The cutting speed of the tool in a mechanical shaper is
Maximum at the middle of the cutting stroke
Shaper Cutting Speed: Understanding Velocity Variation
A mechanical shaper is a machine tool used for producing flat surfaces. It operates with a reciprocating motion of the tool, which moves linearly across the workpiece during the cutting stroke, while the workpiece is usually held stationary or given a small intermittent feed motion. The return stroke is generally faster and does not involve cutting.Shaper Mechanism and Velocity Profile
The cutting stroke of a shaper is typically driven by a mechanism that converts rotary motion into reciprocating linear motion. Common mechanisms include the crank-and-slotted-lever mechanism (like the Whitworth mechanism).
During the cutting (forward) stroke, the velocity of the tool (and the ram carrying it) is not constant. It starts from zero at the beginning of the stroke, increases to a maximum value, and then decreases back to zero at the end of the stroke.
The cutting velocity, denoted as $v$, varies throughout the stroke. The rate of change depends on the specific mechanism used. For standard mechanisms like the quick-return type:
- The velocity is minimum (zero) at the start of the cutting stroke.
- The velocity increases as the stroke progresses.
- The velocity reaches its maximum value approximately at the middle of the cutting stroke. This is typically when the driving crank is roughly perpendicular to the line connecting the crank center and the pivot.
- The velocity decreases towards the end of the cutting stroke, becoming zero again.
Velocity Comparison During Cutting Stroke
| Position in Stroke | Cutting Velocity ($v$) |
|---|---|
| Beginning of Stroke | Minimum (approaching zero) |
| Middle of Stroke | Maximum |
| End of Stroke | Minimum (approaching zero) |
Conclusion on Maximum Cutting Speed
Based on the typical operation of a mechanical shaper, particularly those employing crank-driven quick-return mechanisms, the cutting speed of the tool is highest when it is in the middle of its forward cutting stroke. This is a direct consequence of the kinematics of the drive mechanism converting the constant angular velocity of the crank into a varying linear velocity for the ram.
Important Questions from Machining Processes and Machine Tools
For which material, the cutting speed will be maximum for machining?
Which of the following wear mechanisms is primarily responsible for the formation of crater wear on the rake face of a cutting tool?
The angle produced between the face of the tool and plane parallel to the base of the cutting tool is known as _______.
- In chemical machining, the etch factor is expressed as:
Which of the following relationship between shear angle ϕ, friction angle β and cutting rake angle α is known as Lee and Shaffer analysis
