building a dobsonian telescope - inserting mounting blocks

There are three parts to the finished telescope:

• Telescope Tube
  - Making the spider
  - Eyepiece Holder
  - Making the Tailgate
• Rocker Box/Ground Board
• Tube Box
• Inserting Mounting Blocks
• Finding Focal Length of Mirror
• Positioning Eyepiece and Spider
• Using the Telescope

Inserting Mounting Blocks in the Telescope Tube

"Mounting" (.mov) Time (1:35)

The mounting blocks help hold the primary mirror in place. They keep the primary mirror from falling forward in the tube. The mirror sits on the two bottom mounting blocks and should just clear the top two mounting blocks. This allows the mirror to be adjusted when the telescope is in use. The directions suggest that the bottom two mounting blocks be one inch tall and the top two mounting blocks be three quarter inch tall. Because the tubes vary in diameter, you will need to measure your tube to make sure this works. If your tube is less than eight inches in diameter, you will need to reduce the size of the mounting blocks. If your tube is larger than eight inches in diameter, then you will need to increase the height of your mounting blocks. Each mounting block is four inches long.

Measure the thickness of the mirror and add three quarters of an inch for clearance. Mark the mounting block. You will screw in a rubber stopper on this line on the side the will face inside the telescope tube. Do this with all four mounting blocks. On the side opposite the rubber stopper drill a pilot hole for the mounting screw two inches from the end. Measure three inches from the back end of the tube and mark around the tube. Drill pilot holes for the mounting blocks. Use a washer with the screws when you screw in the mounting blocks. This prevents damage to the cardboard tube when you screw in the mounting blocks. The mounting blocks should be equidistant.

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