Overview
ISO 2891:1977 (second edition) specifies key dimensional requirements that ensure interchangeability of centre bases and columns used in special-purpose machines constructed from modular units. This edition cancels and replaces ISO 2891-1973 and was prepared by ISO/TC 39 (Machine tools). The standard defines location methods, preferred sizes and installation tolerances to support modular, repeatable machine-tool construction.
Key Topics
- Scope: Dimensions and location rules for centre bases and columns to permit interchangeability in modular machine-tool assemblies.
- Edition: Second edition (1977) - replaces ISO 2891-1973.
- Location of centre bases: Primary method uses a tenon and slot arrangement; dowels are given as an alternative for locating centre bases.
- Centre base dimensions: Values are specified in a table (table 1). Where lengths over 1 250 mm are required, sizes shall be chosen from the R20 series of preferred numbers. Some dimensions are noted as partial or optional depending on loading height.
- Columns: Column dimensions are given in table 2 and include nominal sizes and fixing arrangements. The published table lists typical nominal sizes (for example 250, 320, 400, 500, 630 mm) and associated pad widths and fixing details.
- Fixings and tolerances:
- Lateral fixing holes spaced in increments of 25 mm (manufacturer’s selection); tolerances between extreme holes: ±0.2 mm.
- Front fixing holes are spaced from the centre line in increments of 25 mm (manufacturer’s selection).
- Typical bolt sizes indicated in the table include M16 and M20 for various nominal column sizes.
- Illustrations: The standard includes sketches (centre base and column) and dimension tables to aid implementation.
Applications
ISO 2891:1977 is intended for designers, manufacturers and integrators of special-purpose machine tools who use modular construction techniques. Practical benefits include:
- Interchangeable modules that reduce bespoke machining and lower lead times.
- Consistent assembly practices across suppliers and models.
- Simplified maintenance and spare-parts management due to standardised dimensions and fixing patterns.
- Design scalability, using preferred-number sizing (R20) for longer elements.
Typical use cases: modular machine frames, custom tooling stations, retrofit columns and centre bases in production lines, and specification of supplier components for machine-tool assemblies.
Related Standards
- Prepared by ISO/TC 39 (Machine tools) - consult committee outputs for complementary machine-tool standards and guidelines.
- This second edition cancels ISO 2891-1973; users should reference the 1977 edition for current dimensional rules and table values.
For implementation, refer to the tables and figures in ISO 2891:1977 for exact dimension values, hole spacing patterns and the specified tolerances.
