Back Gear Unit – Its Construction and Use in ITI Turner Trade

In the ITI Turner trade, controlling the speed and torque of the lathe machine is essential for performing various machining operations. One of the important mechanisms used for reducing speed and increasing torque is the back gear unit. It is commonly found in cone pulley type headstocks. This chapter explains the construction, working, and uses of the back gear unit in detail.

Introduction to Back Gear Unit

The back gear unit is a mechanism used in a lathe machine to obtain lower spindle speeds with higher torque. It is especially useful for heavy cutting operations, threading, and machining large diameter workpieces.

It works in combination with the cone pulley system to provide a wider range of speeds.

Purpose of Back Gear Unit

• To reduce spindle speed
• To increase torque for heavy machining
• To improve cutting efficiency
• To enable accurate thread cutting

Construction of Back Gear Unit

The back gear unit consists of a set of gears mounted in the headstock. The main components include:

• Cone Pulley: Connected to the motor through a belt
• Spindle Gear: Mounted on the spindle
• Back Gears: Intermediate gears used to reduce speed
• Eccentric Shaft: Used to engage or disengage the back gears
• Locking Pin: Locks the cone pulley to the spindle

These components work together to provide two modes of operation: direct drive and back gear drive.

Working Principle

1. Direct Drive (High Speed)

In direct drive, the cone pulley is directly connected to the spindle using a locking pin. The spindle rotates at the same speed as the pulley, providing higher speeds suitable for light work.

2. Back Gear Drive (Low Speed)

In back gear mode, the locking pin is disengaged, and power is transmitted through the back gears. This reduces the spindle speed and increases torque.

The eccentric shaft is used to bring the back gears into mesh with the spindle gear and cone pulley gear.

Function of Back Gear Unit

• Reduces spindle speed
• Increases torque for heavy cutting
• Provides smooth and controlled machining
• Enables accurate threading operations

Uses of Back Gear Unit

The back gear unit is used in various machining operations:

• Heavy cutting operations
• Thread cutting
• Machining large diameter workpieces
• Drilling large holes
• Operations requiring high torque

Advantages of Back Gear Unit

• Provides low speed with high torque
• Improves machining accuracy
• Reduces tool wear
• Simple and reliable mechanism

Limitations

• Manual engagement and disengagement
• Limited speed options compared to geared headstock
• Requires proper maintenance

Precautions While Using Back Gear

• Do not engage back gear while machine is running
• Ensure proper gear engagement
• Lubricate gears regularly
• Check locking pin position

Maintenance of Back Gear Unit

• Keep gears clean and lubricated
• Inspect for wear and damage
• Ensure proper alignment of gears
• Replace worn-out components

Application in Turner Workshop

In the Turner trade, the back gear unit is widely used for operations requiring low speed and high torque. It is especially important in threading and heavy turning operations.

Proper use of the back gear unit improves efficiency and ensures better quality of work.

Importance in Lathe Operation

The back gear unit extends the capability of the lathe by providing a wider range of speeds. It allows the operator to perform different types of machining operations with ease.

Conclusion

The back gear unit is an essential mechanism in the lathe machine. It provides low speed and high torque required for heavy machining operations.

Understanding its construction and use helps trainees operate the lathe efficiently and safely.

In conclusion, proper use and maintenance of the back gear unit ensure improved performance, accuracy, and productivity in the ITI Turner trade.