|
|
|
||||||||
A SEVENTEEN INCH DOBSONIAN
LOOK CLOSELY:
This 17.5 inch Dobsonian is built mostly according to the recent excellent book The Dobsonian Telescope by Kriege and Berry. But it has two unorthodox and experimental features. The most obvious is the style of the altitude bearings. Not so obvious is the use of "torsional friction clamps".
NOTICE THAT I AM SUPPORTING ALL THE WEIGHT OF THE TELELESCOPE, INCLUDING OPTICS, WITH JUST TWO OF THE STRUTS!!
CLAMPLESS CLAMPS?
The Seurrier Truss tubes are held in place by friction (as usual), but the friction is induced by the slight inward cant of the tube sockets ( note the slight angle in the top left photo above). When the secondary cage is inserted, the truss tubes are pushed outward in their simple sockets. The leverage is substantial because of the long moment arm and the hardwood sockets grip the tubes nicely, as demonstrated in the third picture where I am supporting the telescope (including all optics) with two of the truss tubes. The sockets were not terribly difficult to make. I set up an block angled at the (about 20 degree) tilt from the corner of mirror box to the center of the secondary cage. Then I added an additional slight tilt (about 5 degrees) inward when I drilled each hardwood block. I used a drill press, but I'll bet you could do as well without one. The colimation time is about the same as with any other system but this system reduces setup and take down time a lot. I don't know if the "clampless clamps" will work indefinitely or will wear out. Stay tuned to this web site to find out!!