Tuesday, September 22, 2009

Pole seats












After careful consideration, I chose a method to connect the truss-poles to the upper cage that will not result in the danger of parts dropping onto the mirror or being lost. I made four blocks from Brazilian Lyptus I had left over from the construction of my dresser. After the glue set, I made a jig that would hold them at the angle I calculated to be the best for the pole bores, which was 9 degrees.

After trial and error I got the jig perfectly positioned on the drill press and clamped it into place. A 1-inch Forstner bit was then used to bore all the way through the block, which was clamped to the jig. After the pole bores were drilled, I needed to drill the holes for the bolts that will hold them onto the lower ring of the secondary mirror cage. Using locating pins I marked the exact location of the holes on the blocks, then drilled a 1/4-inch hole with a Brad point bit.

Next, I made a simple jig to hold the pole seats stationary while I beveled the edges just like the pole blocks for the mirror box. Unlike the pole blocks, I routed one side on the back of the blocks to make sure the light baffle doesn't get in the way of them resting flush on the ring.

The next task I did making the pole seats was making two nine degree saw cuts in the front of the pole seat blocks after drilling a hole for a bolt and knob. A third cut will be made to split the seats into two parts tied together by a bolt and a knob. These pole seats will work like upside down buckets when the telescope is set up and taken down. When the knobs are tightened, the poles will be gripped tightly without crushing them. Any forces that try to pull the cage out of position will wedge them more tightly into place and prevent major damage to the telescope from occurring if the upper cage should separate from the truss poles. The final step would be to sand and varnish them with several coats of exterior Polyurethane to protect them from the harmful effects of moisture.

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