Acme-Gridley RA-6

The Acme-Gridley RA-6 is a six-spindle automatic screw machine representing one of the most established configurations in North American multi-spindle production history. The RA series, manufactured by Acme-Gridley — a brand with roots in the National Acme Company tradition — built a decades-long reputation in the screw machine industry for producing high-volume precision turned components in steel, brass, and aluminum. CNC-retrofitted and CNC-native RA-6 machines continue to operate in job shops and captive shops across North America, producing fasteners, hydraulic fittings, automotive components, and precision hardware at volumes that single-spindle machines cannot match.

The RA-6 six-spindle configuration provides simultaneous machining at all six positions as the spindle drum indexes through its cycle. Each position performs one or more operations — turning, drilling, tapping, grooving, threading, or cutoff — so that a finished part exits the machine with every drum index. In traditional cam-driven RA-6 machines, each operation's timing and motion are governed by mechanical cams on the main camshaft, a design that rewards long production runs on stable part families. CNC retrofit packages for the RA-6, offered by multiple aftermarket providers, replace or augment the cam system with servo drives and CNC controls, bringing changeover flexibility and programming capability to a mechanically robust platform.

Acme-Gridley RA-6 machines have a particular reputation for structural rigidity and longevity. The cast iron base and spindle carrier were engineered for continuous two- and three-shift production, and well-maintained RA-6 machines often accumulate decades of service life. This mechanical durability is a primary reason the RA-6 platform remains the basis for CNC retrofit investments rather than full machine replacement — the structural bones of the original machine are frequently superior to lower-cost alternatives. Retrofit providers such as Elk Rapids Engineering and others have developed well-documented CNC conversion packages specifically for the RA-series platform.

For shops running the RA-6 in CNC configuration, the machine typically uses a Siemens, Fanuc, or Allen-Bradley control depending on the retrofit package selected. Cross slides and end-working slides are converted to servo drive, with cam-driven motion replaced or overridden by CNC axis commands. The result is a machine that retains the RA-6's mechanical advantages while gaining the program-driven changeover capability needed for shorter runs and more varied part families.

New or rebuilt CNC-configured RA-6 machines are typically priced in the $300,000–$700,000 range depending on condition, retrofit scope, and control specification. This pricing makes the CNC RA-6 one of the most accessible entry points for shops entering the CNC multi-spindle market, particularly in North America where the RA-series installed base and support infrastructure are well established. The machine remains relevant for automotive, hydraulic, and hardware production applications where its 1-inch to 1-5/8-inch bar capacity covers the dominant part diameter range.