A CNC machine is a mechatronics system since the machine tool which is a mechanical system is incorporated or integrated with electronic controls for its different drives and computer system for interfacing the software with the mechanical and electronic system. Hardware or electronic circuits controls the motions of various drives.
The basic design of conventional machine tools are not suitable for CNC machines because CNC machines have to meet additional requirements.
a. The manual handwheel controls of conventional machine tools are replaced by axis drive motors.
b. To minimize the size of these motors the friction between sliding surfaces have to beconsiderable reduced or prevented if possible.
c. Higher cutting speeds, feeds and improved tooling system induces high multi directional forces which demands for proper machine structure.
d. Much of the time in CNC machines are spent in cutting operations, allowing very little time for setting and change over of jobs.
e. This means high metal removal rate and faster wear of guide ways, lead screws, gears etc.
f. This calls for an efficient system for swarf removal from the machining place and lastly the safety of the operator.
Element of CNC Machine
In order to cater for the above requirements special consideration should be exercised while designing the different elements of the CNC machine. The important elements of a CNC machine are,
a. Machine Structure
b. Guide ways / Slide ways
c. Spindle Mounting
d. Drive Units (Elements of transmission and positioning of slides)
e. Tool and work holding devices
f. Measuring systems
g. Swarf removal
h. Safety Devices.

Guide Ways
Guide ways or slide ways are provided on machine structure to provide
a Movement of slides which carry the tool, the job or the tool post
b To maintain proper alignment of sliding or guided part at all relative positions.
c To absorb all static and dynamic loads.
Guide ways may be an integral part of the machine structure or may be mounted separately on the structure. These guide ways may be horizontal, vertical or inclined, but vertical and inclined guide ways are preferred so that the chips produced during cutting operation do not get collected on the guide ways.
The dimensional accuracy, shape and surface finish of the component or part produced depend on the accuracy of the movement of the slide, geometric (shape) and kinetic accuracy of the guide ways. The geometric relationship of the slide and the guide ways with reference to the base of the machine determines the geometric accuracy of the machine. The kinetic accuracy of the guide ways depends on the straightness, flatness and parallel. Error in any of the above leads to kinetic inaccuracy. Kinetic inaccuracies may result in variety of tracking errors such as pitch, yaw and roll of the slide that are difficult to measure and correct. Errors may also arise due to wear in the guide ways and slides over a period of usage resulting in inaccurate movement and positioning of the slide.
Desired characteristics of guide ways
a. Should possess large stiffness to give exact alignment for guided parts in all positions and also under the effect of operational forces.
b. Minimum wear and provision for compensation of wear developed after usage.
c. Ease of assembly and economy i n manufacturing.
d. Provision for adjustment of play.
e. Geometric and kinetic accuracy.
f. High stiffness and less deformation under the influence of cutting forces.
g. 'Freedom from unnecessary restraint.
Factors influencing the design of guide ways
a. Stiffness and alignment of guided parts
b. High wear resistance and provision for compensation of worn out parts.
c. Effective lubrication and efficient lubricating system.
d. Effective coolant and efficient coolant system
e. Minimum or no chip getting entrapped.
f. Ease of assembly and economy of manufacture
g. Freedom from unnecessary restraint.
h. Velocity of slide.
i. Provision of adjustment of play
j. Protection against swarf and damage.
k. Protective guards to safe guard the guide ways against accidental damages (Mechanical abuse).
The above factors may vary in importance depending upon the particular application and hence selection of type of guide ways and their shape are quite critical in some applications. To import uniform frictional force in the guide ways the driving mechanism should be properly and correctly located relative to the forces of the guide ways.
Types of guide ways.
Guide ways are broadly classified into three types. They are