Needle Rollers, Accessories • Special features required (e.g., controlled stress). • Quantity required. DESIGN CALCULATIONS FOR NEEDLE ROLLER BEARING COMPLEMENTS In the majority of full complement needle roller applications, roller complements of less than 35 needle rollers per row and a ratio of roller length to roller diameter between 8:1 and 4:1 is advantageous. Other combinations of quantity and length-to-diameter ratios of needle rollers have been used successfully. Specifi c design requirements usually dictate the appropriate selection. In general, roller complements for rotating motion should employ a smaller number of larger-diameter needle rollers, while roller complements subjected to oscillating motion (especially under high loads) should employ a larger number of smaller-diameter needle rollers. Oscillating applications with small angular travel encourage the development of fretting corrosion. The best performance under these conditions has been achieved by using the largest practical number of small-diameter needle rollers. CALCULATION OF RACEWAY DIAMETERS It may be convenient to use the Bearing Calculation Form in Table B8-15 on page B-8-14 to calculate the maximum inner raceway and the minimum outer raceway diameters of a bearing. The formula given in Table B8-14 on page B-8-14 can also be used. To assist the designer in making these calculations, the values of K, required for calculation of needle roller complements of 6 through 60 needle rollers, are listed in Table B8-18 on page B-8-15. Values of K for other numbers of needle rollers will be furnished on request or can be calculated from the formula given in Table B8-14 on page B-8-14. Table B8-16 on page B-8-14 lists the suggested values for minimum radial clearance and (Gr min.) minimum circumferential clearance divided by π (cc min./π), to be used for calculating needle roller complements for normal rotating applications where the speeds, loads and shaft defl ections are moderate. Applications with poor lubrication, unusual motion, large misalignment, raceway distortions, load reversals, high speeds, etc., can not be characterized as normal rotating applications. These miscellaneous applications require adjustment of the minimum clearances listed in Table B8-16 on page B-8-14. The factors in Tables B8-17 on page B-8-14 may be used for general guidance in the adjustment of the minimal clearances. For any of the listed miscellaneous applications or any application where abnormal factors such as those listed above exist – and particularly when the inner raceway diameter will exceed 50.800 mm (2.0000 in) – your representative should be consulted for design assistance. CLEARANCES IN NEEDLE ROLLER COMPLEMENTS Needle rollers, supplied in bulk, are generally used to assemble full complement bearings. Successful operation of a full complement of rollers not only requires careful selection of radial clearance, but more importantly, depends on proper circumferential clearance – or the total clearance between rollers. Circumferential guidance in a full complement of needle rollers depends largely on roller-to-roller contact. Too little circumferential clearance causes overheating. Too much circumferential clearance, in a heavily loaded full complement of needle rollers, causes loss of roller guidance and results in roller skew and heavy end thrust. Control of radial clearance and circumferential clearance is infl uenced by the roller diameter tolerance, as well as the tolerances of the inner and outer raceway diameters. END CLEARANCE The total needle roller end clearance, or endplay, normally should be 0.20 mm (0.008 in) minimum per path of needle rollers. NOMINAL-INCH NEEDLE ROLLER TOLERANCES Unless otherwise specified, inch needle rollers are normally manufactured with a tolerance of +0.000 mm -0.005 mm (+0.0000 in -0.0002 in). This tolerance has proven acceptable and ensures satisfactory control of circumferential clearance. The needle roller length tolerance may vary with the end confi guration. The normal roller length tolerance for rounded-end rollers is +0.000 mm -0.508 mm (+0.0000 in -0.0200 in) . JTEKT also manufactures needle rollers with 0.0025 mm (0.0001 in) diameter tolerance. These offer enhanced load-carrying capability and improved control of circumferential clearance. For needle rollers of greater precision, please consult with your representative. Nominal dimensions for typical inch series needle rollers are shown in Table B8-13 on page B-8-12. JTEKT can supply rollers with smaller and larger length-to-diameter ratios for special applications. Rollers with dimensions other than those shown in Table B8-13 on page B-8-12 can be obtained, provided the quantities permit economical production. For example, although the largest needle rollers shown in Table B8-13 on page B-8-12 are 6.35 mm (0.2500 in) [the usual limits for needle rollers], JTEKT can produce quantities of rollers as large as 15.900 mm (0.6250 in) diameter. Your representative should be contacted with the following information about the required needle rollers: • Nominal metric or inch. • Diameter and tolerance (e.g., 3.175 mm, + 0.000 mm, -0.005 mm [0.1250 in, + 0.0000 in, -0.0002 in]). • Length and tolerance (e.g., 14.224 mm, + 0.000 mm, -0.508 mm [0.5600 in, + 0.0000 in, -0.0200 in]). • End form (e.g., rounded-end or fl at-end). • Material (e.g., high-carbon chrome steel). NEEDLE ROLLER BEARINGS B-8-13 B