I was discussing the 22" Cassegrain configuration with Jim and he said that he had a 7" piece of glass that would be perfect for the secondary. He brought out a 7" piece of crown that was left over from building his 7" f15 refractor. The crown was strained and returned to the manufacturer, Hayward Glass Company. They sent him a new blank which he used for his 7" refractor. Hayward Glass annealed and returned the other 7" crown element. (What a great company. I wish they were still around!). He thought that It would be a good deal for the secondary since I could test the convex surface through the back of the lens. Jim gave me the crown element. I decided to make a refractor in Jim's memory and use pyrex for my 22" Cass. focus. I purchased a flint element much later. My friend Bob used OSLO to calculate the optical configuration for an f12 refractor. The optics are shown in Figure 1.

Figure 1. The flint is in the back row left. The surface with a 220 grit ground surface. The finished crown element is to the right The plaster/tile tool is at the bottom left and a home made sphereometer is to the right.

The flint element was purchased with the curves generated. I was fortunate enough to have a Professional Optician assist in  fabricating the first surface of the flint element. Having a master optician assist in making the surface was very interesting. Many of the techniques I thought were necessary were not. I found that pitch laps do not have to be neat. Hand cut channels are fine.

It was left to me to finish the last surface. Unfortunately, I had to postpone working on the lens for a very long time. After more than 12 years of neglect I finished the first round of grinding on the last surface about 3 years ago. I needed to go through the rest of the grades of grinding.

I started working on the F4 lens again, Jan, 5, 2005, I went through the remaining grits very fast. Flint is a really soft glass and work incredibly fast. After a few hours I finished with 12.5 micron and was ready to begin polishing. I made a pitch lap with burgundy pitch. Figure 2.

    Figure 2 Grinding table pitch lap and flint lens. Notice the pitch lap squares are hand cut. Precision is not required.

The F4 flint lens doesn't like thermal shock. My normal method of making a pitch lap, where I pour the pitch on the curved surface of the mirror could not be done. The lap was still easily done by doing a normal pour of pitch on the tool with a dam. A second pour was made on top of the still warm pitch. I let the pitch cool enough not to break the lens but remain soft.  The lens was covered with waxed paper and the lap was pressed onto the lens to conform to the len's curve.  When the  pitch was completely cool channels were cut by hand with a single edge razor. This technique was almost as fast as my normal method taking around 1 hour including melting the pitch.

The grinding table is simply a piece of 2" x 12" pressure treated wood with a Formica surface. Three wooden cleats hold the tool or lens in place. Instead of "walking around the barrel" I simply change the direction of stroke as if I were walking around a barrel. Alternately I could turn the tool or lens every few strokes. I learned this trick form the Telescope Makers Workshop. Doing things this way allows me to grind in the warmth of the house instead of the garage.

Refractor Mount

    Figure 3, Dec Shaft and counter weight.

The Dec shaft extension came from some machine that was scrapped out some time back and it was 1.25" which, was perfect for the counter weight that I had left over from the Cave Astrola. I made the Dec assembly for my 6" cassegrain mount, so I could convert the fork mount to a german mount. I rarely used this configuration.

Many years ago when I first started making telescope I was given the base for some type of rotating device. (A radar mast perhaps?.) After many years of carrying it around I pressed the stainless steel shaft form the housing. The shaft is about 4" in diameter and had bearings and a rotating assembly on the 4" shaft, Figure 4. I decided to make an adapter to mount the Dec shaft on the end of this assembly. The Rotor for this suspected radar device was fixed and the formally fixed shaft be came the polar axle of the new mount.

FIgure 4 The RA shaft showing the worm gear and clutch.

I had two identical worm gears about 8" in diameter. I have made clutch mechanisms for both gears and mounted them on each axis. The saddle is a surplus casting from another telescope mount. The basic mount is done. I need to adapt it to a tripod and add a drive. I have know idea what the tripod looks like, (Somewhere in my garage are the parts to build tripod I just haven't found them).

Figure 5 another view of the mount.

The clutch mechanism for the Dec axis is made so the saddle walks around the gear, as opposed to having the gear drive the shaft.

I have a Meade AutoStar controller form a smaller refractor I bought about a year ago for parts that I plan to use as a drive. I'll post more as I get more done.