In centreless grinding, the workpiece centre is located above the line joining the two wheel centres. This positioning is crucial for the effective functioning of the centreless grinding process. Let's understand why this is the case.

The Basics of Centreless Grinding:
Centreless grinding is a machining process used to remove material from a workpiece. It does not require a central axis, unlike traditional grinding methods. In this process, the workpiece is supported by a workblade and is positioned between two grinding wheels: the regulating wheel and the grinding wheel.

The Role of the Regulating Wheel:
The regulating wheel plays a critical role in centreless grinding. It controls the rotational speed and feed rate of the workpiece. The workpiece is fed between the grinding wheel and the regulating wheel, and the regulating wheel applies pressure to the workpiece, causing it to rotate. This rotation, combined with the grinding action of the grinding wheel, removes material from the workpiece.

The Importance of Workpiece Centre Position:
The position of the workpiece centre is crucial in centreless grinding because it determines the stability and accuracy of the process. The workpiece centre should be located above the line joining the two wheel centres for the following reasons:

1. Stability: Placing the workpiece centre above the line ensures that the workpiece is properly supported by the workblade and the regulating wheel. This positioning prevents any tilting or instability during the grinding process, resulting in a more stable and controlled grinding operation.

2. Accuracy: The workpiece centre needs to be accurately positioned to achieve precise grinding results. Placing it above the line allows for better control of the workpiece rotation and feed rate, leading to accurate material removal and consistent grinding results.

3. Uniform Grinding: When the workpiece centre is above the line, it ensures that the grinding action is evenly distributed across the workpiece surface. This helps in achieving uniform material removal and prevents uneven grinding or surface irregularities.

4. Wheel Wear: Positioning the workpiece centre above the line also helps in minimizing wheel wear. It allows for better contact between the grinding wheel and the workpiece, reducing the chances of wheel glazing or uneven wear.

In conclusion, in centreless grinding, the workpiece centre should be positioned above the line joining the two wheel centres for stability, accuracy, uniform grinding, and to minimize wheel wear. This positioning ensures optimal performance and better control over the grinding process, resulting in high-quality finished products.