Major Features
|
Mechanical Components The MI family of telescope mounts include the following major features:
The aluminum castings in each mount are molded using accurate patterns and cores that produce parts of consistent quality. The various machined components are made on computer controlled machines as well as precision manual machine tools. In particular, the worm assemblies are hand crafted, where consistent accuracy of .0001 inches (2.5 microns) is needed. The telescope axes, flange plates, and hubs are all machined from alloy aluminum barstock. The declination countershaft is threaded stainless steel, and all fasteners are stainless steel. All motors and drive gears are enclosed in protected casings. No brackets or gear boxes protrude form the mount, and all electronic components are enclosed. The finished mount has a conservative, handsome look with the black anodized aluminum parts contrasting with the durable "blue-white" painted castings. The conical style of the mount features minimal hardware with only essential adjustment bolts visible. The final product is a precision platform for CCD imaging, conventional photography, and visual observation. |
|||||||||||
|
Polar Cone and Base Each mount features a polar cone fitted with a large upper bearing and a lower guide bearing. These pre-loaded bearings support the polar axis. The polar cone is bolted to the concave polar base; the contact between these parts is on an arc whose center is near the top face of the north bearing. As one slides the polar cone across the base, nearly full contact is maintained with the base and supporting pier. The center of mass of the polar assembly remains near the center line of the pier. The polar axis includes an integral slip clutch, which is machined into the polar axis near the top of the upper bearing. This clutch houses a precision bronze worm gear. For easy setup and for telescope balance, the clutch allows manual motion of the telescope. When controlled by computer, the clutch is locked. This clutch design also provides a margin of safety in the event the telescope strikes the pier or other fixed object. The polar worm gear is paired with a precision worm that runs in class 7 ball bearings. The spring loaded worm bearing assembly allows fine adjustment of the worm to worm gear tension to minimize backlash in the gear train. The worm assembly and servo motors are inside a protective casing . No motors or brackets protrude from the mount. With over 25 years of experience in manufacturing telescope gears, we produce worm gear drives that provide high precision tracking and exceptional pointing accuracy. Prior to shipment, the tracking accuracy of each mount is measured. This quantified report is provided to the customer to verify that the peak to peak error is less than 5 arc seconds. |
Polar Cone and Polar Base
 |
||||||||||
|
12-inch diameter bronze gear with stainless steel worm
|
|||||||||||
|
German Configuration The German equatorial configuration consists of a conical declination assembly. This #319 aluminum casting is machined on special mandrels that assure near perfect alignment of the opposing bearing surfaces. The bottom surface of the declination assembly is machined perpendicular to the right ascension axis to an accuracy of 1 arc minute or better. The declination assembly features a large upper bearing and a smaller guide bearing at the opposite ends of the assembly. These pre-loaded bearings support the declination axis and the declination drive gear. The worm gear is in slip clutch, allowing one to balance the tube assembly whenever auxiliary equipment is added to the telescope. A gear casing houses the drive gear, worm bearing housing, and DC servo motor. No motors or brackets protrude from the declination assembly. A threaded, stainless steel counter-weight shaft attaches to a hub at bottom of the declination assembly. The counter-weight shaft carries 40-120 pounds of counter-weights, depending on the telescope load. |
|||||||||||
|
MI German mount
 |
|||||||||||
|
The threaded declination counter-weight shaft is stainless
steel that detaches from the declination assembly.  |
|||||||||||
|
Equatorial Fork Configuration The equatorial fork configuration consists of a pair of tapered fork arms and a central hub. The thick-walled arms are castings made of #319 aluminum with a tapered box design. Each fork arm is machined on a computer controlled milling machine, assuring perpendicularity of the machined surfaces and uniformity in each set of fork arms. The declination axis of the assembled fork is perpendicular to the right ascension axis with an accuracy of 1 arc minute of angle or better. Since the arms are detachable from the fork hub, the fork arm separation can be machined to the customer's required dimensions. The fork arms are bolted to the fork central hub using stainless steel hardware. Mechanical contact on two surfaces assures alignment and rigidity of the fork arms. The central hub with the attached fork arms is bolted to the top face of the polar axis. A pair of pre-loaded bearings in each arm supports each flange plate. The telescope tube attaches to these plates. Interfacing a particular telescope tube to the fork requires customer-supplied dimensions, and in most case some custom machining will be required One fork arm (usually the east arm) includes the declination gear housing with a fine pitch worm gear, a worm bearing housing, and a DC servomotor. A slip clutch allows one to balance the tube assembly and make fine adjustment whenever auxiliary equipment is added to the telescope tube assembly. |
|||||||||||
|
MI-500 and MI-750 fork arms
 |
|||||||||||
|
Polar Cone on concave Polar Base
 |
|||||||||||
|
Polar Alignment Each MI equatorial mount has fine adjustments for azimuth and altitude for accurately aligning the polar axis to the celestial pole. Along the lower edge of the polar cone and base are three recessed setscrews for polar alignment. One stainless setscrew is located at the back surface of polar cone. Turning this socket setscrew slides the cone on the concave polar base increasing or decreasing the altitude of the mount. With this setscrew, one can adjust the altitude of the mount to the required latitude of the observatory. A pair of stainless steel setscrews on the east and west side of the polar base allows one to rotate the entire mount. With this pair of push-pull setscrews, one can adjust the azimuth of the mount as needed. Initial alignment is generally easy. The mount should be installed on the pier or column within a few degrees of true north (or south). Using the azimuth and altitude adjustments, one can get within a few arc minutes of the pole on the first night. For a permanently mounted mount, very precise polar alignment is an iterative process extending over several observing sessions. |
|||||||||||
|
MI-750G Mount with 16 inch Cassegrain
|
|||||||||||
|
Mount Capacity Telescope mounts are usually the most expensive part of a telescope system. For economy, it is common practice to put a large telescope on a modest size mount. Over the years we have seen a heavy 24-inch Newtonian telescope on a mount designed for a 10 to 12 inch instrument. In one extreme case, there was a visible bend in the declination axis from hundreds of pounds of counter-weights. We recommend that you conservatively estimate the mounting requirements for the tube assembly, and if possible, "over-mount" the telescope. In this way, you can comfortable add equipment without exceeding the mount capacity. We estimate the load capacity of each mount as approximately equal to the weight of the supporting polar cone and declination assembly. The MI mounts are not designed as portable equipment, so we do not minimize weight to achieve portability. While there are excellent mounts available that are quite portable, the load capacity of any mount increases when you increase the metal cross-sections and thickness of the supporting base. The cast components of the MI mounts are generally heavy. They are designed primarily for installation at a fixed location. The MI-500 can handle 100-200 pounds (45-90 Kg.), the MI-750 has a 200-300 pounds (90-180 Kg.) capacity, and the MI-1000 can handle optical tube assemblies weighing 300-500 pounds (140-230 Kg.). Fork configurations can carry 30-40% less than the equivalent German mount. In practice, each MI mount can actually handle a telescope weighing at least double the stated capacity. However, the mount flexure would be large, the clutches would be inclined to slip, the drive motors would be over-loaded, and the stability of the instrument would be compromised. This unfortunate practice is common in the mass produced Schmidt Cassegrain telescopes popular with budget-minded backyard astronomers. |
|||||||||||
|
MI-500G Mount with C11 and 5 inch refractor
on a 10.5 inch steel column  |
|||||||||||
|
Telescope Tube Interface The telescope optical system attaches to the top of the declination axis (German configuration) or to the flange plates of the fork arms (Fork configuration). In either case, the customer must provide the appropriate dimensions so we can drill and tap the required bolt pattern or machine the required adapters. Matching an existing bolt pattern is straightforward. We can attach most popular dovetail adapter plates and commercial telescope rings to our German mounts. For fork mounts, the arm separation must be machined for a specific tube assembly. In many cases custom brackets and adapters may be required. For common tube assemblies like the C14, we have available standard brackets. |
|||||||||||
|
Installation A mount is normally attached to a steel, aluminum, or cement pier. The pier can be fabricated, a thick-walled pipe, or other rigid material. Each mount includes a base plate to which the polar and declination assemblies (German or fork) are attached. The base plate has a bolt pattern drilled to match the bolt pattern in the customer's pier. While we can accommodate various pier configurations, as a guide we recommend the following: MI-500 Mount (10.5 inch diameter base plate)
MI-750 Mount (14.0 inch diameter base plate)
MI-1000 Mount (15 by 18 inch rectangular base plate)
|
|||||||||||
