As with all of my straw projects, you can take pride in using freely available materials. Unlike other constructions toys, the fastening process is part of the building material. After finishing this project, snapping together expensive injected molded blocks will feel like cheating.
This is a great project for kids and parents or as a classroom project. The project will require a bit of patience and take a few hours to fully build and assemble. If not assisted by an adult, I would suggest a starting age of 10 years old since the force needed to use the paper punch is too much for younger kids.
Wooden Skewer (optional)
Permanent Marker (optional)
That's it. The elegance of this design is that it is basically free and the assembly is pretty simple. Yet, this design achieves fully mechanical hand that rebounds back to its original state when the tendons release their tension.
For this project, the goal was to build a fully functional hand using only straws. The diameter of a McDonalds straw is just about perfect. You can substitute straws from Chick-Fil-A clear straws. I prefer the McDonalds straws because they have a yellow and red band that run the length of the straw which makes cutting easier. The yellow and red bands act as a visual guide and results in straight cuts.
The magic of this project is that it uses no glue, welding, staples or securing other than by creative use of the source building material. Straws are incredible building materials. They come in a wide variety of dimensions but share inherent strength, flexibility, and availability attributes.
Step 1: Materials
Step 2: Tools
Step 3: Finger Digits (Phalanges)
All four straw fingers can be made identically. If you wish, you can make the knuckle locations in proportion to a real hand with various lengths. That simply adds more complexity to the build.
You will notice that each finger consists of seven paper punches. You will make four equally spaced paper punches at the bottom of each finger. These will later allow us to create a palm to hold the fingers together. The three punches you make above the palm are at 90 degrees to the palm punches. These are the knuckles and you can hold a straw up to your hand to determine the best location for these punches.
The knuckles require a bit more work to function. You need to remove half of the straw below the hold punch. You can either use scissors to make a nice V shape or just double punch offset below the first. After a lot of experimenting, I think the V shape is both faster and gives a superior 'bounce' for returning the finger to its resting position. Play around with the knuckles by flexing the finger to check for a nice easy bend. Look for plastic crimping and remove that material. The finger should snap back to a straight line when released. If not, you removed too much material.
We will build the opposable thumb as separate series of steps later in this guide.
Step 4: Tendons and Fingernails
Step 5: Finger and Tendon Assembly
At this point the fingers and tendons are almost complete. Before you can join these two pieces together, you need to make two more cuts per finger.
First, cut the top of the finger along the same parallel line as the knuckle joints. Only go down about a 1/8 of an inch to 1/4 of an inch. You don't want to cut to the first knuckle, as that would destroy the finger. This cut is what will anchor the finger nail.
Second, cut a section off the bottom of the finger so that the final ring pull can be grabbed.
Thread the tendon by pushing the fingernail up from the bottom of the finger. It will slide up the tube easily and shouldn't pose a problem. Anchor the fingernail at the top of the finger. Grab the ring pull and gently pull it while hold the finger. With just the right amount of tension, the tendon will force the knuckle joints to collapse and the finger will bend.
Use this time to remove addition material as necessary to allow the knuckle joint to operate properly.
I find it best to 'break in' the knuckle joint by manually flexing them a few times using my hands instead of the ring pull.
Step 6: Palm
The palm starts off easy enough but the addition of an opposable thumb will truly test your patience. Take your time.
Begin by cutting four shorter straws to act as a matrix for the fingers. The picture below shows a suggested length of approximately 1/3 the full length of a straw.
Step 7: Thumb Supports
While we used four straws for the palm, we will only need three for the thumb. More than three will prevent the thumb opposable movement. We will be striking a balance of strength and flexibility.
For the each of the three straws, punch four holes in the exact same location as the palm holes. Very carefully cut the straw in half between the holes and stop about 1/4 inch past the last hole.
Insert one palm straw into each thumb support. Align the holes.
Step 8: Thumb
Step 9: Hand Assembly
The first picture shows that the thumb supports are arranged with one at the top of the hand and two at the bottom of the hand. The picture also shows that we have not yet cut the length or punched holes. This is intentional as the final cuts are not known until the first four digits are in place.
Also pictured is the optional wooden skewer. This can be used to push inside the finger and return the straw back to its normal tube shape if the crimping was excessive. Don't worry about having it look perfect. All that is important is the free movement of the tendon inside the tube of the palm. If it can move freely and the fingers are roughly aligned by the fingernail, you have assembled it correctly.
Having threaded the four fingers through the palm, place the free floating thumb assembly on top of the extending thumb supports at an angle roughly approximate to your own hand. You know have a rough guide as to where to punch the holes for threading the thumb.
Step 10: More Thumb Work
In order for the thumb to be opposable, you will need to allow the thumb to collapse into the palm. Flip the hand over and punch holes for access between the thumb and finger. Cut a generous amount of material out of these locations.
Check your work by making sure the thumb can collapse and fold into the palm. The picture shows the free movement of the thumb by 90 degrees. Nice.
Step 11: Optional Thumb Tendon Relocation
Step 12: Have Fun and Next Steps
Future projects we will be posting include straw gears, straw pendulums, straw springs, straw water bell siphons, and straw bridges. Straws are great. They are an easy builder entry point for kids and the cost makes it nearly irresistible.