Acme-Gridley RB-8

The Acme-Gridley product line covered multiple frame sizes: the RB-6 (6-spindle, smaller bar capacity), RB-8 (8-spindle, mid-range), and larger models up to 4.5 in bar capacity. The number in the model designation relates to the spindle count (6 or 8) or bar capacity depending on the specific model family. The RB-8 is the most commonly encountered and was produced in the highest quantities. Bar capacity varies by model variant - the standard RB-8 handles approximately 52 mm (2 in) bar, while larger variants accommodate 60 mm (2.375 in). When evaluating a specific RB-8, verify the spindle bar capacity with the serial number and production records.

For a simple 3-operation part with 2-second cam cycle: 6-spindle machine produces 1 part per cycle (one part completes as all 6 spindles index) = 1,800 parts/hour. 8-spindle machine at same 2-second cycle: 1 part per cycle = 1,800 parts/hour. Wait - the throughput advantage comes from distributing more complex operations across more stations, enabling shorter cycle times. With 8 stations instead of 6, complex parts that would require combined operations at a single 6-spindle station can be separated across 2 stations, reducing the controlling station cycle time. For a complex part: 6-spindle cycle bottleneck at 3 seconds = 1,200 parts/hour; 8-spindle with same operations across 8 stations: bottleneck reduced to 2 seconds = 1,800 parts/hour. The 8-spindle advantage grows with part complexity.

The Acme-Gridley brand is no longer in active production, but parts continue to be available through: (1) Specialty screw machine parts suppliers (National Machinery Exchange, Janda Company) who stock RB-8 specific parts from original inventories; (2) Machine rebuilders who maintain parts inventory as part of their rebuild business; (3) Secondary market from shops liquidating Acme-Gridley equipment (good source of tooling, cams, and mechanical components); (4) Domestic machine shops capable of fabricating wear parts from drawings. Most mechanical components (cross-slides, cam followers, spindle components) can be fabricated by a competent machine shop if original parts are unavailable. Electronic components are not used in mechanical cam machines.

RB-8 operation requires two skill levels: (1) Machine operator - loads bar stock, monitors production, changes worn tooling, checks parts. Basic training takes 1-2 weeks. (2) Setter - designs cam profiles for new jobs, grinds cams, sets all tooling positions, troubleshoots quality issues. Setter training takes 2-5 years of apprenticeship to develop full competency. Setter skills are rare and valuable - experienced Acme-Gridley setters command premium wages. Shops acquiring RB-8 machines without an in-house setter capability must contract setter services for new job setups. Some screw machine associations (Precision Machined Products Association) maintain directories of contract setters and training resources.

A complete RB-8 rebuild involves: (1) Disassembly and cleaning; (2) Spindle rebuilds (bearings, spindle sleeve replacement where worn); (3) Cross-slide reconditioning (way scraping or grinding to remove wear); (4) Camshaft and cam follower inspection; (5) Cam spindle assembly inspection; (6) End-working spindle rebuild; (7) Bearing replacement throughout; (8) Paint and reassembly. Rebuild cost from a specialist rebuilder: $30,000-$80,000 depending on machine condition and scope. A rebuilt RB-8 from a reputable rebuilder provides essentially new machine performance at a fraction of new CNC multi-spindle cost. For high-volume shops committed to cam multi-spindle production, a rebuilt RB-8 at $50,000-$100,000 total cost (machine + rebuild) is compelling versus $600,000+ for a new CNC multi-spindle.