The Northfield Model 300 is a 3-inch precision air chuck using the same sliding-jaw design as the larger Northfield 870 series. Two master jaws slide on precision-ground ways, driven by an integrated pneumatic piston. The sliding-jaw architecture eliminates the cumulative clearance of scroll or wedge mechanisms — each jaw moves independently with zero backlash, delivering 0.0001" TIR repeatability as standard. The chuck body is Class 80 ductile cast iron with an aluminum and stainless steel cylinder housing sealed by O-rings.

How does adjustable clamping force work?

Air pressure to the integrated cylinder is regulated from approximately 5 to 100 psi, producing 20 to 395 lbf per jaw. This linear relationship between pressure and force means the operator can reduce clamping pressure for thin-walled rings or fragile materials without changing chucks. Both air-clamp/spring-open and spring-clamp/air-open actuation modes are available — the former for production turning where air failure should release the part, the latter for applications where the part must remain clamped during power loss.

Stationary vs. rotating use

Despite the "300THS" designation for the through-hole stationary variant, the Model 300 is rated for both stationary applications (grinding, inspection, assembly fixtures) and rotating use on lathe spindles up to 6,000 rpm. The through-hole (0.25 inch) accommodates small-diameter bar stock or coolant feed.