First we'll begin with cutting. Start with a large circle. A large trash can lid works good for a 20 incher which I'm building here. Not that size matters :) as this will work for any size chute. Draw your circle and cut it out or just cut it if you have a sharp knife.
Next, the markings for the eight shroud lines. I've seen some just fold it up and cut across the bottom. I avoid this. Balance is important as it will allow for a smaller chute. So first, fold in half and mark at the circle X's.
Next, fold the marks together at 12 o'clock like the black dots and mark at the circle X's
Next, fold the marks together at 10 and 2 o'clock like the black dots and mark at the circle X's
Next, fold the marks together at 10, 12 and 2 o'clock like the black dots and mark at the circle X's
This is the line layout of the 4 lines in the next steps.
This next image shows several steps.
1. Cut 3/8" wide strips of duct tape.
2. Fold tape onto the chute at the marks.
3. Punch a hole 3/8" from the edge.
4. Cut 4 lines (diameter * 2) + 8".
5. Melt the ends.
6. Mark 2" down from each end of the lines.
7. Fold the line ends down to the marks.
8. Heat the bend so the bend stays.
9. Feed each line through holes (above image).
10. Bend and whip the ends.
This next image shows the final steps.
1. Neatly grab each loop and place together.
2. Avoid all but one line twist (inevitable).
3. Put a rubber band near the end of the loops.
4. Rake the 1 line twist close to the rubber band.
5. Place another rubber band 2" up from end.
6. Whip just below the rubber band.
7. Remove rubber bands and add shock cord.
Learn to whip here