Home >> Science & Nature >> Astronomy

How to Make a John Dobson Telescope

John Dobson̵7;s simple telescope design has provided an easy, inexpensive and effective telescope mount for large amateur telescopes for more than half a century. The Dob as its called by its admirers is made of plywood and phonograph records and some nuts and bolts. It allows you to spend your money on large mirrors and optics rather than on expensive legs to hold the thing up. We will assume you have a standard ten inch Newtonian reflector telescope and are ready to mount it. That̵7;s where John Dobson comes in.

Things You'll Need

Ten inch diameter Newtonian reflector telescope (12 inch outer diameter tube)
4 x 8 foot sheet of half inch plywood
Two unwanted phonograph records
Felt
Glue
Saw
Wrench
½ inch by 3 inch carriage bolt, washer and nut.

Instructions

The Dobsonian Mount
- 1
  Cut two 12-by -12 inch plywood squares and two 12-by-13 inch plywood squares. Glue and screw them together to form an open ended box with an inside diameter of 12-by-12 inches. Slide the scope into the box. It should fit snugly. Drill and screw a screw through the outside of each side of the box into the sides of the scope tube to hold the scope in place inside the box. Be sure the scope balances when you lift it by the box.
- 2
  Cut two 6 inch diameter circular ̶0;ears̶1; out plywood. Sand the edges smooth. Screw the flat disks to the center of opposite sides of the mounting box. Make sure the ears are at 90 degrees to the top side of the telescope tube (between the focuser and finder scope).
- 3
  Cut two 12 inch diameter circles out of plywood. Drill a half inch hole in the center of both. One is the lower stage. Drill a ¾ inch hole in the bottom and a third of the way through the center hole to provide a slight recess for the carriage bolt. Insert the bolt from the bottom sticking straight up.
- 4
  Drill half inch holes carefully through the center of both phonograph records. Glue the bottom of one record, slide it down over the carriage bolt and press against the lower stage. Allow to dry in place. Place the second record under the upper stage and glue in the center. When dry, slide the upper stage over the bolt and bolt into place firmly, but not too tight. The two records should rub against each other allowing the stages to rotate easily, but with some friction.
- 5
  Cut two 26 inch by 12 inch rectangles out of plywood. These are the sides of the pillar stand. Cut an 18 by 13 inch rectangle out for the front of the stand. Glue and screw the front piece between the sides so its bottom edge is even with the bottom edge of the taller sides and the sides stick up 8 inches above the front.
- 6
  Cut a 6 1/8 inch circle in the top edge of both sides of the pillar stand. Sand and glue a piece of felt to the inside edge of both circles.
- 7
  Glue and screw the base of the pillar stand to the center of the upper stage of the base. Don̵7;t put screws through the base or it may interfere with the stages ability to turn.
- 8
  Set the ears of the mounting box with the telescope into the curved cradles in the upper sides of the pillar stand. The telescope should slide up and down in the cradles and rotate at the base so that the entire sky can be covered in all directions.

Astronomy