The Light Baffle
Another unique aspect of this design is the open space past the secondary as viewed through the focuser. The opportunity for contrast robbing stray light to enter the focuser must be addressed. I chose to tackle this issue with a light shield held in place with a support frame. In keeping with my low hassle – quick setup theme, I wanted a baffle support that would attach easily and store somewhere in the scope so I could reduce the chance of forgetting it, and, make for fewer trips when bringing the scope out.
I planned on using a flexible steel band as a support for the shield. I found the material at the local lumberyard, it was the steel banding they use to bundle units of lumber together. I asked if I could pick up some scrap laying around the yard, and they begged me to take all I wanted. When I began working with it, it soon became obvious that it lacked the stiffness necessary for this application. It tended to sag into the light path as the scope was oriented at lower altitudes. I entertained ideas of a more rigid support, but did not want to abandon my goals of internal storage and was struggling for ideas. Finally it occurred to me that a combination of rigid and flexible would accomplish my goals.
I made two supports from 1” x 1/8 th inch aluminum connected with a piece of the flexible banding. The rigid supports kept the baffle out of the light path, and the flexible banding meant I could straighten out the support and store it in one of the tubes for storage and transport.
Now for a simple and quick way to attach this assembly to the scope. I wanted something that would not require tools and would be easy to do in the dark. On yet another search of the local hardware stores for a solution, I found these low profile frame hangers that were perfect for the job.
All that remained was to fashion a shield out of an appropriate material to attach to the support with Velcro. Luck was on my side when I visited a local plastic component manufacturer who provided me a perfect solution. It is a thin flexible plastic sheeting that was flocked on one side. The perfect product for this purpose.
The Balance Point
With the "tube" assembly nearly completed, I could now determine the balance point. With all of the components in place, (or surrogates of a similar weight) I placed it flat on the bench and placed a broom stick perpendicular under the mirror box. By moving the mirror box back and forth I was able to determine where the balance point of the tube is. It is there that the center of the altitude bearings will be mounted.
The Altitude Bearings
This was an aspect of the project that I was not confident I could pull off. In fact, like the secondary holder, I was prepared to order a set of pre made bearings, but decided to save the money and try myself. My trepidation was due to my relative inexperience with Routers. I felt that to do the kind of job that I wanted to do, I needed to use a router for this and other aspects of this scope. I owned a router, but did not have a suitable circle cutting attachment for it, so that is where I started, making a simple rig to help me cut perfect circles........right.
I planned to make the bearings 14" in diameter, and 1" thick. I cut them from 1/2" Baltic Birch plywood and laminated two together to achieve the 1" thickness. I did have some trouble with the cut, and did end up with some mistakes to correct. Fortunately, the mistakes could be sanded out, and sand I did. Using a bench disc sander, I was able to produce a pretty good set of bearings, just under 14". I then took the completed disc and cut it in half on the table saw.
I then attached the Ebony Star Laminate to the bearings using 1 hour Epoxy and a generous application of blue masking tape. The laminate was a little too wide and long, and since I did not own a laminate trimming bit for my Router, I stopped by a local cabinet shop who were happy to trim them flush for me.
The Rocker Box
Understanding where the tube balanced, and the final size of the bearings, I could now determine the height of the rocker sides and begin work on the rocker. I found that in order for the mirror box to clear the bottom of the rocker, I needed sides that supported the bottom of the side bearings at 13.5". Using that as a starting point, I laid out the profile of the rocker sides on a piece of poster board with pencil, compass and ruler. This was a great help to me in having a clear idea of the cuts I needed to make and I recommend it.
One unique feature of this scope is the aperture on the side of the rocker to make the azimuth scale visible. I needed to cut a semi circle shaped opening both in the bottom of the rocker, and the one side. I used a compass and a protractor to produce the desired shapes. I cut the bottom board with the router, and the side opening on the band saw.
The rocker was assembled with glue, nails and clamps in the same fashion as the mirror box. The bottom was fitted with a sheet of Ebony Star Laminate, again attached with epoxy. I placed some furniture glides on the sides to keep the mirror box centered and protect it's finish from rubbing.
The Ground Board
For the ground board, I had some design features to accommodate. I wanted to implement a system of leveling feet on this scope. In order to accommodate the feet I had in mind, I needed to have some upward travel for the feet, so I needed a fairly thick ground board. I was at the lumber yard when I came across a product that was perfect for my needs. It was an 18" diameter 1.25" thick disc of edge glued pine. It was the perfect size for my 17.5" rocker and was thick enough for my plans. Add to that the bargain price of $6 and you have a winner.
The Leveling Feet
Using the manual ALT/AZ finder system that I planned for this scope, I wanted to have some capability for leveling the scope, the system just works better with a level scope. Again searching the hardware store for a solution, I came up with a system that uses a rather unusual device as an adjustable foot. It is known as a PVC bulkhead fitting, They are sold in the plumbing department. What attracted me to them was the wide adjustable ring, providing about 1.5" of vertical travel, and the wide "foot" making for a nice stable base. In use, the ground board rests on the ring, and simply turning the ring in either direction either raises or lowers the scope. Simple and effective.
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