Jack Schmidling Productions, Inc.
18016 Church Road ~ Marengo IL 60152
Phone:815 923 0031 ~ Fax:815 923 0032 ~ Email:firstname.lastname@example.org
|Telescopes||Astro Photos||JSP Homepage|
This view shows the equatorial head mounted on a heavy duty professional tripod with tilt head adjusted to the local latitude. As is usually the case, a mount is no better than the tripod it sits on and they are never good enough. There is no substitute for a permanent pier and this design is very easy to install on a pier.
The key to the stability of the mount lies in the fact that the polar axis for this design can be as large in diameter as desired without the concommitant need for it to be long and consequently very heavy and hard to handle. In this example, the actual length is only 1/4" for a bearing surface that is 4" in diameter.
This is a closeup of the two basic components that make up the equatorial head. The aluminum disk (which happens to be a 4.25" mirror grinding tool) has had one surface faced off to a depth of 1/4" leaving a shoulder of the same width and height. The Declination Head is made from 4" polyethelene bar stock and one surface has been faced to mate with the aluminum plate.
It actually could be made from 3.5" stock and simply faced off. The shoulder on this part serves little purpose as the shoulder on the aluminum base and the faces carry all the load.
The two parts are held together with a 1/4-20 screw and captive nut which also provide means for adjusting the gross friction between the two. All the load is carried by the large mating surfaces and not the screw. Field adjustment of the friction is with the knob and screw that passes through the Dec head and works against the aluminum. A piece of nylon at the end of the screw provides friction without scoring the aluminum.
The declination shaft passes through a hole bored through the Dec Head at right
angles to the polar axis. I intended to use bronze bushings but found the plastic
made a totally satisfactory bearing. Friction is controlled by another knob and
brass screw (not shown) that presses directly against the steel shaft.
The aluminum plate can be mounted to a tilted tripod in a number of ways or bolted to an adjustable wedge for mounting on a pier.
This design can be scaled up to just about any size and I see no reason not to expect good performance out of the plastic parts even in larger sizes.
Although I have not yet done so, both a worm gear and setting circle can be stacked using the same shoulder approach. I just aquired a worm/gear set but it is much too large for this particular mount so I am scaling it up and starting another based on a 7" worm gear made by Andy Saulietis (email@example.com). This is a plastic worm gear that looks great and for $65, I just have to give it a try.
To be continued................
[Return to top of page]