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The "Deep Space Scope" Design

Home | Astronomy | DS-3 | Rocker box construction

Ground board and bottom of rocker box, and top of rocker box, and rocker box after the addition of stiffening plates.

We will build the ground board and rocker box from the bottom up.

• Create the base of the rocker box. This is a square piece of plywood 15 1/2" X 17 1/2". Mark a center point on this board. Drill a 1/4" size hole in the center for a nylon screw. Using a drill, cut a 3/4" diameter countersinking hole about 1/3rd of the way through this board. Cover the bottom of this board with Formica, glued on with rubber cement.
• Create the ground board. Create a triangle 7 3/4" from the tip to the center, and about 11" on a side. Drill a 1/4" diameter hole in the center for a nylon screw. Create a countersunk hole here just like you did on the rocker base above. This forms the TOP of the ground board. Cut out three 1" diameter plywood rings, and glue and screw them to the edges of the triangle. Trim the triangle to match the contour of the 1" diameter rings. Place a 1/4" diameter, 1 1/2" length nylon screw through the ground board, and place a nut on it. This locks it into place. Then, on the opposite sides of the 1" diameter wood rings, place three 1" magic sliders at the outside corners of the baseboard triangle. These are the plastic things that people put on the bottom of chairs so that they do not scratch the floor.
  
• Cut two 4" X 15 1/2" boards. We will glue these to the top of the baseboard in a moment.
• Find the radius from the bearing center to the edge of the mirror box. Measure from the center of gravity (the centerline of the telescope at the location of the tape above) to the BACK BOTTOM EDGE of the mirror box. This will be the part of the telescope that is on the bottom and the furthest from the center of the bearings and must clear the center bolt of the rocker box. This will also represent the height of the center of gravity above the center bolt of the rocker box, after we add in a fudge factor.
• Assemble the base board and rocker box to this point. The height of the bottom of the curve that we need to place in the side boards of the rocker box is calculated as follows: Take the radius calculated in the last bullet. Add in the height of the center nylon bolt. Cut this bolt off to make it as shallow as reasonably possible. Add in a fudge factor of 1/2" to 1". We will need this fudge factor if we were off when we calculated the center of gravity. Next, subtract the thickness of the Teflon bearings (about 1/4"). Subtract the radius of the bearings created above. Mark this height on the side pieces. Then, draw an arc on these side pieces using the radius of the main bearings, plus the thickness of the Teflon bearings. This is how we want to cut the sides.
• Cut this arc.
• Drill counter sink holes into the Teflon, and attach them with 4 screws. On my scope, the Teflon centers are 4 1/8" from the center of the rocker box.  Generally, the further apart these bearings are, the more stable the scope. You will also be adding more force onto the Teflon, thus increasing friction (generally, a good thing). The further apart the bearings, the higher the rocker box. This is irrelevant, until it gets taller than the primary mirror box when collapsed for travel.
• Now, mark from the edge of the Teflon bearings to the lower corner of the edge.  Cut off this waste triangle.
  
• Glue the rocker box sides onto the rocker box bottom.
• Cut two stiffening plates, 5 1/4" X 16 1/2".  Glue these to the bottom of the rocker box.  Trim with the sander.
  
• Cut 4 small sticks, 1" wide X 3" inches long. Bevel the top of these sticks with the sander.  Cover these with the fuzz from a strip of Velcro.  Screw these to the sides of the rocker box to hold the bearings into place. (Notice that I only used two in the center picture above. This was changed to 4, over the Teflon bearings, in the right picture.)