Saturday, May 11, 2013

More "What Was I Thinking?" Discoveries

Very typically, telescope mirror cells have little clips on the side that hold the mirror in place.  (Yes, there's some felt between the clip and the surface of the mirror.)   Here's a fairly gross example:

In my case, I discovered that the clips extended far below the plate on which the mirror sits, and actually were scratching the flat black paint on the first plate.  This had several bad effects:

1. Damaging the flat black paint, increasing ambient light (very slightly).

2. Adding unneeded weight to the cell.

3. Increasing the actual distance from the front surface of the mirror to the back of the cell (which is an issue, as I previously have mentioned).

4. Reduced the amount of adjustment that I can actually make to the mirror.  This has not been a problem, and in practice, the length of the springs between the two plates is considerably more adjustment room than I should need, unless I put the mirror cell into the tube in a way that wasn't square.

So I took the clips off, trimmed off the excess length with the bandsaw, then milled them precisely to length (even though they don't need to be) on the vertical mill, and repainted them flat black.  I doubt that I even saved an ounce, but every reduction in weight is a win, especially at the mirror end of the tube, where any extra weight means more bending of the tube, and the mirror end is where most of the component weight is located.

There are a lot of places where I could probably reduce weight a bit more; the only question is whether it makes sense to do so.  When I went to Home Depot earlier to buy 5/16"-18 bolts, nuts, and washers, I looked for aluminum versions -- which they did not have.  If I could find them in stock somewhere (especially black), it would make sense.  It probably doesn't make sense to pay $20 shipping to have a mail order operation do so, since this can't even a fraction of an ounce that I would save.

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