Big Bertha Rebuild: Mirror Cell Almost Complete
Here you can see it from the side, showing the spring suspension that allows you to collimate the mirror quite precisely to the optical axis of the telescope. Remember that because the collimation screws are 20 threads per inch, one complete rotation of the wing nut moves that screw 50 thousandths of an inch. Applying a little trigonometry to the angle involved shows that you can actually get motions of the mirror's face below a thousandths of an inch, if you make very, very slight movements of the wing nut.
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Here's the back, where the wing nuts do the adjusting. There's only an inch or so of travel, but that's quite sufficient, as long as you aren't grossly mispositioning the mirror cell in the tube.
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What's left? It turns out that the 3/8" long screws for the mirror clips are just a little long. I need to buy some aluminum washers. If I could buy some 1/4" long aluminum screws this size, that would be even better, but there's no local supplier, and buying a box of 100 of them mail order seems a bit excessive. It isn't like the shorter length is going to shave even an ounce off the total weight.
I haven't put the furniture glides onto the mirror plate yet. The furniture glides provide both a metal/glass separation, and provide air flow to speed up mirror cooling. Until I paint or have it anodized, there's no point in putting them in place, since they stick to the surface with adhesive.
I am ready to verify the dimensions before I order the aluminum tubes in which this, and the diagonal assembly, will fit.