Santa Clarita and Northern Los Angeles County Area
Butterfly and Moth Site
Night collecting sheet and frame
This tried and proven collecting method has been used for many years, and makes a great companion for the mercury vapor collecting light. A collecting sheet acts as a reflective surface to increase light dispersion, gives insects a place to cling to when they arrive, and provides a convenient place to see and capture them.
The goal of the project is to create a large, low-cost, reasonably strong and lightweight frame/sheet assembly, which can be broken-down into a compact bundle for easy transport and storage. You definitely won't be doing any chin-ups on this structure, but with proper setup and anchoring this rig should be able to withstand a light breeze, especially if set up parallel with the prevailing wind.
Note that when constructed as shown, the finished assembly will stand about 7 feet tall, which could present a challenge for shorter builders/users. Using the fully-assembled structure is not recommended in windy conditions - it's basically a large sail!
Fortunately, the sectional design allows the user to omit leg and cross-bar sections as needed to suit the user's comfort level and local conditions. The design can also be modified so that the cross-bar legs can be broken-down into more sections for smaller size and greater versatility.
Here is a material list:
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1 white lightweight king-sized bed sheet (thanks, Bill!)
50 feet (approx) of lightweight rope.
3 or more spring-type clamps.
40 feet (approx) of schedule 40, 3/4" o.d. PVC pipe.
10 feet (approx) of 1/2" o.d. PVC pipe.
2 (90 degree) elbow fittings for 3/4" pipe.
1 can of pipe PVC cement(see detail photo below)
A Plumber friend of mine tells me that the grey stuff is best. :-)
Tool list/equipment:
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Hacksaw, pipe cutter or powered saw to cut PVC
Propane torch or other heat source (...or kitchen stove? Be careful!)
Heavy leather gloves
Here are pictures of the sheet frame, shown assembled and broken-down.
Below you'll find the equipment list and construction/use notes:
For the bulk of the structure I used about 40 feet of [schedule 40] 3/4" O.D. PVC pipe, rated at 400 PSI (at 73 degrees). This particular pipe was made in USA by Apache. The manufacturer is probably not so important as are the ratings, since the stiffness, strength and I.D. are certainly related. The 3/4" sections are joined together with 1/2" O.D. PVC, which just happens to fit snugly inside the 3/4" pipe. When acquiring your PVC pipe, be sure to check that the 1/2" pipe you choose slips at least 4" into the 3/4" PVC with a LITTLE (but not much) resistance. We want the parts to slide together easily without falling apart or wiggling sloppily.
PVC is pretty cheap at Home Depot, Lowe's, Do-It Center, etc. - especially the really long/bulk pieces. If it won't fit in your car, take your hacksaw and tape measure with you and cut it up right there in the parking lot! It only took me about 20 minutes to hack-up all the parts for this project. I wanted a more-or-less uniform length for all the sections, but to efficiently use all the material onhand I had to be careful how I cut-up the PVC, and settle for a few odd lengths made form leftovers for the cross-bar sections. See below...
This picture shows all the parts, laid-out in their assembly positions; a sort of "exploded view" for reference, to better illustrate how many of which sections go where.
Cutting the sections and joiners:
For the legs, we need 12 sections of 3/4" PVC (3 sections for each leg x 4 legs). Each section is about 28.75" long, totaling 86.25" (roughly 7' per leg). You can tailor the length and number of these sections to suit your needs. I used leftover pieces of 3/4" PVC from the legs to make the cross-bar. This resulted in 4 weird lengths (12.5", 20.5", 34", 34") but it made efficient use of the material. If you can have plenty of 3/4" PVC onhand, you can use three 28.75" sections and one 14.75" section. Make whatever length sections you like so long as the total cross-bar length comes out to the width needed to support your sheet. (101" if using a king-size sheet).
The joiner pieces are cut from the 1/2" PVC and should be about 8" long to provide a strong coupling. Shorter pieces will allow more slop and not provide the strength needed. You'll need to cut 15, 8" pieces to make the structure as planned here.
Now that the sections and joiners are cut, lets assemble them...
Assembling the sections and joiners:
Each leg consists of 3 sections, two of which have joiners glued-in. This means we need 8 leg/joiner assemblies total. The remaining 4 sections without joiners can be considered done (easy, eh?). To make a section with joiner, apply pipe cement to the inside of one end of the leg section (as far inside as the applicator will reach), and also to about 3" of the outside of one end of the joiner. Thoroughly coat it. Then slip the joiner 4" into the leg section so that half of the joiner is in the pipe. Use a twisting motion during insertion to help spread the cement. The pipe cement actually dissolves the PVC plastic (active ingredient is M.E.K. - Methyl-Ethyl Ketone) and fuses the material together. It also has a grey filler material to help fill gaps.
The cross-bar sections are made the same way. Remember, only 3 of the 4 sections get a joiner. If you opted to make more or less sections, just leave one cross-bar section without a joiner. The same is true for each leg.
Here's the fun part... Making the V-fittings. This is what we're shooting for:
This fitting joins the two legs and cross-bar together at each side. Two will be needed. It would be nice if there was an off-the-shelf pipe fitting with the correct orientation, size, and angles. However, I couldn't find one (if YOU do, please e-mail me the details!) so, we have to make them. Here are the parts...
Basically, we're going to take two of the 8" long 1/2" dia PVC joiner pieces, heat-up about 3" of one end, smoosh them together and then jam them into the 3/4" PVC elbow as far as they will go. We'll let them cool and harden that way, then take them apart, apply pipe cement and re-assemble them to complete the fitting.
Fortunately, PVC gets soft and rubbery when heated. It has to be heated enough to be pliable without burning it too much. It's important to heat only about 3" of one end of the joiner pipes so the rest of the pipe stays cool and round. A propane torch worked well, although burning the PVC a bit was inevitable. It looks ugly, but doesn't seem to cause any problems. If you're embarrased you can always paint it later. :-) A kitchen stove will also work, but the smell is nasty and requires good ventilation. PVC will actually catch fire, but you can blow it out like a candle and continue heating it.
I set the torch on a shelf and rolled the two pieces in my hands to evenly heat the ends. Note the distance from the flame. It takes a few minutes for the heat to penetrate the thickness of the pipe and make it all soft. Be patient, and most important - KEEP IT MOVING! If it starts burning, blow out the flame, back away from the heat a bit, and continue heating. Test the softness by pressing the ends against another surface. When ready, the pipe should bend and return (more-or-less) to its original shape.
When hot and pliable, smoosh and jam the ends into the elbow, as shown. A thick leather glove really helps prevent burns. Before the pipe cools, set the leg angle by spreading the two joiners about 3 1/2" apart (or choose your own leg stance angle) at the bottom. I found a knob on my old BBQ that happened to provide the right spacing. Allow the fitting to cool completely, perhaps 20 minutes or more.
Here are some shots of the fitting at this point. Note that the leg joiners should be at a suitable angle, and 90 degrees to the cross-bar. If any of these angles are off substantially, your legs could stick out in all weird directions, making the frame unusable.
Now make the V-fitting permanent. Separate the pieces, noting how they came apart. This will help in re-assembly. Coat the inside of the elbow and ends of the joiners with a heavy coat of cement, and re-assemble them. This series of pictures shows the details and a lot of views...
Some more shots showing the second V-fitting, and making sure the angles match. Finally, the finished fittings. You can see that my first one (left) is much more burned than my second(right) as I learned.
Here are some shots of the final product. It's not terribly pretty but who cares as long as it brings in the bugs! The sheet is simply folded over the top of the cross-bar and clamped in three or more spots with basic spring-type clamps. "In-use" photos and tie-rope setup images are forth-coming. Note that for such a large contraption, it breaks down into a very small package. Based on my experience with other sheet rigs, use of a few rocks and other natural tie-points in the field will reduce the need for additional items such as tent stakes, weights, etc.
An obvious weak spot is the V-fitting joint, especially considering the leverage the long legs and cross-bar can exert. Care should be taken to load the structure only with its own weight during assembly, and only with the sheet when fully assembled. With care, the structure should last for a long time. :-)
Additional notes and afterthoughts...
There are many options for securing the sheet frame to the ground or other objects in the field. Below are some notes on the method I came up with. We need to provide tension between the two V-fittings (to hold the cross-bar in place) as well as between each V-fitting and the ground (or other tie point).
A couple of medium-sized screw-eyes and 50' piece of rope is used for the job. The rope is routed through the structure as shown. I included a small diagram in one photo to illustrate the pattern.
First, drill a hole in the side of each V-fitting as shown. Make sure that the drill size is smaller than the outside diameter of the screw-eye, but larger than the core diameter (the shank of the screw-eye that the threads attach to). If the hole is too small, the PVC could crack (unless you heat it first). Then thread the screw-eyes in as shown. When finished you should have something the fourth picture.
I used one cross-bar section and the V-fittings to create a mini-mock-up to illustrate the rope routing pattern... Just route the rope through the screw-eyes as shown, then drape the ends over each screw-eye, and finally tie the structure down. Notice that when routed this way, pulling on the rope ends actually squeezes the V-fittings towards each other, keeping the cross-bar sections and V-fittings from pulling apart.
Below are some shots of the sheet rig in "low profile" mode during field testing, January 24, 2005. One leg section was removed from each leg to help deal with the breezy conditions. It turned out to be very convenient to select the number of leg sections easily in the field.
As can be seen, rocks from around the collecting location were used to secure the rig and sheet. The rig held together well, but unfortunately the wind was very bad for the moths! After 20 minutes of no activity whatsoever, I packed the whole mess and moved down the hill to a more wind-sheltered area in the canyon under some oak trees. I had moths immediately. The whole teardown, move and re-setup took only about 30 minutes.
Have success or failure with this or a similar project? let me know!
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