After Gareth's great walkthrough on making a servo operated polymorph finger I decided to make an entire hand. With the help of Gao, Claudia and my assistant Rose we made 4 fingers and a thumb.
Gao found that running a piece of brass rod through the finger made your holes line up and helped keep the finger straight.
I have since made the palm of the hand.
Since we want it to be able to pick up an LMR coffee mug I had to make the palm fold along two different axis's as you can see in the photo.This was done by running a soldering iron through the palm until it was 90% of the way through, then placing the palm in water and folding it along the line. The molten polymorph is squeezed out. When you open the palm again it is easy to dig out the excess polymorph.
The fold near the thumb was necessary for the thumb to oppose the fingers. Because of the fold at the base of the fingers I had to abandon Gareths mounting holes and just melt the fingers onto the palm. This was done using a gas torch (a cigarette lighter will do) to melt the surface of the palm and fingers where they needed to bond. Squeeze them together then hold in place while they cooled.
Looking at our goal I think I am going to have to build an entire arm....
With Gareth's X-ray photo for guidance I've decided to make a more human style wrist joint rather than the conventional robot style. This means I have to make polymorph ball joints.
Started with some polymorph balls and rod.
I then used the soldering iron to bore a hole in the balls. Because molten poly morph builds up around the holes I did this in two stages, placing the ball in cold water until it cooled and then using side cutters to cut off the unwanted polymorph between stages.
I then heated the tip of the rod with the gas torch before inserting it into the ball.
As the inside of the ball was also hot from the soldering iron you get a good bond effectivly making it into a single piece of polymorph.
I cooled the ball in water and cut most of the excess off with a sharp knife
A bit of delicate heating and smoothing with a wet finger gives me a fairly neat finish. I then cut the rod to length with side cutters and used the gas torch to melt the surface of the palm and the cut end of the rod before pressing them together.
Making ball sockets took some experimentation. After several attempts I found that the best way was to start off with a ball of warm polymorph about the same size as the ball joint.
Squash it slightly and then put it in cold water for a few seconds so it gets a skin that is cold enough not to stick to the ball. It will go slightly white. This is very important.
Press it gently around the ball. Work from the outer edge towards the center until almost 2/3rds of the ball is covered.
Once you have it evenly spread around the ball, run it under cold water until it hardens. Rotate the socket around the ball as it cools to ensure smooth movement. The end result should be a ball socket that fits firmly on the ball joint but moves smoothly and can be removed without too much force if required.
The thickness of the wall will determine how hard it is to remove or attach, as I do not want my hand to fall off when it picks up something heavy I found the wall needed to be 3-4mm thick.
Next I made wrist bones (ulna and radius). Solid polymorph would be to heavy so I rolled out a thin sheet and then tried to roll it up neatly. Easier said than done as it sticks to itself easily. My first attempt on the left didn't go very well. The second was better. These are reasonably stiff but still flex a bit.
I then heated the end of the bone and the outside of my ball socket and fused them together being carefull not to apply too much heat to the socket as I didn't want to damage the inside surface or warp it.