I like to carve hands from pink insulating foam. You can buy it at the builders supply.
Cut it into chunks on the tablesaw, then use templates to mark the chunks and saw out the profiles with a coping saw. Fingers and details can then be carved using a combination of tools; I use a boxknife, coping saw, and various files.
Here are some hands stuck on nails for coating with epoxy.
When the shape is right I slice a slot in the wrist that fits a piece of 3mm (1/8") plywood -- a table saw will work or a radial arm saw is even better. A carbide blade makes a slot in the foam that exactly fits the thickness of the plywood. The plywood piece makes the arm up to the elbow and includes the tab for the control rod. Slide it into the slot in with some glue and lightly clamp.
The plywood makes the base of the hand very strong but the fingers are still vulnerable even if you coat them with epoxy... and there have been some broken fingers among the Rhinoceros players. One solution is to fiberglass the fingers. At the hobby store you can get very light .7oz glass fabric. Just cut little pieces and stick it on with more epoxy, front and back. Problem is solved. Here you can see the glass fabric and the plywood stiffener.