You're on your way to becoming the next Cashore Marionettes! 

Thanks for the link -- and the praise even if it isn't deserved LOL. All I've done is a little technical investigation, Cashore does art.

I just have to say again that this hand is a work of art and is beautifully constructed.

I'd really like to eliminate the finger tensioning mechanism for the finger. This would greatly unclutter the interior of the palm of the hand and simplify construction.

That have two new designs that rely on elasticity of the "ligament" to provide the tension to straighten the joint after it has been bent.  In this sense it functions much like the hand that stiqman  provided a link to early in this thread (my particular aesthetic requirements still prevent me from adopting this approach entirely).



The design on the left the uses a flat ligament and relies on the stiffness of the ligament to hold the joints straight when there is no tension on the control string.  On the right the ligament is bent and must be fixed to the joints under tension (while stretched a bit).  The bend assures that the force vectors in the stretched ligament will hold the joint closed when there is no tension on the control spring.

The first design would be the simplest to construct but I'm not sure I can find a material that has both the necessary stiffness and elasticity for that design.  Latex, neoprene and several other materials would do for the second.  Finding small quantities 1/32" thick seems to be the greatest hurdle here--I'd hate to buy a yard just to find out it didn't work. But fixing the ligament while stretched could also be a problem.

Anyway that's were things stand at present. 

I think that new design #1 is going to be your best bet. My suggestions for the ligament would be either plain old elastic or a spring metal. Elastic may not last as long as spring metal.  If you used some type of spring metal I think that it would have to run the entire length of the finger and allow for movement of each joint along the spring metal. I guess that would depend on how close you can get the metal to the inside of the finger joint.

Another thought would be to not embed the metal into the joint but use it as a hinge of sorts on the inner joint.  That I think would come into play with your second design more since the spring metal would have to be slightly bent although the spring metal would still be holding the finger open.

I keep running searches for spring metal.   Have a look at this Goggle Search.

Just in case that search returns different then what I got here are some of the sites I found intrigueing.
Penninsula Spring
How to Make Springs
Ocean Spring & Metal Manufacturing Limited

Thank you for the suggestion.  But, if I understand it, I do not think it would work.  If you take a 4 inch long piece of spring metal and, holding it at its ends, bend it to 90 degrees the stretching that occurs at the outside radius of the bend (and compression that occurs at the inside radius) is distributed over the entire length of the metal. But I want joints to be close to each. This means that the radius of curvature that is created in the ligament when the joint bends is very small and as a consequence there is a good deal of stretching distributed over a very small area.  I feel fairly certain that spring metal, because it is neither malleable nor elastic would fail or at least be so deformed that it could not rebound.  The same would hold true for plastics of low elasticity.

Amateur - I really like the idea of simplifying and cleaning up the finger design.  I've been thinking of and on all day what kind of material you would need to used to load your joints with that would be able to function as both a finge and a spring.  Honestly I can't think of anything that would give you the ease of finction you need and still provide consistent and full return.

Which means that your modification is going to have to be closer to your original design which in my opinion is a very well thought out design.

That being said, if you can find a spring/joint material that will work you will have improved the design.

PS - perhaps you can relocate the return spring to some place other than the palm.

Shawn I think I finally figured out what you meant in your second paragraph. (d'Oh!)  Here is a design based on my interpretation of what you were saying.  It uses two spring wires.  They are in red in the drawing.  The wires would have to be capable of making bends with 1/8" radii for dowels 3/8" in diameter.  That doesn't seem imposable.  I'll start checking out the spring references you supplied. 



Thanks again.

Amateur - Just trying to follow your design process.  In your last drawing will the red spring wires stretch or bend and then spring back straight..  From your drawing it looks like it would be the latter.  If that's the case will you need to leave the wire so that it can slide in the channel it runs through?  It would seam that it would need to because when the hand flexes the outside of the fingers will longer than when they are straight.

I had another thought.  Why not replace the ligament with a small barrel spring, similar to a spring from a pen.  The spring would then act as both the hinge and the return.  I don't think it would change the look of your fingers.  They only trick part would be figuring out how to insert and secure the spring in the joint.

Hope I'm not being a pest.  I was working are some similar mechanics a few weeks ago and your designs have really got my mind working.

Hope I'm not being a pest. 

Absolutely not.  I'm always glad to hear new ideas.  You have to understand that it can take a while for my creeky old brain to wrap around them LOL.

As to the springs, it is the latter case, they are simple wires and bend. And you are correct, one end would have to be free.

This finger would use a fabric "ligament."  I guess the proper puppet term is hinge and I will adopt that.  I am afraid that it will stretch a bit and allow the joints to rotate about their long axis. This is why my design here uses two wire springs which would help stablize the joint.  I fear that a round spring hinge would not provide the necessiary stability.  But I don't know that (because I haven't tired it).

  I am afraid that it will stretch a bit and allow the joints to rotate about their long axis.

Hadn't thought of that but I think you're right.  Stronger springs would not be the answer because it would be too difficult to opperate the hand.  Pehaps you cound make a combination spring and ligament joint but in such a small area this probably wouldn't be strong enough to be durable.

I guess its looking for a spring steal of the right guage, flexability and tension.