Bearing Selection Fig. 1-8 On-apex design results in true rolling motion at all points along the roller body.
Precision Tapered Roller Bearing Types The size range of Timken precision bearings starts from less than 20 mm bore and extends to over 2000 mm OD, depending on bearing type. The most popular tapered roller bearing types made in precision classes are the single row bearings: Timken types TS and TSF as shown in chapter 2. These bearing types are supported by a range of special bearings which have been designed for machine tool applications, such as the variable preload Hydra-Rib bearing, the high speed TSMA bearing, and the compact TXR crossed roller bearing – which are available only in precision classes. Timken also offers a selection of 2-row precision tapered roller bearings: types TDO and TNASWH. To further minimize the influence of variations, Timken offers a level of precision bearing manufacture so tightly controlled that it goes beyond the grade levels of both ISO and ABMA standards. Timken’s Precision Plus™ line offers (inch-nominal) 000 and (metric-nominal) AA level tapered roller bearings in various sizes and styles.
Crossed Roller Bearings
A crossed roller, or TXR bearing, is effectively two sets of bearing races and rollers brought together at right angle to each other, with alternate rollers facing opposite directions, within a section height not much greater than that of a single row bearing. Also, the steep angle, tapered geometry of the bearing causes the load-carrying center of each of the races to be projected along the axis, resulting in a total effective bearing spread many times greater than the width of the bearing itself. Because of the ability of the crossed roller bearing to withstand high overturning moments, it is ideal for the table bearing of machine tools such as vertical boring and grinding machines, and numerous other pivot and pedestal applications where space is limited or the lowest possible center of gravity of a rotating mass is required. Crossed roller bearings are available in two precision classes: • Metric system Class S and P • Inch system Class 3 and 0 The most usual form of the bearing is type TXRDO, which has a double outer race and two inner races, with rollers spaced by separators.
TXRDO
Fig. 1-9 Small seating force from the inner race rib keeps rollers aligned on the raceway.
TXR Timken Super Precision Bearings / 17
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