NSK45TAC100ADBBall Screw Support Bearing Matched Pair 45x100x20 mm 60° Back-to-Back 2 Pcs

Product Description

What this part is

A back-to-back matched pair of ball screw support bearings from NSK’s TAC series: thrust-biased angular contact ball bearings built specifically to locate the end of a ball screw. Bore 45 mm, outside diameter 100 mm, width 20 mm, with a 60° contact angle.

Decoding the order code

In this NSK scheme the leading number is the bore in millimetres and the number after TAC is the outside diameter, so 45TAC100 reads directly as 45 mm bore in a 100 mm outside diameter. TAC identifies the ball screw support family, A the internal design series, and DB a back-to-back matched pair. This convention differs from the ISO 70xx and 72xx series, where the last two digits encode the bore rather than stating it. The carton also carries MM45BS100, the Timken-scheme designation for the same bearing, in which MM…BS denotes a 60° ball screw support bearing — which is where the contact angle is sourced from.

What a 60° contact angle buys

Sixty degrees is far steeper than the 15° to 40° range used on general-purpose angular contact bearings, and it is the defining feature of the ball screw support family. Axial capacity and axial stiffness rise steeply with contact angle while radial capacity falls, so a 60° bearing is close to a pure thrust bearing. That matches the duty exactly: a ball screw takes almost all of its load axially, and the radial load at the screw end is small.

The consequence for substitution is direct. An ordinary 70- or 72-series angular contact bearing of the same 45 x 100 x 20 mm envelope will physically fit the same seats but carries a fraction of the axial stiffness, so an axis built on one loses positioning accuracy under thrust. The equivalent families to match against are the RHP BSB series, FAG’s 7602 series, NTN’s BST series and Timken’s MM…BS series.

What the back-to-back arrangement buys

Axial stiffness at the screw end sets positioning accuracy on a machine axis: a screw located on a soft or unpreloaded support deflects under thrust, and that deflection appears directly as lost motion. A back-to-back pair takes thrust in both directions, one bearing per direction, and its diverging load lines give the pair a wide effective span and therefore moment stiffness — resistance to the screw journal tilting rather than merely translating. The pair is ground as a matched set, so clamping the rings solid develops the intended preload with no shimming.

Quantity and configuration

2 Pcs, supplied as one back-to-back matched pair. Open on both faces.

Fitting notes

The pair seats in the screw’s support housing with the thrust faces oriented as the face marks indicate, and the two pieces stay together because the matched grind belongs to the pair. The locknut on the screw journal is drawn up against the inner ring face so clamping load passes through the rings and never through the ball complement. Seats at this tolerance class are ground and measured.

Interchange guidance

MM45BS100 is the Timken-scheme designation for this bearing. Related sizes rather than interchanges: other bore and outside diameter combinations in the TAC series, other tolerance classes, and the DF face-to-face and DFD, DBD and triplex arrangements of the same envelope, which are ground to different set stack heights. Ordinary angular contact bearings of this envelope in the 70 or 72 series are a different family. Individual pieces separated from a matched pair are not equivalent to pair stock.