Step 5: Machine the main tubes
- The 3 main tubes are 12.5 feet long and 5.5 inches diameter. They are made from 6061 aluminum with 1/4" thick walls. Our local metal supplier didn't have too much trouble getting them.
- The sculpture uses 108 total ropes. Each rope passes through 3 holes total, so we end up with 108 holes per tube.
- The tricky part is to calculate the location of all the holes. The holes are spaced equally along the length of the tubes, but the angular locations need to be calculated using some non-trivial math.
- After calculating the exact angular position of every hole, we translated that into a machining jig. The machining jig was a semi-circle of wood that cradled the main tube. The semi-circle had angular marks on it showing the position of every hole and distance from the end of the tube. So, we positioned the jig and tube under a drill press and went down the length drilling all the holes at the proper angle.
- Then we deburred all the holes. Many of the holes have black press-fit plastic glands also, so the rope slides better.