The BISON 3105-6 is a 6-inch 2-jaw self-centering scroll chuck for manual lathes. While most general-purpose turning uses 3-jaw or 4-jaw chucks, the 2-jaw configuration is specifically engineered for workpieces with two dominant parallel gripping surfaces — square bars, rectangular blocks, and flat-sided castings — where opposing-jaw contact provides the most stable and distortion-free clamping.

What are 2-piece soft jaws and why do they matter?

The chuck ships with 2-piece soft jaws: a hardened base jaw driven by the scroll, and an unhardened top jaw bolted to it. The top jaw is designed to be machined — bored, turned, or milled — to match the exact profile of the workpiece. This custom contouring achieves full-surface contact across the gripping face, maximizing clamping force distribution and minimizing part distortion. Once machined, the jaws maintain their accuracy for the life of that specific production run. Replacement top jaw blanks are inexpensive and widely stocked.

Mounting and setup

The 3105-6 uses a plain back mount conforming to DIN 6350, the European standard for cylindrical-centering chuck mounting. This requires an adapter plate matched to the lathe spindle nose — common on toolroom and engine lathes. Mounting screws and a chuck wrench are included in the box. The through-hole permits bar and shaft work within the bore capacity of the 6-inch frame.