Hobbies And Interests
Things You'll Need
Instructions
Mounting the Mirror
Cut a square out of plywood to fit your telescope tube. The tube must be two inches larger than the mirror. A six-inch mirror needs an eight-inch-diameter tube; a 10-inch mirror needs a 12-inch tube. The tailgate square should be the same width as the diameter of the tube. An eight-inch tube, therefore, gets an eight-by-eight-inch tailgate blank.
Draw two crossed diagonals across the square tailgate blank from corner to opposite corner. The "X" at the center marks the center of the square.
Set a drawing compass for the width of the radius of the inside of your tube--about four inches for an eight-inch tube and so forth. Set the point of the compass on the center of the tailgate blank and draw a circle. Use a sabre saw to trim the corners along the circular compass marks. Check to see that the tailgate fits inside the telescope tube. Sand the edges if you need to.
Draw a second circle with your compass that is an inch smaller than the diameter of the objective mirror. If the mirror is six inches, the radius of the mirror is three inches. Subtract an inch and set the legs of the compass at two inches. That will draw a four-inch circle (two inches less than six inches). This circle marks where the tailgate bolts will go.
Divide the second circle into six segments, marking six spots on the edge of the circle. Choose every other spot so that two of the three chosen face the cutoff corners of the tailgate. Drill 5/16-inch holes in the marks. Screw the 3/8-inch tailgate bolts all the way into the wood till the ends stick out a half-inch.
Cut a thin piece of cardboard into a triangle that covers the ends of all three bolts. Apply glue at the center only underneath the cardboard triangle. Position the triangle so that the corners of the triangle cover the ends of the bolts. Next, glue three one-inch squares of masonite on top of the cardboard directly over the bolts. Tack down the center of the cardboard triangle onto the glue underneath till it dries. The triangle protects the bottom of the mirror from the bolt ends. The bolts can then be used to adjust the angle of the mirror once you've mounted the mirror.
Cut four rectangular wooden blocks one-inch square at the ends and three inches long. Attach a disk-shaped rubber furniture stop to one end. These are available in the furniture hardware section of the hardware store. They look like a firm round rubber disk with a central hole for a screw. Screw the rubber stop into one of the long sides near one end. Measure the thickness of the mirror and leave enough room between the lower edge of the stopper and the lower edge of the wooden block. This is where the edge of the mirror will sit.
Attach the four blocks with small screws or epoxy glue. Space them evenly around the inside of the telescope tube at the bottom. The stopper should be on the high side of the block and facing inward to the inside of the tube at the base. Leave enough space below the blocks for the tailpiece to push the mirror firm up against the rubber stoppers and far enough inside the tube for the tailpiece to be screwed in place.
Slip the mirror inside the three wooden blocks and push the edges up firmly against the rubber stoppers. Slide the tailpiece into the lower end of the tube so that the cardboard triangle presses firmly up against the base of the mirror. The mirror should compress the rubber stoppers on the mounting blocks slightly. Screw the tailpiece into place with small screws through the tube into the edges of the tailpiece.
Adjust the aim of the mirror by gently loosening and tightening the three adjustment bolts to change the angle of the mirror in its seat. Make only quarter turns at a time. Be sure not to over-tighten the bolts and break the mirror. Over-tightening the adjustment bolts can warp the shape of the mirror. You want the bolt heads to press firmly but not be stiff.