Selecting the appropriate linear bushing.

- When to use a single, double or long bushing
- Selecting the right material and surface treatment for your application

(1) Bearing length of linear bushing and bushing performance

There are four types of bearing lengths. Three types are designed by Misumi as follows; [1] Single, [2] Double and [3] Long. The fourth type [4] is custom design (by purchaser) and usually incorporates two single bushings. The difference of these bearing lengths affects the bearing performance in two ways:
a) Load Resistance.
b) Guidance Accuracy.

a) Relation between bearing length and load resistance

When the bearing length is increased (short to long), the number of the bearing balls inside the bushing is increased, resulting in smaller load at the contact point of each ball.

This is found from the fact that the rated load of linear bushings [1], [2] and [3] increases according to the length of the linear bushing.

Therefore, using a linear bushing with a long bearing length can allow for an increase in the allowable load. (Practically, this equates to longer life and improved reliability. ([Fig. 1]))

b) Relationship between bearing length and guidance accuracy

As the bearing length is increased, the guidance accuracy improves for the following reasons:

a) Guidance misalignment of the rail (shaft) is averaged thereby improving the precision. (for information on this 'averaging effect'*, see note and [Fig. 2])

b)Misalignment due to the clearance from the rail (shaft) is reduced; which improves the precision. ([Fig. 3])

In this way, increasing the bearing length increases the allowable load and the guidance accuracy. [Fig. 4] shows how custom designed linear bushing, that incorporates two single linear bushings is used in high precision application.

(2) Calculating rail (shaft) deflection ([Fig. 5])

The shaft deflection for a linear motion composed of a linear bushing and a shaft can be calculated using the following formula:

(3) Materials and surface treatment characteristics and applications

Materials, surface treatment and applications of linear bushing are as shown in the table below:



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