ST Shaft
With the ST shaft, used in model ST, balls roll directly on the shaft surface. Therefore, it is necessary to pay much attention to the hardness, surface roughness and dimensional accuracy when manufacturing it.<br/>Since the hardness of the ST shaft has especially large impact on the service life, use much care inselecting a material and heat treatment method.<br/>THK also manufactures high-quality ST shafts. Contact us for details.
Material
Generally, the following materials are used as suitable for surface hardening through inductionhardening.
- SUJ2 (JIS G 4805: high-carbon chromium bearing steel)
- SK3 to 6 (JIS G 4401: carbon tool steel)
- S55C (JIS G 4051: carbon steel for machine structural use)
Hardness
We recommend surface hardness of 58 HRC (≒653 HV) or higher. The depth of the hardened layer is determined by the shaft diameter; we recommend approximately 2 mm for general use. The ST shaft can have a hardened inner ring attached on the shaft raceway.
Surface Roughness
To achieve smooth motion, the surface is normally finished to Ra0.40 or less. If higher wear resistance is required, finish the surface to Ra0.20 or less.
Installation
To install the ST shaft, drive it in to the designated depth. If the clearance is negative, a large driving force is required. However, do not forcibly hammer the shaft. Instead, apply a lubricant on the ST shaft first, and then gradually drive it in with a slight back action.
