Shaper mechanism — changing stroke length In a standard shaper with crank-and-slotted link (Whitworth) mechanism, how can the length of ram stroke be increased?

Introduction / Context:
In shaping machines, the ram executes a reciprocating stroke produced by a crank-and-slotted link mechanism. Understanding which dimension governs stroke length is fundamental for setup and maintenance.

Given Data / Assumptions:

• Whitworth quick-return mechanism is used.
• Stroke length is approximately twice the crank radius.
• Other link lengths mainly affect timing (quick return) rather than stroke magnitude.

Concept / Approach:
The ram stroke is generated by converting rotary motion of the bull gear to reciprocation via a crank pin and slotted link. The peak-to-peak displacement equals about 2 * crank radius. Therefore, increasing the crank radius directly increases stroke.

Step-by-Step Solution:
Relate stroke length S to crank radius r: S ≈ 2r.To increase S, increase r, which is the centre distance from bull gear centre to crank pin.Hence, select the option that increases this centre distance.

Verification / Alternative check:
Machine manuals show adjustable crank pins: moving the pin outward on the bull gear face plate increases stroke; moving inward decreases it.

Why Other Options Are Wrong:
Reducing the centre distance decreases stroke; modifying slotted link/arm length changes velocity characteristics, not stroke magnitude; clapper box angle affects tool relief on return, not stroke length.

Common Pitfalls:
Confusing quick-return ratio adjustments with stroke length; they are related but controlled by different geometric parameters.

Final Answer:
Increase the centre distance between the bull gear centre and the crank pin (i.e., increase crank radius)