is made of corrugated card. "Corrugated" refers to the wavy paper
sandwiched between two other flat pieces of paper, a design which gives the
cardboard lots of strength (considering it's paper). 
The pint size will not work. Avoid juice and specialty beverages (like Lactaid) because some of them have more plastic in them, which makes it hard to glue and paint.
Virtually every tan-colored packaging box you see everywhere
is made of corrugated card. "Corrugated" refers to the wavy paper
sandwiched between two other flat pieces of paper, a design which gives the
cardboard lots of strength (considering it's paper).
Avoid the stuff used for large appliances (refrigerators) and the cardboard used to contain very expensive items (computers). Instead, just use the common boxes you can get free in any grocery store.
I use nylon mason's line and cut it with a lighter or match so it doesn't unravel.
One of the pencils should be un-sharpened and full length (about 7 1/2" long).
The most challenging part of this project--and the key to making it work -- is the double pulley you will glue together. If you look straight at the edge, you will see two different sized pulleys (orange). They are shown here without string for clarity, but separate pieces of string will be wrapped around each and attached at one end. The way the string winds onto and off of the different sized wheels creates the peculiar behavior.
The big pulley walls (light blue) are cut from milk carton, because it is thin and strong. The small and medium pulleys (orange) are cut from corrugated cardboard, because--if you put two together--the wheel is wide enough. There are printable patterns for the sizes. You can refer back to this "exploded view" if you get mixed up while gluing all the circles together.
A wooden pencil will be the shaft. We'll use a sharpened pencil while making the pulley, then switch to a new one for the final version. One end of each string is securely attached to each of the wheels. Hot glue will hold it all together. If you make the pulley right, everything else will be pretty fast and easy.
It's a good idea to skim over the whole page before you start. If an instruction seems unclear, try reading ahead a few paragraphs and looking at the next few illustrations.
We will start by cutting out a box from the bottom of a milk carton. The box will be the body of the dragonfly. We need the top of the milk carton for cardboard for the pulley.
Measure 4" from the bottom of the carton at each corner and make a mark (pen seems to work best on milk carton). Connect the lines with a straight edge.
Before we cut out the box we will lay out and punch 4 holes --one in the middle of each side. We punch them out now because once the box is cut the cardboard is more likely to buckle. Finding the center of each side where the hole will go is easily located if you carefully draw lines using a straight edge corner to corner. Where they intersect is the center. Lay out all four sides like this.
Using the ball-point pen again, punch 4 holes, one in the center of each side. Make the hole the full diameter of the pen.
Using a sharp knife, razor knife or scissors, carefully cut out the cube (the bottom) from the top of the milk carton following the line 4" from the bottom. Set aside the box while we concentrate on the top of the milk carton.
Cut open the top on one of the corners, being careful not to cut much into
a side. When you flatten it out, notice that 
there
is a seam on the inside of the carton, although it might not be in the middle
as it is in the illustration. That depends on where you cut it. In the next
step, do not use the section of the milk carton with the seam.
Click here
and print out the page. Rough-cut out (bubble cut) the 3 big circle patterns.
Some browsers--especially
Netscape--change the scale and the size of the printed pattern. If the printout
says something like, "Scaled-60%" try another browser. Also, the printout
has a scale check. It says 2" line to line or 5 cm line to line. Make sure
it's accurate. Use "tape doughnuts" to tape the patterns to
3 sides of the milk carton so that no folds go through the circle. Do not use
the section of the milk carton that has the seam. Cut out the 3 big circles.
To punch the holes in the center of each circle, I put the circles on 4 layers of a towel or wash cloth. I use a ball-point pen to start the hole, but pick up the circle and finish it with a pencil because the circles should fit tightly onto the pencil (the pen might be a bit to big). To finish the hole with the pencil, I hold the circle as shown and twist the sharpened pencil further and further in (then through your fingers) until it goes all the way on. Because you have already started the hole, you know exactly where the pencil is coming through, so there is no chance of poking your fingers. Try not to bend the circles as you make the holes.
Tape the patterns for the other 4 circles (2 small, 2 medium) on the corrugated cardboard. Cut them and make the holes the same way. You should now have 7 circles with holes. Take off the patterns and tape.
Milk carton has plastic in it to make it waterproof. This can make it hard for the glue to stick (next step). Although I started making these dragonflies with no surface preparation and never had a problem with them come apart, I think it's a good idea to scuff up the milk carton discs with a piece of sandpaper. Two disks will be glued on one side, and one disc will be glued on both sides. Concentrate the scratching toward the middle of the disc where the glue will be.
Skewer a big, thin circle; then a small, corrugated circle onto a sharpened pencil. Squeeze a bead of hot glue (shown in red) all the way around the small circle and quickly press the two circles together.
There are two things to do after gluing each new circle on. First, if any really big gobs of glue squeeze out from between the disks, scrape them off with a piece of cardboard before they get hard. Second, give the disks a twist on the pencil in case they got glued to the pencil.
Next, loosely tie the end of one of the strings around the pencil. Then side on the other small, corrugated disk. Lay a bead of hot glue around one of the the small discs and quickly push it against the other small disk, sandwiching and gluing the string in between. Once again scrape off large gobs of glue and give the circles a twist to break any glue connection with the pencil. The string is longer than it appears in the illustration.
Before we glue any more discs on, we have to create a skin of hot glue on the edge of the small corrugated cardboard discs. Imagine dental floss sliding in between two teeth. If the string on this project slips in between the cardboard discs -- or in between the layers of paper that make up the corrugated cardboard discs--in a similar way, the mechanism won't work. So lay down hot glue on the edge of the cardboard and use the tip of the glue gun to push it into all the cracks. Try to keep the string out of the hot glue. When the job is done, you should have a thin glue wall all the way around the edges of the small cardboard disks.
Now slide
on a second big circle (from a milk carton) onto the growing assembly. Squeeze
hot glue onto the small disc and push together. Use a "Q-tip" or something
to scrape off big globs of glue. Twist the disks. You are half-way done with
the pulley system. Making the second half is similar to making the first half,
using the medium size corrugated circles this time.
Slip on one of the medium sized corrugated
disks. Apply hot glue and press it to the pulley assembly. Scrape off any big
globs of glue and twist the circles on the pencil.
Loosely tie on the end of the second string onto the pencil then slip on the other medium corrugated disk. Glue, scrape off extra, twist.
Just as you did with the small disks, apply a layer of glue to the edges of the corrugated medium circles. Use the tip of the glue gun to push the glue into cracks and holes.
Finally, to finish the double pulley, slide on the last big circle and glue it on. Check the inside of the pulley assembly for globs of glue that might interfere with the string winding and unwinding. Try to use the tip of the hot glue gun to smooth them out.
Put a new, unsharpened pencil through the double pulley so the pulley is right in the middle of it. Wrap some tape around the pencil on either side of the pulley so it doesn't slide around. Do not wrap string around the small pulley, but do wind the string glued to the medium wheel around the medium wheel (it doesn't matter which way you wind it) until only about a foot of string remains unwound.
Get the box (remember the cut-off milk carton cube?). It has a hole exactly in the middle of each side. The pencil will rotate in two of the holes, while the strings will go out the other two holes on the top and bottom.
After lots of experimentation I discovered that it's best if the pencils fit very loosely in their holes. So before you insert the pencil in place, enlarge the holes that the pencils will go in. The holes should be about 1 1/2 times as big as the pencil (3/8" or 1 centimeter for a typical pencil). I enlarge the hole with a "Sharpie" type magic marker.
To get the pulley in, push one end of the pencil through a hole and push the
pulley to the hole. To get the other end of the pencil in the opposite hole
you will have
to push out the opposite
wall of the milk carton a little.
The final thing to do before testing is to get the strings through the remaining holes. The easiest way I know to get the strings through is a paper clip that's been straightened except for a hook on one end. Stick it though from the outside and snag the string inside. It doesn't matter which string goes through which remaining hole.
Test the mechanism by having the string from the large pulley go down and the string from the small pulley go up. Pull the strings apart but don't try to force it if it get's stuck. If the strings get off their pulley and wrapped around the pencil, or if a string gets wrapped around the wrong pulley, you have to untangle. There are several ways to do this. It can be as easy as flipping everything upside down and letting it unwrap itself, but usually you have to take a more active role. Pull one of the strings to unwrap toward the tangle point. If it gets stuck, help it along by twisting the pencil while pulling the string. While you are pulling out the one string, make sure that the other string is winding up on the proper pulley. That works 99% of the time. Every once in a while I'll encounter a tangle so bad I have to pull out the pulley and rewind it.
Of course, you want to avoid having the strings jump off in the first place. Slowing down seems to avoid it for the most part, particularly as it's coming back down. If that doesn't work, tape the cube to a table (open face up) grab both strings and move them back and forth and watch the pulley. Try to see where the hang up is. Is a string wrapped around the wrong pulley (not the one it is attached to) or around the pencil? Is there some kind of rubbing that binds the pulley?
The wings, eyes and tail all add weight to the dragonfly, so it doesn't get
stuck in the up position. It seems that the wings also help keep a little tension
on the strings and help
keep them
from jumping their pulley.
Cut off the bottoms of two milk cartons. Open the top. Cut open the carton at the seam--the corner where there is a small overlap.
Click
here and print out the wing patterns. Some browsers--especially
Netscape--change the scale and the size of the printed pattern. If the printout
says something like, "Scaled-60%" try another browser. Also, the printout
has a scale check. It says 2" line to line or 5 cm line to line. Make sure
it's accurate. Print out twice or re-use the patterns. Bubble cut (rough
cut) the patterns and use tape donuts to fasten them onto the milk carton sides
so that the dashed lines line up with the folds in the milk carton. Cut out
the wings.The folds help keep the wing on straight.
Remove the patterns and tape. Tape pairs of cardboard together. The tape is
purple in the illustration. Put on lots of tape at the small end, because that
area will take a lot of stress when the pencil/shaft fits into it. Slide them
on and test the dragonfly with wings. If you go very fast, you'll find the wings
fly off. Eventually, when you're sure everything's right, you might want to
hot glue them on. If necessary you can also stiffen the wing with hot glue or
something inserted in to keep the wings from flopping to the side.
The tail is simply a side of a milk carton cut in half lengthwise and taped
on. Cut out a rectangle. On the small sides, measure 1" (24 mm) from two
corners and make a mark.
Connect the
marks with a marker and straight edge, and cut on the line. Tape or glue the
wide parts to the open end of the body (the cube). I tape so the slanted side
of each piece is on the bottom. This means that the print side of one will face
out, while the white non-print side of the other will face out. Finally tape
the ends together.
I cut the eyes from --what else?-- the side of a milk carton. I don't have a pattern for the eyes. Use your imagination.
If you want to paint, you will need to scuff up the milk carton first. I have used latex house paints, and I think other types would work, too.
MORE ABOUT MECHANICAL ADVANTAGE For
explanations, activities and cool links related to the dragonfly with mechanical
advantage click here or on the picture. |
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