Ball & Socket Cell Design

Originally, I constructed the cell as laid out in the book. I soon discovered that while turning the collimation bolts, one of the triangles on the wiffle tree would lift off the back of the mirror completely. Either the bar was riding on the flats and points of the nut or the face of the nut itself was not square to the threads. Adding washers between the nut and the bar relieved this condition somewhat but I was not satisfied. So I came up with a ball-and-socket connection to float the bars that hold the triangles in place.

Here is a picture of the components of one of the wiffle trees. I drilled and tapped a 5/8" teflon ball to accept the 5/16-24 collimation bolt. The ball is sandwiched between two 1" teflon washers that are screwed to the aluminum bar that the triangles are attached to. The top teflon washer (closest to the mirror) has a 1" stainless washer on top of it to prevent the ball from ripping through the thin (1/16") teflon washer under the weight of the mirror. The finished collimation bolt turns very smoothly, with the teflon ball riding on the teflon washer. There is NO binding on the other two trees when a collimation bolt is adjusted.

Click on pics for a larger view.

Double-Wire Sling

I went with the nylon-webbing for the mirror sling, as the book described. I soon found that the return bounce of the laser collimator would vary by up to 3/16" depending on the altitude that the scope was pointing. This was unacceptable.

I stumbled across some sites on the web that described different sling designs and wound up implementing the double-wire sling design. It turned out to be a great alternative to the nylon webbing. With the double-wire sling, there is no lateral movement of the mirror at all. Not only does this keep the optics collimated all night, but will be absloutely necessary if/when I get around to building that EQ table.

The sling is simple, attach two wires, (I used bicycle brake cable in black shrink tubing for the wires), one in each corner of the bottom of the mirror box. Take the wire that was attached to the lower left anchor point and attach it to the right sling bolt. The wire that was attached to the lower right anchor point will attach to the left sling bolt. The two wires criss-cross under the edge of the mirror. Adjusting the length of the wires will allow for centering of the primary mirror in the mirror box.