Figure 4.1.1. The polar axis assembly prior to final machining. The polar axis consists of three components, a 26" disk, a light post base, and the south polar cap casting.
4.1 Evolution of the Mounting
The original design for an 18" telescope called for a mounting built in 3 or 4 pieces. Each piece needed to be light enough for one person to assemble in the field. A 22" would be a major challenge to accomplish similar portability. Even though the mirror diameter had increased from 18" to 22" we were going to continue to use the 10" channel for the base of the fork and fabricate the rest fork off of the channel. The 4" tubing would still be used for the polar axle and a 60mm piece of heavy wall tubing would be used for the Declination shaft. Aluminum plate was needed to fabricate the fork using the truck channel as the base. We stumbled across some 0.200" aluminum plate at the local scrap yard for fabricating the fork. At this point we felt that we had the major components for the fork and polar axis for a mount. We were going to do a fairly typical rectangular cross section fork fabricated of aluminum plate on the 10" channel. We would need to find a 4" I. D. polar axis bearing and some sort of base to mount the fork.
We were going to drive the telescope with a gear, but had no idea where we would find that suitable gear or if I could afford one. Bill used a 14" Byres Drive on his 12.5". We were at the Titan missile base near Chico when we found a 26" diameter 1.25" thick disk. It was a flange that was part of the LOX, (liquid oxygen), loading system for one of the Titan missiles. We decided that instead of using a 4" I.D. bearing we would use the flange as a polar disk and roll the disk on rollers. This arrangement would remove the requirements for the 4" bearing and a large drive gear, since we could drive the disk. We would continue to use the 4" tubing as the polar shaft. The fork would be built and bolted to the disk.
Bill and I were visiting the scrap yard in Orland. where we found a conical shaped aluminum casting. We immediately recognized this piece as a great polar axis. When we found the conical polar axis mentioned below, we abandoned the concept of a portable telescope in favor of a transportable telescope. The telescope would no longer be constrained by what could be assembled in the field but by what could be moved by a trailer. Not going for a portable telescope would make many options for a telescope mount possible.
The new polar axle shaped the final design of the telescope, in that the fork would be redesigned to match the dimensions of the polar axis. The cone's dimensions were 9" in diameter at the small end and 18" in diameter at the large end and was 18" long. The cone had an 8.5" hole in the small end so an adapter would have to be made for a south bearing axle. It is our conjecture that the casting was a light post base. A plug was cast in the CSU foundry and later machined for a 2.5" pillow block bearing. When the cone was mated to the disk, the assembly was structurally very sound and aesthetically pleasing, Figure 4.1.1.
Figure 4.1.1. The polar axis assembly prior to final machining. The polar axis consists of three components, a 26" disk, a light post base, and the south polar cap casting.