Mechanical Hands

As with all of my straw projects, you can take pride in using freely available materials  this design achieves fully mechanical hand that rebounds back to its original state when the tendons release their tension.

Equipment:
25-30 Straws
Scissors
Paper Punch
Card
Permanent Marker (optional)

Method:

Think of the finger build as having two parts.  You will build four fingers and four tendons.  The fingers are a straw tube with cuts to allow joint movement and retain enough material to bounce back into shape.  The tendons consist of a finger nail, tendon, and pull ring.  
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.  

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 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. The finger should snap back to a straight line when released.  If not, you removed too much material.

The Tendon run the entire length of the finger.  Using a single straw, you will cut a fingernail, tendon, and ring pull.  This is all done using scissors.  Take your time.  This is where a McDonalds straw shows its advantage.  Use the yellow stripe to filet the length of the straw.  Now you have access to cut the remainder of the shape.  Use the red stripe as the perfect cutting guide.  As a bonus, the tendon looks nice in red.  Round the top of the finger nail into a rough spade shape. 

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.

Draw around your hand onto the piece of card, and carefully caut around it.

Cut the fingers out and leave the palm.

Attach each finger onto the palm. Pull the tendons from the bottom and you have a working hand- a mechanical hand.