Saturday, April 25, 2009

Everything is coming together.

I bought the Sono tube that will become the body of the telescope, basically the tube. First I found one at Lowes but the ID (inside diameter) was almost exactly 8". I need an I.D. of at least 8-1/2" to be able to place the mirror cell inside the tube and still have enough space for the aligment (colamination) mechanism. I have a concept diagram below in one of my previous posts.

I decided not to purchase the sonotube from Lowes instead I went to Home Depot and took a look at what they had. Surprisingly they had different I.D. sonotubes. They had both 8" and 12" diameter tubes but then there were different ID 8" tubes. The reason for this is it takes up much less space if the tubes fit inside each other so there are 8" I.D. tubes and there are also 8-7/8" I.D. tubes and two or three other dimensions! The 8-7/8" I.D. tube is ideal.

The only problem with the sonotube is that it is not perfectly round. It tends to be inconsistant as is natural being a cardboard tube that does not need to be absolutely round. In order to make it round I will have to use the lower cell ring (see illusration below) as a shaper to ensure as close a roundness as is possible.

The mirror cell assembly will be made from 1/2" Baltic birch plywood a relatively inexpensive rather low quality plywood carried now by the 'big box stores', as they are known in woorworking circles. The reason for using Baltic birch is that it is a very soft and light, relatively sturdy and flat playwood.

I decided against oak plywood because of its hardness and weight. Although I may change my mind and re do the mirror cell in oak. You really can't beat oak plywood when it comes to stregnth. The ideal material would be aluminum and perhaps I will upgrade the mirror cell when I can find a machine shop that can fabricate the prototype, assuming it works of course.

The next step will be to determine the diameter of the lower cell ring and route it out.

Hope you keep reading.


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