Acme-Gridley RB-6

The Acme-Gridley RB-6 is a six-spindle automatic screw machine in the RB series, distinguished from the RA series primarily by its spindle configuration and bar diameter range suited to smaller-diameter precision turning applications. The RB platform established its reputation in North American screw machine shops producing high volumes of small precision components — pins, fasteners, fittings, and electronic hardware — in steel, brass, and aluminum at rates that define the economic model for screw machine production. CNC-retrofitted RB-6 machines remain active in job shops throughout the Midwest and Mid-Atlantic regions of the United States.

The RB-6's six-spindle drum indexes continuously, bringing each workpiece through successive machining positions in a simultaneous cycle. At any given moment, six parts are being machined — turning, drilling, tapping, threading, grooving, and cutoff operations all occurring in parallel. The completed part is ejected at the cutoff position with every drum index, achieving production rates measured in parts per minute for straightforward components and parts per hour for complex multi-operation workpieces. This fundamental multi-spindle advantage over single-spindle turning is the reason the RB-6 and its contemporaries dominated North American precision parts production for most of the twentieth century.

In its original cam-driven form, the RB-6 uses a main camshaft with individual cams governing each cross slide and end-working slide motion. Setup for a new part requires machining or selecting new cam lobes and mechanically adjusting the entire tooling layout — a process that rewards long, stable production runs on well-characterized parts. CNC retrofits for the RB-6, performed by aftermarket specialists with North American multi-spindle expertise, replace cam-driven slide motions with servo drives and add CNC controls, fundamentally changing the changeover economics. Program-driven slide control allows new part programs to be loaded and tooling to be swapped without mechanical cam replacement.

The RB-6's structural design features a heavy cast iron base and spindle carrier that provide the rigidity and vibration damping essential for consistent precision in continuous production. This mechanical robustness is the primary reason RB-6 machines are candidates for CNC retrofit investment rather than disposal when original control systems become obsolete — the machine's structure remains sound long after its original mechanical controls have become a production liability. Well-maintained RB-6 machines have been documented operating for 40 or more years in active production environments.

CNC-configured or rebuilt RB-6 machines are generally priced in the $250,000–$600,000 range depending on condition, retrofit scope, and tooling included. This accessible price point, combined with extensive North American support infrastructure, makes the RB-6 a practical entry into CNC multi-spindle production for job shops that have historically operated single-spindle Swiss-types or that are expanding into higher-volume precision turning. The machine's bar capacity, typically up to 1-1/4 inch depending on configuration, covers the highest-volume segment of the North American screw machine parts market.