Saturday, January 2, 2010

Keepers and knobs added

After planing a piece of Brazilian Cherry left over from the construction of my dresser, I made two "keepers" to prevent the mirror box from sliding from side to side when the telescope is pointed near the horizon. After planing, I ripped a piece one and a half inches wide, then cut two pieces six inches long. I then bobbed the top corner and drilled two holes then countersunk them after reducing their width to 1 and 1/4-inches. Two holes 5/16ths of an inch were drilled all the way through for the 1/4-inch machine screws to pass through. On the rocker box, I made two pairs of blind 3/8-inch diameter holes to accept threaded inserts, which were installed with a bolt and nut after dabbing epoxy on them to keep them from coming back out. The keepers were varnished with three coats polyurethane and before finishing I notched out the sides of the tops facing the altitude bearings to prevent them and the keepers from scuffing each other.

The knobs for the pole blocks were ordered from Woodcrafters, a very good company for any woodworker to deal with. Among their numerous products are knobs with an internal threaded insert which are used to make jigs and other fixtures used to build furniture. I ordered eight of these knobs, one for each pole block. When tightened on the carriage bolt, they press the middle section of the pole block inwards, gripping the truss pole tightly without crushing them. However, the ends of the poles do not for some reason don't all lie in the same plane, the left hand poles are farther out than the right side poles by about three quarters of an inch at the ends. Since it is consistent on all four sides, I'm going to shave a small amount of wood off the left hand blocks to bring them in line with the right hand poles. The pole seats on the upper cage also need to be altered so the poles will slip into the seats. Apparently an angle of one or two degrees is all that's needed to rectify this problem.

I've also begun to order the components necessary to complete the telescope. I've already ordered the secondary mirror and a holder for it, and soon I will purchase a focuser and a finder telescope. I am planning to also install a Telrad. While I made the assumption the upper cage will be quite heavy for a 15-inch Dobsonian, I can add strips of steel to the tailgate if the telescopes turns out to be top-heavy.

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