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Building an 8" Closed Tube Reflector

Construction Pictures
Finishing End Cap and Cell

NOTE: Resin and acetone should only be used in an open and well ventilated area and not where there are children. Read the instructions on the resin and acetone containers and use good sense and take precautions in their use.

For finishing wood parts and general gluing of the parts I use polyester resin. It dries fairly quickly. Ace Hardware can get it for you by the gallon or quart. They used to stock Evercoat resin but now they carry Bondo resin. They appear to be very similar products. Two quarts ought to be enough. Get some extra resin hardener, perhaps two of the larger 1.35 fluid ounce tubes. I use about three to four times as much hardener as suggested. You will use acetone to clean things up. Acetone is a flammable liquid and gives off potentially harmful fumes in a small poorly ventilated area. Do not use around an open flame and allow no smoking in the area you are working. Small and unsupervised children should not be in the area when you work with resins and acetone. You will possibly have these liquids in wax coated paper cups and similar containers and they can be mistaken for soft drinks. - Be careful.

Working with polyester boat resin is not quite the same as painting. Don't wipe your eyes with your resin coated hands - it burns. It will ruin any clothes you wear. This stuff acts as much like a glue as a protective coating, one of its main advantages and one which I have exploited in my design. The resultant structure is immensely strong as well as light for its strength. It also has a short working life and can be a bit nasty to clean up. All cleanup is done with acetone. I use about three or four times as much hardener as recommended. This speeds up drying but shortens the working life. Plan on using a batch for no more than 5 or 10 minutes. When it starts to gell up, stop at once and clean the brush in a container of acetone. It should dry enough to handle in about three hours in a warm and dry environment. On humid days and in colder temperatures it will take longer. All parts should be laid out on ordinary wax paper. It will not stick to wax paper but will stick to about anything else and it will have an extreme reaction with and destroy Styrofoam. Use cheap brushes of 1" to 1.5" width. Application should be on flat level surfaces. Paint one inside and one outside surface. Let dry and turn over and do another two surfaces. You'll try to be neat but things will get a bit messy. Just have plenty of acetone ready to clean up things.

Once the tip-tilt plate and end cap is cut out and holes drilled they can be coated with polyester resin. Note tip-tilt plate collimation holes. Holes have been enlarged about 1/3 of the way through to receive and hold the nuts. Also, note the recessed center hole. This allows nut to site below the surface of the tip-tilt plate and not interfere with the fan assembly.

Once sanded they can be assembled as shown. Note inserts (see below) at right (inside and opposite of collimation screws) to receive fan mounting screws.

Inserts: Wood inserts are metal combination screws and nuts that are threaded to take a machine bolt of the desired size, in this case a 10-32, but are also threaded on the outside so they can be screwed into wood. The inserts need to be threaded into a hole pre-drilled with a .275 drill. The end of the insert takes an Allen head wrench as shown below right.

Collimation nuts can be held in place with silicone RTV. It's flexible and holds well enough.

Cyanoacrylate (super) glue can be applied to screw holes and inserts after they have been screwed in place. It turns the MDF and plywood into a hard material you can almost tap for threads. It should be sanded afterward and will make a nice smooth finish. Cyanoacrylate glue can be purchased in serious quantities from some hobby shops or over the Internet in various viscosities. The thin stuff is what I use here to soak into the wood.

Final assembly of the combination end cap, cell and fan can be seen here. Note 2.1 mm power jack in picture to left. The fan is mounted by super gluing a piece of soft rubber or sponge at each corner of the fan and then gluing the fan to the mounting plate as shown.

Close up showing fan mounting plate and 2.1 mm coaxial power jack.

Final assembly of the end cap mounted on tube and ready to be painted.