Ball screw end machining must match the selected bearing support, with four principal fixity arrangements: fixed-fixed, fixed-floating, floating-floating, and fixed-free [S1].
Fixed ends use angular contact thrust bearings for axial and radial restraint, while floating ends use radial support that permits axial movement to accommodate thermal expansion [S1].
Four Support Arrangements Define System Behavior
End fixity describes how a ball screw is restrained at its ends, and the arrangement directly affects rigidity, buckling resistance, maximum speed, and thermal behavior [S1]. The basic components are the screw, ball nut, and end support bearings, with the bearing choice making the support arrangement a system-level decision rather than an isolated machining detail [S1].
A fixed-end support uses an angular contact thrust bearing that takes axial and radial forces on the screw. Fixed-floating combines one restrained end with one axially free end, while floating-floating places axial freedom at both ends [S1].
A ball screw drawing should therefore identify the end fixity, bearing type, and mating shaft dimensions before the ends are machined.
Fixed Ends Require Angular Contact Geometry
A fixed end uses an angular contact thrust bearing to react axial forces while also supporting radial loads, making it the appropriate support arrangement when the screw must be axially located [S1].
The machining target must match the selected bearing seat rather than merely the nominal screw diameter.
Engineers comparing bearing formats can use the angular contact bearing reference to distinguish this support function from a radial-only floating bearing.
Floating Ends Leave Axial Expansion Free
A floating or simple end uses a single radial ball bearing to support radial loads while allowing axial movement of the screw end [S1]. This movement lets the screw expand or contract with temperature without generating the same axial preload as a fully restrained configuration [S1].
For applications where motor coupling requirements dominate, the ball screw coupling selection: bellows vs jaw decision is separate from end fixity but belongs in the same interface review. The coupling must accommodate the drive arrangement without defeating the intended floating function. A radial ball bearing used for the floating end is distinct from the angular contact bearing used at the fixed end.
Machined End Features Must Match the Assembly
End machining is available for ball screws, lead screws, and Acme screws. Standard and customized end machining are available for ball screws.
Standard end machining is available for fixed bearings BST and fixed bearing arrangements.
Decision Criteria Separate the Four Arrangements
The correct arrangement can be selected by comparing axial restraint, radial support, thermal accommodation, and resulting rigidity. Fixed-fixed provides axial location at both ends and the highest rigidity, but offers the least freedom for axial thermal growth [S1]. Fixed-floating provides one fixed datum and one expansion end, making it the balanced choice for many general-purpose machines [S1].
This comparison is for support architecture, not a substitute for load, speed, and life calculations. Angular contact bearings can carry combined axial and radial loads, while radial ball bearings primarily control radial loading [S1][S3]. Any detailed bearing choice must also consider the load direction, mounting method, required accuracy, and operating speed.
End Machining Is Part of the Support-System Design
Standard end machining is available for common support configurations, and custom machining is used where the standard bearing and motor interfaces do not satisfy the assembly [S4]. A drawing release should therefore carry the screw diameter, accuracy class, end fixity, bearing designation, housing dimensions, coupling interface, and any required end shoulder or retention detail.
Fixed-fixed arrangements suit machines that prioritize rigidity, buckling resistance, and stable positioning, including precision machining applications [S1]. Fixed-floating arrangements suit general machinery where one end must be located but thermal growth must remain manageable [S1]. Floating-floating arrangements suit designs requiring axial freedom at both ends, while fixed-free arrangements suit simpler axes where a free end reduces cost and complexity at the expense of support performance [S1].
For machines with long travel, the axial restraint decision must be reviewed together with ball screw buckling limits for long travel axes. A rigid bearing arrangement cannot compensate for an undersized screw, and a floating end cannot be selected without checking how axial load and buckling are carried elsewhere in the axis.
Specify Ends With the Bearing and Interface
The most defensible machining release defines the complete interface: support arrangement, bearing type, shaft dimensions, shoulder and retention features, drive connection, and tolerance requirements [S2][S4]. For thermal or long-travel axes, the release should also state the expected axial expansion path rather than leaving the machine builder to infer it from the bearing layout.
Trackable design signals include whether both ends are axially restrained, whether each end receives conventional radial support, and whether every machined journal matches the selected bearing and housing dimensions. These checks resolve the main failure mode: a mechanically sound screw end that is dimensionally incompatible with its intended bearing support.