The Spider Has Legs

The Spider Has Legs

I finally got around to slicing this .050" steel into three spider legs, and attaching them to the diagonal holder.


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Obviously, I still have to paint everything flat black. Those are 8-32 screws holding the legs to the diagonal holder. It was very satisfying to drill the holes in the legs by measuring .500" from the bottom edge, drilling a hole, then measuring another 1.000" over, and drilled another hole. Because I had used precision tools to drill the holes in the diagonal holder, everything just screwed right in, with no obvious discrepancies in location. Since all three legs are identical, I taped them together, and drilled all of them at once.

Here you can see the one asymmetry.


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There are two set screws used for making fore/aft adjustments to the mirror position, at the top of the Delrin piece that holds the 1/4"-20 screw in position. The set screws are on opposite sides of the cylinder. I didn't plan quite far enough ahead, so I had to drill another hole in one of the spider legs to make sure that I could get access to both set screws.

If it looks like the legs in the picture immediately above aren't in the same plane, that's a perspective problem. They are actually within a few thousandths of an inch of the same position relative to that Delrin cylinder.

The .050" steel isn't stiff in the sense of extraordinarily rigid; that would mean something quite a bit thicker. Instead, better spider designs (as I fancy mine is) rely on tensioning the legs. Once I have the upper tube assembly (scheduled for January 18th delivery), I will bend the ends of the legs to a right angle, and bolt them to the inside of the tube. By having all three legs under similar tension, the diagonal holder will be in a very non-flexible position. Because the legs are 2" high, there's considerable resistance to rotation across the optical path, which is the most important direction.