"Plughole" focuser

I've always found focusers a bit of a problem, expensive to buy and difficult to make because of the scarcity of 1-1/4" I.D. tubing. This little job is dead easy and costs only a few quid.

    Materials:

• Sink waste outlet (plughole).

• 15mm self-tapping screw.

• Reel of PTFE tape.

• Short piece of 1-1/4" O.D. tubing (this is easy to get).

• Fibreglass resin (available from Halfords).

    Tools:

• Junior hacksaw.

• Drill.

• Glasspaper.

• Stanley knife.

• Coping saw (with hacksaw blade).

    Construction:

        Separate the the flange and tube of the plughole and cut down the latter to just above the threads. The plastic parts may need trimming with the knife.

        Place the threaded tube on a piece of tin foil on a level surface and the piece of 1-1/4" O.D., coated with a thin film of grease, concentrically inside this. Now make up the fibreglass resin and pour into the space between the tubes. When this has set use the coping saw to cut the inner tube and remove it. Check the fit of an eyepiece and sand down slightly if required.

        For locking eyepieces in place: drill a small hole in the side of the threaded tube near the top. File off the point from a self-tapping screw and insert.

        Wrap the PTFE tape all the way around the threads, pulling it tight as you do so and then insert into the flange part and work all the way in. This removes any play and makes for a smooth firm action.

        All that remains now is to drill some holes in the edge of the flange part for attachment to the telescope tube. Just use screws on a tube with a flat side. For a cylindrical tube a bracket can be made from a small square of wood or metal with a length of dowel or tubing glued along two of the facing edges. This will will provide a flat attachment face for the focuser and the dowels will sit on a curved surface, and can be fixed with epoxy.