How to Make a Dobsonian-Mounted Telescope
The Dobsonian telescope is the brainchild of John Dobson. In the late 1950s, Dobson introduced a cheap and sturdy plywood telescope mount for reflector telescopes to amateur astronomers. The Dobson mount is so inexpensive that amateur astronomers can afford to sink their money into larger aperture scopes rather than prohibitively expensive equatorial telescope mounts. The mount design below works for an 8-inch Newtonian reflector scope.
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Things You'll Need
- Saw
- 4-foot by 8-foot sheet of 1/2-inch plywood
- Screwdriver
- Screws
- Glue
- 8-inch diameter Newtonian reflector telescope (10-inch outer diameter tube)
- Felt
- Drill with 1/2-inch bit and 3/4-inch paddle bit
- Two old vinyl phonograph records
- Wrench
- 1/2-inch by 3-inch carriage bolt, washer and nut.
Instructions
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1
Saw a pair of 10-inch by 10-inch squares from your plywood sheet. Cut two more 10- by 11-inch squares. Screw the four squares together to make a bottomless and lidless box that measures 10 inches by 10 inches on the inside and 11 inches by 11 inches on the outside. The telescope should just slide into the box and fit snugly.
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2
Saw two 6-inch circles out of plywood and attach them to opposite sides of the box with glue and short screws. Don’t screw through the inside of the box. Glue a strip of felt around the edges of the circles.
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3
Slip the 8-inch diameter Newtonian reflector telescope into the mounting box. Balance the scope so that when you hold the mounting box by the disks on the side it balances horizontally. The top of the tube is between the finder scope and focuser and should be 90 degrees from the mounting disks. Screw a single screw through each side of the mounting box into the tube of the telescope to hold it in place. The screw should not stick out more than a 1/4 inch inside the tube.
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4
Saw three rectangles out of plywood: two 26-inch by 12-inch rectangles to act as the sides and one rectangle measuring 18 inches by 13 inches to serve as the front of the stand. The back of the stand remains open for the tube to fit into when pointing straight up.
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5
Assemble the three-sided rectangle pillar so the two long sides are opposite each other and the front is glued and screwed between them. The side opposite the front is open, and the sides measure taller than the front.
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6
Mark a 6-inch half circle on the side of the top edge of the two sides to act as a cradle for the mounting box. Cut out the half circle arc and glue strips of felt along the top edge of the arc-shaped cradle.
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7
Mark two 12-inch disks on the plywood and cut them out. Use a 3/4-inch paddle bit and drill a recess hole one-third of the way through the lower base disk. Drill a 1/2-inch hole in the center of both disks and through the center of both phonograph records.
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8
Glue one phonograph over the center of the upper stage disk and another on the underside of the lower stage so the holes match up. When dry, put the two sides with the record together and insert the carriage bolt up from the lower base through the upper base and bolt it in place firmly, but not so tight it binds. The base disks need to rotate.
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9
Glue the pillar to the center of the upper base disk with the cradle arcs at the top. Once secure, simply set the disks on the sides of the mounting box into the cradles. The telescope should go up and down and round and round smoothly, but should stop and stay firmly in place. The scope should be able to point at any place in the sky.
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Tips & Warnings
Once you have collimated the mirrors in the scope and lined up the spotting scope, check to see that the telescope stays put and doesn’t sag or drift when set on an object. Set the scope on a daylight target and then walk away for 15 minutes, then look again. If it’s moved, add some tension to the stage bolt if it rotates. Add a little more friction padding to the cradle if it sags or lifts.
References
Resources
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