Anti-friction Linear motion guide ways

Metal to metal contact has a relatively high coefficient of friction and results in higher wear and heat generation. To minimize this, anti-friction linear motion guide ways are used on the CNC machine tools to:

·         Reduce to amount of wear

·         Reduce friction

·         Reduce heat generation

·         Improve the smoothness of the movement

Advantages of Anti-Friction guideways

·         Low frictional resistance

·         No stick slip

·         Assembly time is minimized

·         Ease of availability

·         High load carrying capacity

·         Heavier preloading possibility

·         High traverse speeds

Disadvantages of Anti-Friction guideways

·         Lower damping capacity

Examples of Anti-Friction guideways

·         Non re-circulating ball or roller cages

·         Re-circulating ball bushings

·         Re-circlulating roller bearings

·         Cross roller bearings

·         Linear motion guides

Different Shape of Guide Ways

Most commonly used shape of building elements of slide ways are

1.      V-Type

2.      Flat type

3.      Dove Tail Type

4.      Circular or cylindrical type

The selection of the proper shape is based on the magnitude and direction of the load to be carried, position of transmission, wear characteristics ad provisions for wear adjustments, ease of assembly and economy in fabrication, effective lubrication and the easy chip disposal.

All the four types of shapes have their own merits and demerits and thus some times it becomes desirable to use a combination of these slide ways on the machine tools.

1) V-Type Guide Ways:

Slide ways are advantageous because of the automatic adjustment the to gravity action which always keeps the surface in contact, thus the possibility of any play is eliminated. In addition, the wedging action due to cross winding is also prevented and there is no possibility of chips falling on the V-surface and getting entrapped into it. It has no tendency to accumulate dust. The Disadvantages of V-Type guides is that it wears away rapidly due to lack of bearing surface and is difficult to manufacture.

2) Flat Type Guide Ways:

Slide ways are simple in construction and offer quite a large bearing area to the moving parts. Therefore to overcome the disadvantage of V-type slide ways by the advantages of the flat type slide ways. Separate guides are provided for the saddle and tail stock movements so that any wear caused by the saddle movement does not affect the height of tail stock centre.

The flat bed guides the saddle by the side guides and in order to prevent lifting movement the retaining pieces are fitted below the flat bed.

3) Dove Tail Type Guideways:

This type slide ways are preferred when location of the moving parts is considered essential. These are generally used for milling machine tables, saddles and knees. In dove tail type slide ways, adjustment for wear can be made by parallel blocks pushed by set screws.

DOVE tail slide ways occupy small space. A Gib is provided. So that it can adjusted to ensure that the two element of the slide are a good sliding fit.

4) Cylindrical Type Guideways:-

This slide fulfills the condition of kinematic principles being fully constrained. These guides are used in the pillar or radials drilling machines.

Clearance between mating surfaces of slide ways are inevitable because of wear and manufacturing imperfections. Clearance between flat ways may be controlled periodically by means of there gibs or strips.

Stick-slip motion of slide ways caused by frictional resistances between the sliding surfaces can be controlled by using anti-friction ways.