3D printing or additive manufacturing(AM) is any of various processes for making a three-dimensional object of almost any shape from a 3D model or other electronic data source primarily through additive processes in which successive layers of material are laid down under computer control.

A 3D printer is a type of industrial robot. Nowadays, 3D printer is getting more and more popular, accordingly, the demand of 3D printer accessories are also greatly increased.

Linear motion is an essential movement in the 3D printing, so no doubt linear motion components are necessary, such as the linear bearing (alis: linear bushing), linear shaft, usually use LM8UU linear bearing and φ8mm linear shaft.

When a standard-type MCS linear bearing is used with a shaft, inadequate clearance adjustment may cause early bush failure and/or poor, rough travelling. The clearance adjustable linear bearing and open linear bearing can be clearance adjusted when assembled in the housing which can control the outside cylinder diameter. However, too much clearance adjustment increases the deformation of the outside cylinder, to affect its precision and life. Therefore, the appropriate clearance between the linear bearing and the shaft, and clearance between the linear bearing and housing are required according to the application. Below table shows recommended fit of the linear bearing.

Load Rating

Basic Dynamic Load Rating ( C )

This term is arrived at based on an evaluation of a number of identical linear systems individually run in the same conditions, if 90% of them can run with the load (with a constant value in a constant direction) for a distance of 50km without damage caused by rolling fatigue. This is the basis of the rating.

Basic Static Load Rating (Co)

This term defines a static load such that, at the contacting position where the maximum stress is exercised, the sum of the permanent deformation of the rolling elements and that of the rolling plane is 0.0001 time of the diameter of the rolling elements.

Allowable Static Moment (M)

This term defines the allowable limit value of static moment load, with reference to the amount of permanent deformation similar that used for evaluation of basic rated load(Co)

Static Safety Factor (fs)

This factor is used based on the application condition as shown in table 1.

Table 1. Static Safety Factors

Loading Conditions

Low limit of fs

When the shaft has less deflection and shock

1 to 2

When elastic deformation should be considered with respect to pinch load

2 to 4

When the equipment is subject to vibration and impacts

3 to 5

When inserting the linear bearing into the housing, don't hit the side rings(seals), but apply the cylinder circumference with a proper jig and push the linear bearing into the housing by hand or lightly knock it in. (See Fig.1) Then insert the precision linear shaft after linear bearing fully enter into the housing, do be careful not to shock the steel balls. In addition, please note that if two shafts are used in parallel, the parallelism is the most important factor to assure the smooth linear movement. Take care in setting the shafts.

The popular way to mount a linear bearing is to operate it with an appropriate interference. It is recommended, however, to make a loose fit in principle because otherwise precision is apt to be lower. The following examples(Fig.2 to Fig.6) show assembly of the inserted linear bearing in terms of designing and mounting, for reference.

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