Mathis Instruments Equatorial Mounts
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.
The German equatorial configuration consists of a conical declination assembly. This 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.
The equatorial fork configuration consists of a pair of tapered fork arms and a central hub. The thick-walled arms are castings made of 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.
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.
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.
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.
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)
- Use an 8, 10, or 12-inch pier or column - steel or aluminum
- 10-inch (minimum) square or round top surface plate,
- Drill a 6, 8, or 10-inch bolt circle at the compass positions northwest, southwest, southeast, and northeast.
MI-750 Mount (14.0 inch diameter base plate)
- Use a 10, 12, or 14-inch pier or column - steel or aluminum
- 12 inch (minimum) square or round top surface plate,
- Drill an 8, 10, or 12-inch bolt circle at the compass positions northwest, southwest, southeast, and northeast.
MI-1000 Mount (15 by 18 inch rectangular base plate)
- Use a 12-inch or larger pier or column - steel or aluminum
- 14-inch (minimum) square or round top surface plate,
- Drill a 12-inch or larger bolt circle at the compass positions northwest, southwest, southeast, and northeast.
The MI-500, MI-750, and MI-1000 mounts are supplied with the Servo II computer control from Sidereal Technology. Using high-quality DC servomotors, this microprocessor-controlled drive system provides smooth tracking to an accuracy of 0.08 arc seconds per step with full "Go To" capability. An external computer is not needed, since the hand paddle provides basic control of the telescope. The Servo II control is ASCOM capatible, so you can use with many popular astronomy programs to control your telescope. You can position the telescope, center an image and control the tracking rate, and then park the telescope at the end of the night. This Servo II control requires a 12-28 volt power supply with a minimum output of 5 amps.
Mathis Instruments Equatorial Mount Features
- Main components with a distinctive geometry that combines style, strength, and function.
- Large aluminum castings that provide the outer structure of the mount.
- Telescope axes machined from alloy aluminum bar-stock and black anodized for durability.
- Shielded ball bearings that are fitted into the machined castings and support the telescope axes.
- Large worm drive gear on each axis with matching worm in a precision bearing housing.
- Spur gears or belt drive on each axis that connect the motor shaft to the worm shaft..
- Computer controlled DC servo motors with mounting brackets.
- Cover plates that shield the drive gears and servo motors.
Mathis Instruments Product Number: MI-750EFM