Explanation:
In lathe machine operations, various cutting processes are performed to shape and finish the workpiece. These operations involve the removal of material in the form of chips. However, there is one operation called knurling where chips do not occur.

Knurling:
Knurling is a process of creating a pattern of raised lines on a cylindrical or conical surface. It is usually done to improve the grip or aesthetics of the workpiece. In this process, a knurling tool is used which consists of two hardened steel wheels with inclined teeth. The wheels are pressed against the workpiece and rotated, causing the knurls to be formed.

Why no chips occur in knurling?
During the knurling process, the knurling wheels apply pressure to the workpiece without cutting or removing any material. The teeth on the wheels deform the surface of the workpiece, creating the desired pattern. Since no material is being removed, no chips are produced in this operation.

Difference between knurling and other operations:
- Boring: Boring is an operation where a hole is enlarged or straightened in a workpiece. It involves the removal of material using a cutting tool, resulting in the formation of chips.
- Reaming: Reaming is a process of finishing and sizing a previously drilled hole. A reamer is used to remove a small amount of material from the hole, generating chips in the process.
- Threading cutting: Threading cutting is the process of creating threads on a workpiece. A cutting tool is used to remove material in a helical shape, producing chips as the threads are formed.

Conclusion:
Among the given options, knurling is the only operation where chips do not occur. In knurling, the material is not removed but rather deformed to create a pattern, resulting in the absence of chips.