Although there are several different options when it comes to CNC equipment, most used today are designed to form a straight line motion that is 100% accurate.  However, many tools associated with CNC equipment are also capable for creating circular motions.  In this case, applications would involve a radii being formed on the work piece, which goes between the turns and faces, as well as milling radii on contours for machining the center work piece.  For CNC equipment to produce a circular motion, circular interpolation is required, which consists of the controlling striving to create results closest to the path as possible.

One of the primary changes seen with CNC equipment is that manufacturers are making it possible for controls to be programmed easier.  For instance, if a unique type of movement were required, the needed interpolation type would be produced by the control manufacturer.  One example of this is that for threat milling, the CNC equipment would have the ability to move circularly along two axes simultaneously while going in a linear fashion so the thread’s helix is machined correctly.

Remember, CNC equipment is far more flexible and diverse than ever before but it still produces three primary types of motions.  However, it is common for additional motions to be provided, which would depend on the exact piece of CNC equipment.  Regardless, the following are the three most fundamental types of motions that are found in all CNC equipment.

1.    Rapid Motion – This is also referred to as “positioning”, which helps to command the CNC machine’s fastest rate possible.  With this motion, down-time or non-productive time while cycling occurs is minimized.  Typically, Rapid Motion is used to change cutting positions, move clamps, and any other non-cutting motion associated with the program.
 
2.    Straight Line – This CNC equipment motion is also called “linear interpolation”, which lets the programmer tell the machine to make a perfectly straight line and dictate the feed rate for each movement.  With the Straight Line motion, drilling, milling straight surfaces, or turning a straight taper, face, or diameter would be possible.

3.    Circular Motion – The last motion for CNC equipment is also known as “circular interpolation”.  With this, the equipment could create a circular pattern, which is often used to create radii during the machining phase.  Additionally, the programmer of the CNC equipment would have the ability to determine arc radius.

All three motions for CNC equipment are modal, meaning until changed, they stay the same.  In addition, the three motions have an end-point, which is determined with each motion command.