Constructing a Half-Moon Aquarium

By Bob Huntington

Many people have wanted instructions on making those little PVC & acrylic field aquariums so popular at UTMSI and Galveston Island State Park. There are two sizes, 6” and 8”.  6” are better for the wee ones. These are minimal instructions with no illustrations. (Photos are on page 2).

You are needy EDUCATORS!  Smooze, wheedle, use guilt, beg for scraps, donations or at least discounts from suppliers. Especially for the pipe – you likely don’t need a 20 ft. piece of 8” pipe! Explain what you are doing – who knows what might happen!  Go in as a group on a full sheet of acrylic and full piece of pipe and have a fabrication party! 

SAFETY is # 1!  Because plastics are tough and precise, smooth cuts are needed for good glue joints, power tools are the way to go. If you don’t have them or the experience to use them, con (or pay) someone into making these cuts for you. Feed work slowly and let the blade do the work.  The gluing should be done in a well-ventilated area or outside. If you are only making a few, you shouldn’t need a solvent breathing mask. If desired, solvent-resistant gloves are available at home centers.

Materials: Schedule 40 (white) PVC pipe from a plumbing supply house, 8” ID or 6” depending on the size aquarium you want.  Acrylic sheet, ¼” thick, from a plastics supply house or in smaller amounts from a home center. Slow-set, heavy-bodied PVC cement. Optional: ¼” nylon rope and ½” PVC pipe. (Ask your local glass company, such as Binswanger if they can give or sell you scraps from their jobs. The Plexiglas must be at least 8” or 9’ wide.)

Cuts: Acrylic – Leave paper or film on both sides.  Use a carbide blade, at least 60 tooth, preferably 80+, on a 10” table saw.  Cut rectangles of 5” x 7” for the 6” aquaria, 6.25” x 9.25” for the 8”.  Don’t forget the kerf, or waste that the blade cuts out – make a short cut into a scrap piece of wood to measure the kerf.

PVC – 2” wide rings in 8” or 6” pipe.  This is tricky because the rings have to be perfect.  Ideally, the best cuts would be on a huge radial arm saw (like they have at wholesale pipe suppliers) or a large band saw. Most folks don’t have those available, so here’s an improvisation.  This method requires a perfect end starting cut as a guide, so you might explain this to them at the supply house and ask them to cut it for you.  Most supply houses will give you 1 or 2 free cuts on a 10’ or 20’ length. Another way is to tightly wrap a sheet of poster board around the pipe, aligning both ends and tape it in place.  Draw a line along the edge of the poster board and carefully use a jigsaw to cut along that line and use coarse sandpaper or a bastard file to flatten and tidy up the cut.

Make a stop fence out of two pieces of ¾” plywood, 6” x 36” and a 12” x 36” glued and nailed at 90° along their long sides. Set the saw rip fence to give a 2” cut. Clamp the stop fence across the back of the saw with the 6” piece up and exactly perpendicular to the blade - if the angle is not exactly 90 degrees, you will cut spirals, not rings.  The stop fence should be set so that the center of the pipe will be sitting over the center of the blade while butted up against the rip fence. (CAUTION! If you are not experienced with table saws, DO NOT attempt to do this your self.)

Retract the blade below the table surface, place the pipe up against the stop fence and its end against the rip fence. Start the saw and slowly raise the blade into the pipe until ¼” of blade shows above the cut inside the pipe – minimal blade exposure is safest. Carefully and slowly rotate the pipe toward you while holding it against both fences until you have cut off your ring.  Stop the saw or lower the blade below the tabletop before trying to move any pieces!

Both faces of the ring need to be sanded smooth against a flat surface. A stationary belt sanders or large disk sanders are ideal and a disk sander can be made with a plywood disk mounted on a bolt and set into a drill press. But, if only making a few of these, you can use spray adhesive to attach a couple of pieces of 120 grit sandpaper up onto a very flat surface, like an old piece of glass, sanded plywood, polished stone, formica or even your table saw top. Just be sure it is a surface you can sacrifice or safely remove the paper and glue from. Hold the ring down on the paper and move it around in circles and figure eights until you get an even surface on the ring edges.

Remove the paper from one side of each acrylic rectangle. Careful: remember that any cement that gets on the acrylic where you don’t want it will permanently mar it. Apply cement liberally to the edge of the ring that will be glued to the acrylic and carefully lay the exposed side of one rectangle onto the ring, centered from side to side and with the ring ¼” up from the bottom. Flip it over if you wish to check alignment.  Place something flat on the ring and a weight on that, leave for 30+ min.

Take another rectangle, apply cement to the other edge of the ring opposite the 1^st rectangle and while it is upright or tipped toward you to prevent getting cement on the other side. Aligning by eye, set the ring gently onto the other acrylic side. Adjust while cement is wet and unit is upright on a flat surface to be sure that it will be aligned with the other to stand upright properly. If you did a good job of making the stop fence, you can stand the aquarium in it and up against the vertical board to get it aligned.  Gently lay it down on the first side and apply a weight. Let it set up.

On a band saw or table saw and with paper still on, cut the projecting ring off flush with the top of the sides. The bottom corners can be rounded off on a band saw or sanded round. Gently sand down any sharp edges. 

The optional handle:  Cut 3 1/2 “ pieces of ½” PVC pipe. Drill ¼” holes, centered and ½” down from the top in both ends of the ring and ¼” in from the ends of the ½” pipe.  String a piece of the rope through the holes in the ½” piece, then in through the holes in the aquarium.  Adjust the length to your satisfaction then tightly knot the rope inside on both sides. Use a lighter to carefully melt or hot-glue the frayed ends and help  prevent the knots from coming undone.  Remove paper. Protect acrylic surfaces when transporting to minimize scratches. Enjoy!

Measure twice, cut once. Contact me by email if you have questions.

Bob Huntington zen.mantid@comcast.net      

Master Naturalist Mel Measeles has also constructed a number of these half-moon aquariums. measeles@swbell.net