Sphere and Dome in Zones

The old pattern books give both, but their gore methods disagree with each other; on the chord construction for zones five of them agree. Daugherty adds that many sheet-metal workers “prefer to make them from zones, as the pieces are not so apt to warp, and the labor is less in raising the zones” (1922, p. 150), and Teschmacher writes “It is best to make them from zones” (1911, Vol. VI, p. 21).

Neubecker, Daugherty and Teschmacher cut the crown as a disc whose radius is the top chord; Kittredge uses the plan radius of the top joint, a little smaller. Both are shown, and you choose which goes in the drawing. A disc of the chord radius has the same area as the part of the sphere it covers (our own arithmetic), so it can be raised to the cap; Kittredge’s smaller disc fits the top joint flat but has less area than the cap — about 4 % less in the 1000 mm example — so reaching the curve means stretching it, and Kittredge says nothing about raising it.

More pieces mean shallower zones to raise — the tool shows how far each one lies inside the sphere — and more seams to join. It accepts 2 to 24, the crown included.

Either every piece in one file, left to right from the base zone up with the crown disc last, or one piece at a time — choose before downloading. Each zone is one closed outline on the CUT layer (two arcs and two radial lines); the crown is a circle. No text, no laps.

ICS (1901, §19) lets the worker choose the zone widths and draws each zone along a line parallel to the chord rather than on it. By our own arithmetic, in the 1000 mm, four-piece example its zones come out 1.26 mm wider, with pattern radii 2.6 to 24.8 mm longer and angles 0.7° to 2.7° smaller. Kittredge (1901, pp. 251–252) shifts the divisions half a step so the zone at the equator is a straight band. This tool follows the equal division with the joints at the base and the top.