A Dobsonian telescope mount is a two-part homemade non-equatorial telescope mount invented in the late '50s by astronomer John Dobson. Dobson was trying to create an inexpensive stable mount for large-size telescopes. His simple plywood pillar and box wraps a box mount with round ears around the scope, and sets it in a padded cradle atop the pillar. The "Dob" brought large-scale, home-built telescopes within range for thousands of backyard astronomers.
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Things you need
- Newtonian reflector telescope (10-inch outer diameter tube / 8-inch mirror)
- 4-by-8-foot sheet of half-inch plywood
- 2 yards felt
- Carriage bolt, 1/2 inch by 3 inches with washer and nut
- Two old vinyl phonograph records
- 1-inch screws
- Drill and bits
Cut two 10-inch squares and two 10-by-11-inch squares from the plywood sheet. Lay long sides over the ends of the short sides to create a hollow, topless, lidless box that is 10 inches square inside and 11 inches square outside. Predrill the edges, then screw and glue the box together. Test-fit the telescope. The tube should just fit inside the box.
Mark and cut two 6-inch-diameter plywood circles. Glue them to opposite sides of the box, and screw tight with 1-inch screws. Cut strips of half-inch-wide felt and glue them to the edges of the circles. Line the inside of the mounting box with felt so that the tube fits snugly in the mounting box.
Slide the scope into the mounting box. Balance the tube so that it balances when you hold the bottom of the ears (circles) with your fingers. The tube can be rotated in the box to adjust the position of the finder scope and focuser.
Cut two rectangular plywood sides that 12-by-26 inches. Cut a front-face piece at 13-by-18 inches. The front-face covers one side of the pillar. The fourth side remains open so the tube can be turned straight up.
Glue and screw the face to the 12-by-26 rectangles so that the bottom of the face is even with the bottom of the sides. Leave the back open. The sides are taller than the front.
Mark a 6-inch-diameter half circle on the top edge of the pillar sides to make a cradle for the ears of the mounting box. Cut the arcs out with your sabre saw, sand the cradle, and glue half-inch-wide felt strips to the inside of the cradle.
Cut out two 12-inch plywood circles and sand the edges. Bore bore out a recessed hole in the centre of one disk deep enough for the carriage bolt head. Use a 3/4-inch paddle bit. Glue one old phonograph record to the centre of the opposite side from the recess. Glue the other phonograph record to the bottom of the second 12-inch disk. Lay the disks together with the phonograph records between them. Drill a half-inch hole through the centre of both disks and the phonograph records, and bolt from the bottom up with the half-inch carriage bolt.
Glue and screw the pillar to the centre of the top stage of the disk assembly. Set the ears of the mounting box and scope in the cradles. The scope rotates and pivots up and down. It should cover the entire sky. Stain and varnish or pain the mount.
Tips and warnings
- After you collimate and align the scope, set it up in the daytime and focus on a distant object. Go away and come back in 15 or 20 minutes. Check again to see if the scope has moved. If it has sagged, increase the friction padding to prevent sagging, or tighten the bolt to reduce rotation.
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