What is a treadle linkage?

A treadle is a foot-operated lever that rocks back and forth about a pivot. A connecting rod and crank turn the rocking into rotation, as on a treadle sewing machine.

Why might a bell crank be fitted to the rod of a short-stroke cylinder?

The cylinder acts on the short arm, so the long arm moves further than the rod. The output then travels further at a lower force and at 90° to the cylinder.

What is meant by aligned shafts, and why does alignment matter?

Aligned shafts share a common centre line where they are joined. Misalignment causes vibration, bearing wear and coupling failure.

CCEA A-Level Technology and Design 8900

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Mechanical and Pneumatic Systems

Toggles, treadles, shafts and couplings

3 things to know
A2 1

Overview

Toggle and treadle linkages, bell cranks with cylinders, shaft alignment, rigid and flexible couplings, universal and constant velocity joints, sliding and Oldham couplings.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

What is a toggle linkage?

Key term

Why does a toggle clamp lock firmly in place?

Process

Give two uses of a toggle mechanism.

Questions from this subtopic

Each one with the model answer underneath.

1
What is a toggle linkage?
Model answer
A toggle linkage has two links joined at a pivot that are pushed nearly into a straight line. A small force at the joint then produces a very large force at the ends.
2
Why does a toggle clamp lock firmly in place?
Model answer
The links are pushed slightly past the straight, over-centre position against a stop. Any force from the workpiece then pushes the linkage further closed rather than open.
3
Give two uses of a toggle mechanism.
Model answer
Toggle clamps hold work on jigs and welding fixtures. Stone crushers also use toggle action to apply very large forces.
4
What is a treadle linkage?
Model answer
A treadle is a foot-operated lever that rocks back and forth about a pivot. A connecting rod and crank turn the rocking into rotation, as on a treadle sewing machine.
5
Why might a bell crank be fitted to the rod of a short-stroke cylinder?
Model answer
The cylinder acts on the short arm, so the long arm moves further than the rod. The output then travels further at a lower force and at 90° to the cylinder.
6
What is meant by aligned shafts, and why does alignment matter?
Model answer
Aligned shafts share a common centre line where they are joined. Misalignment causes vibration, bearing wear and coupling failure.

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