To prevent an increase in friction torque in a duplex bearing by the influence of radial thermal expansion of a rotary shaft or inner rings in a spindle device provided with the duplex bearing supporting the rotary shaft in which a pre-load is applied.
A radial distance from the center line of the rotary shaft 20 to the rolling body contact sections of the inner ring tracks is set as r, the contact angle of the inner ring tracks is set as , and a radial space between the rolling body contact sections of the paired inner ring tracks is set as L. The center line of the duplex bearing 30 combined back-to-back with tapered roller bearings 31, 32 is brought into line with the center line of the rotary shaft 20, the radial distance r and the contact angle are set to be the same between the paired inner rings, and the radial space L is set to be 2r/tan so that a pre-load reducing action accompanied by the enlargement of the radial space between the paired inner rings by the thermal expansion of the rotary shaft 20 and a pre-load increasing action accompanied by the enlargement of each inner ring track in the radial direction by the thermal expansion of the rotary shaft 20 and each inner ring are balanced.
MORI MASATSUGU
Torii Kazuhisa
Takayoshi Tagawa
Tounaga Mitsuhiro