I made a bit more progress today. The base plate now has the flanges attached:
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The mirror plate now has the "corral" pieces in place. These I made by rather the same method as the flange brackets, except that unlike the flange brackets which bolt to the top of the base plate, these are bolted to the underside of the mirror plate.
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Here you can see how the mirror clips attach to the corral brackets.
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Because this is only a 1.5" thick mirror, I was originally planning to make these mirror clips quite short--but then it occurred to me that if at some later time I wanted to use a higher quality 17.5" mirror--one that was a bit thicker--better to have enough room. The mirror clips are held in place by 1/4"-20 screws into the threaded hole in the corral brackets.
I made a tight enough fit that once the mirror is in the corral brackets, they are effectively a spring fit. Of course, if the telescope ever gets upside down, it would be a very good thing to have something more than a spring fit holding that mirror in place! So I will go ahead and complete the mirror clips.
I still need some more parts, which I expect to pick up tomorrow to put this all together. I need some 1/4" long 1/4"-20 bolts for the mirror clips (since they are holding two 1/8" thick pieces of aluminum together, and the extra length would run into the mirror), and some 1/2" long bolts to replace the existing 3/4" 1/4"-20 bolts that hold the flanges and corral brackets in place. It looks a little ugly to have the extra 1/4" of bolt sticking out, and it adds weight that I don't really want.
I need some 2" long 1/4"-20 bolts for the collimation adjustments. I already have the springs (which you can see in the picture above) that I salvaged from the existing monstrosity. Because of some compromises that I had made to keep using the existing tube and back door assembly, the current adjustment screws are 4" long--simply too big. I also need some of the furniture pads that I use to lift the mirror off of a direct glass to metal contact (especially of concern where they will be touching the bolts that hold the corral brackets in place).
The good news is that the total weight of the current mirror cell components is still only four pounds! I still have to add the 2" long collimation bolts, and the furniture pads, but I also get to knock perhaps an ounce or two off by replacing 12 of the 3/4" long bolts with 1/2" long bolts. I am quite confident that this will still be a 4 1/2 pound mirror cell--or about 1/4th the weight of the only commercial one this size that I could find. And I still have complete confidence in the stiffness of this cell! Materials cost so far is about $150--or about 40% of the cost of the commercial mirror cell for this size.
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