To maintain precision in linear motion, ball screws must be anchored and supported at both ends. However, the fixed and supported ends perform distinct mechanical functions.
1. The "Fixed-Supported" Paradigm
Fixed Side (BK / EK / FK Models): This unit acts as the primary anchor for the screw, absorbing 100% of the axial (thrust) loads while maintaining zero-backlash positioning. Internally, these blocks house a matched pair of Angular Contact Ball Bearings in a Face-to-Face (DF) configuration. This setup is preloaded against a precision lock nut, creating a rigid anchor that resists thrust from both directions.
Supported Side (BF / EF / FF Models): This unit supports the radial weight of the screw to prevent sagging. It houses a Deep Groove Ball Bearing, where the shaft is secured to the inner race, but the outer race is free to slide laterally within the housing. This "floating" design allows the screw to expand or contract due to thermal friction without inducing axial stress, bowing, or bearing failure.
2. Navigating Form Factors
Support units are available in three distinct geometries to suit various machine designs:
- BK / BF (Pillow Block): The industrial workhorse. This heavy-duty, rectangular block mounts directly to a flat base plate. Ideal for CNC routers and general industrial automation.
- EK / EF (Compact Block): A low-profile, space-saving design. The mounting footprint is highly standardized to align with integrated stepper motor brackets, making it the preferred choice for 3D printers and compact stages.
- FK / FF (Flange Mount): Features a circular housing with an integrated mounting flange. These units are designed to bolt directly onto vertical machine walls or bulkheads, rather than base plates.