Material
Features
Rotational and Linear Motions: With the combination of an external cylinder with cylindrical raceway and balls incorporated in the retainer, rotary and linear motion in the axial direction is possible simultaneously with rotational motion.
Small Rolling Frictional Resistance: By building a ball with high accuracy into the precisely polished external cylinder, a small rolling frictional resistance and extremely
smooth rolling motion together with reciprocal motion have been achieved.
Small Inertia: The retainer has a high rigidity and light weight so that it has small motion inertia suitable for rolling motion and reciprocal motion in the high-speed operation.
Many Variations: Standard type and heavy load type with different load rating are provided, and each are available with and without seals. You can select an optimal linear
bushing for the specifications of your machine and device.
Recommended Fit
The recommended fit is indicated in Table 1. As the ST series performs rotation and rotary and linear motion at the same time, the internal radial clearance must be smaller when shock load or load accompanied by vibration is applied. Especially when vertical axis application or high accuracy motion is required, it is recommended to set the internal radial clearance at zero or under a slightly-preloaded condition. Excessive preload will shorten the life, so be careful not to set lower limit value of internal radial clearance below the value stated in Table 2.
Raceway
Shafts require heat treatment and ground finish because the surface of shaft is used as raceways.
Recommended Surface Hardness: 58~64 HRC1. Recommended Surface Roughness: 0.2μmRa or lower (0.8μmRy or lower)2.
Recommended value for the minimum effective hardening depth is shown in Table 4.
1 When surface hardness is low, multiply load by rating by hardness factor.
2 Where accuracy standard is low, around 0.8 μmRa (3.2 μmRy) is also allowed.
Stroke Length
For stroke length used, 80% of the maximum stroke length stated in the dimension table is recommended.
Allowable Limit of Speed
The ST series is capable of rotation and rotary and linear motion. However, allowance of velocity for these motions performed at the same time is obtained from the equation (2). Typical values are indicated in Table 3.
Accuracy
Since outer diameter of external cylinder is deformed by stop ring tension, calculate the measurement point from the following equation and use the average diameter value at the point.
W = 4 + L1 / 8 where:
W = distance from the end to measurement point P,
L1 = External cylinder length, mm
Operation
When inserting a shaft, be careful not to shock the ball. After assembling, correct the position of the retainer to be in the center of the external cylinder. After assembling the external cylinder to the housing, insert the shaft softly. Move the retainer as well as the shaft until they contact one side of the surface and stop. Then push the shaft not to damage balls or raceway to the position a half of the maximum stroke length and return it by the same length (a half of the maximum stroke) so that the retainer is positioned regularly at the center of the external cylinder.
Other Info.
Actual Stroke Length should be less than 80% of max. stroke.
Shafts can be made to order.
Mating Shafts should be HRC58-64 with a surface roughness 0.85 or better.
Grease is not pre-packed in the ST series, so please ensure adequate lubrication is used.
Both oil lubrication and grease lubrication are available.
For grease lubrication, the use of high-quality lithium-soap base grease is recommended.
Oil may be fed from the oil hole on the external cylinder provided for lubrication.
DN≥ dp n + 10 S n1 ............... (2)
where, DN : Limit of speed (ref. table 3)
n : No. of revolutions per min. (rpm)
n1 : No. of strokes per min. (cpm)
S : Stroke length (mm)
dp : Pitch circle dia. of balls (mm) (dp = 1.15dr)
dr : Inscribed circle dia. (mm)
This formula is only applicable when n1 ≤ 5,000 and Sn1 ≤ 50,000.