The design is based on the Longworth Chuck, it's a great movement and normally used for Woodturning. The chuck's original designer sadly died after showing the design at a club meeting. The late Mr. Longworth of the Hunter Valley Woodturning Club, New South Wales, Australia should be given full credit in this chucks movement.
I added my take on the design by giving it more mass, taken away the need for wingnuts (making it safer) and generally done as much as possible to make it useful - The nice thing about this design is that it could be made in any material with very little changes to the file. It's a good size chuck maxing out at the makerbot's 10cm build surface wide and 7cm tall.
You can design new Jaws to suit your requirement! It is a great tool to have either fitted to a lathe, drill, dremel or just being used to hold items on your bench.
Had an educational time modelling in Carrara and Hexagon which I used to create this thing. I've been using it for a longtime doing fun stuff and mixing it with photography but never tried anything precise.
You are going to need 8 M4-40 cap screws, 8 locking nuts, 1 M7-40(min) hex bolt and nut.
Video of the chuck in action http://youtu.be/94ZhwGUWB5I
The diagram should provide the best explanation for building it. Everything has been designed so that detail and structure is built face up with little overhang.
Use the capscrews on the jaws to lock and loosen the chuck, rotating the grips will move the jaws in and out. It is important to tighten all four jaws!
Safety with anything that can blind you should be taken seriously!