw. These pieces will eventually be used to make the three curves of each of the four sections of the mold. Cut the remaining angle iron into eight 1.2-meter pieces. Each of the four sections of the mold will eventually use two of these pieces.
- 2). To bend the angle iron, begin by drawing a circle -- with a diameter of 130 cm. and a radius of 65 cm. -- on a flat cement floor (or another flat surface) with a marker. Bend the 12 1-meter pieces of angle iron to conform to the curves of the circle. The iron should never be twisted; it must lie flat to achieve a smooth curve. If you bend the angle iron correctly, you should see one flat edge facing down and the other edge should be facing out.
- 3). Create each of the four sections separately using a welder. Weld two 1.2-meter pieces of angle iron to the three bent pieces of angle iron (the top, middle and bottom). You should use 1.5 sheets of sheet metal per section. Keep in mind that the top has to have the flat side up and the bottom has to have the flat side down. The middle piece of bent angle iron should be 60 cm from the bottom. You should only weld six joints on each section, but on each joint, you should weld four places. The angle iron is simply overlapped to make lap joints, which makes it stronger than just two butt joints.
- 4). Attach sheets of aluminum to the frame with pop rivets. Each section should use one full sheet metal (1.2 inches tall) and another one that is ripped lengthwise. To rivet the frame and aluminum together, drill holes through them; use one pop rivet every 10 cm. Be sure to use medium-sized and medium-length pop rivets, keeping in mind that the pop rivets may have to pass through two layers of angle iron and the sheet metal. Each section of the mold should use a little more than one piece of sheet metal. To keep the outside edge of the mold smooth, attach a factory-cut edge of the patched piece of sheet metal to the angle iron. The rough edge of the patched piece should be tucked behind the factory-cut edge of the uncut piece of sheet metal.
- 5). Drill holes in the upright pieces to bolt the pieces of the mold together. These holes should be 10 cm from the top, 10 cm from the bottom, a little off center, and have enough space to easily tighten and loosen the nut. It is best to use six 3/8-inch bolts that are 1 inch long as well as two 3/8-inch bolts that are 1.5 inches long.
- 6). Permanently mark the sections of the mold by welding points into it or drilling notches into it.