Cheers JimCrafton! I just googled "Terminator Hand" and browsed what ever I could find,
:: Terminator Endo Arm :: has some good forearm shots but
Building a garagekit 1:1 Endoskeleton Arm - The Terminator Files Modelling FanProject actaully shows a physical endo arm model kit being constructed and is one of the most useful sites I came across (the one I relied on for the finger designs).
I've tried to keep it as close to the more detailed T2 arm as possible (look at collectable model webistes for this) and incorporate all the pistons and joints as they are shown in the films. However according to
Terminator, The (1984), Original Endo Arm, original / screen-used there are a few designs shown in T1+T2 (The original terminator arm in T1 and the updated severed version in T2 plus the T2 "good" terminator arm which all have different features). So although I didn't make any parts of the model up, it is a mish-mash of a couple of major designs.
As for the upper arm, I started off with a box and modified it with standard tools by addding cylinders where I needed and welded stuff together and then adding details last:
(I bought the 18" T-2 plastic model off ebay for about £30 so I had plenty of refs for the body itself; let me know if you'd like any pics of the area) and used cylinders for the pistons.
I haven't seen the grav tank tut so I'm not familar with profile curves, but I prefer modelling from primitves and ploys anyway- using the connect tool to divide the mesh and the turbosmooth modifier will help create curves and the chamfer edges tool will define sharp lines without them being too harsh.
Hope this helps