Acme-Gridley RA-8 CNC

The Acme-Gridley RA-8 CNC is an eight-spindle automatic multi-spindle machine representing the largest spindle count in the Acme-Gridley RA series. With eight spindle positions and bar capacity reaching approximately 1-5/8 inches (41 mm) depending on configuration, the RA-8 was engineered for the most complex and demanding high-volume turned parts requirements encountered in the North American screw machine industry. The additional two spindle positions compared to the RA-6 provide process engineers with meaningful additional capacity for complex multi-operation sequences — a critical advantage for parts requiring extensive turning, drilling, tapping, and finishing in a single machine cycle.

Eight-spindle multi-spindle machines require a clear part complexity justification over six-spindle configurations: the additional positions must deliver enough cycle advantage to offset the higher machine cost and footprint. For the RA-8, the typical application profile involves automotive components requiring multiple bore depths at different diameters, hydraulic valve bodies with several cross-drilled ports and threaded connections, or precision hardware with compound geometry requiring a full complement of turning and end-working operations. When a part design genuinely needs seven or eight distinct machining stations, the RA-8 makes cycle engineering straightforward without forcing operations to be combined at individual positions in ways that compromise cycle time or precision.

In CNC-configured form, the RA-8's cross slides and end-working slides are servo-driven, with cam-driven mechanical systems replaced or supplemented by CNC axis control. The control system — typically Siemens Sinumerik or Fanuc in retrofit applications — manages each spindle position independently, allowing programmers to optimize feed rates, infeed motions, and dwell times per station. This is especially valuable on eight-spindle machines where the interdependence of position cycle times on overall machine output is more complex than on six-spindle configurations. The programmer can fine-tune each position's cycle to minimize the bottleneck position that determines the overall machine output rate.

The RA-8's structural platform reflects the same heavy-cast-iron engineering philosophy as other RA-series machines. The eight-spindle drum and spindle carrier are more massive than their six-spindle counterparts, requiring proportionally heavier base castings and more robust drive systems. This structural mass contributes directly to the RA-8's ability to maintain dimensional accuracy across all eight positions during continuous production — vibration isolation between positions is essential when eight simultaneous cutting operations are underway in close proximity.

CNC-configured or rebuilt RA-8 machines are generally priced in the $400,000–$900,000 range, reflecting the added complexity and size versus the RA-6. This pricing remains substantially below new European eight-spindle CNC multi-spindles from manufacturers such as Schütte, Index, or TAJMAC, making the CNC RA-8 an attractive option for North American facilities with existing RA-series expertise and a clear requirement for eight-position capability. Tooling suppliers and service providers with specific RA-8 knowledge are concentrated in the traditional screw machine regions of the Ohio, Michigan, and Connecticut manufacturing corridors.