Engineering Graphics · Class 12 · Assembly Drawing of Machine Blocks · 3.º Período

Footstep Bearing

Assembling the components of a footstep bearing used to support vertical shafts.

TL;DR:The Footstep Bearing (or Pivot Bearing) is a specialized assembly used to support the bottom end of a vertical rotating shaft. This topic introduces students to a multi-part assembly including the body, a brass bush, and a steel disc (or pad) that takes the vertical thrust. Drawing this requires a deep understanding of how vertical loads are managed and how parts are nested within each other.

• CBSE Learning Outcomes
• CBSE-EG-12.3.3: Draw assembly of a footstep bearing.
• CBSE-EG-12.3.4: Apply proper sectioning to vertical assemblies.

About This Topic

The Footstep Bearing (or Pivot Bearing) is a specialized assembly used to support the bottom end of a vertical rotating shaft. This topic introduces students to a multi-part assembly including the body, a brass bush, and a steel disc (or pad) that takes the vertical thrust. Drawing this requires a deep understanding of how vertical loads are managed and how parts are nested within each other.

In India, footstep bearings are traditionally used in heavy grinding mills and vertical turbine pumps. They represent a unique engineering solution for axial loads. Students grasp this concept faster through structured discussion and peer explanation about why the disc is made of a harder material than the bush and how the 'snug' fit is represented in a sectional view.

Key Questions

1. What is the function of the disc in a footstep bearing?
2. How is the vertical shaft represented?
3. What are the critical dimensions for the body and bush?

Watch Out for These Misconceptions

Common Misconception

Forgetting to draw the clearance at the bottom of the shaft.

What to Teach Instead

Students often draw the shaft touching the very bottom of the housing. It is important to show that the shaft rests on the disc, and there is often a small gap or oil space. Peer-checking against a standard 'clearance' diagram helps correct this.

Common Misconception

Incorrectly sectioning the 'snug' fit parts.

What to Teach Instead

Because the parts fit so tightly, students often miss the double lines. Using a 'magnified view' exercise where students draw just the junction of the body, bush, and disc at a 5:1 scale helps them see the individual boundaries.

Active Learning Ideas

Simulation Game

The Thrust Challenge

Students use a vertical stick (shaft) and try to spin it on different surfaces (sand, wood, a metal coin). They observe which 'pad' allows the best rotation, simulating the function of the steel disc in a footstep bearing.

30 min·Small Groups

Gallery Walk

Sectional Accuracy

Students display their sectional front views of the footstep bearing. Peers check if the 'pin' or 'key' that prevents the bush from rotating is correctly drawn and if the hatching directions for the body, bush, and disc are distinct.

35 min·Whole Class

Think-Pair-Share

The Concave Disc

Why is the top of the steel disc sometimes made slightly concave? Students discuss how this helps in centering the shaft and holding oil, then share their ideas with the class.

20 min·Pairs

Frequently Asked Questions

What is the function of the steel disc in a footstep bearing?

The steel disc (or pad) is placed at the bottom of the bearing to support the entire vertical load (thrust) of the shaft. It is made of hardened steel to resist wear, while the surrounding bush is made of a softer material like brass to guide the shaft's rotation.

How is the bush prevented from rotating along with the shaft?

The bush is usually prevented from rotating by a small 'snug' or a 'pin' that fits into a corresponding notch in the bearing body. In the drawing, this is a small but critical detail that must be shown in the sectional view.

Why is the footstep bearing used for vertical shafts only?

Footstep bearings are specifically designed to handle 'axial thrust', the force acting along the axis of the shaft due to gravity and the weight of the machinery. Horizontal bearings are designed for 'radial loads' (perpendicular to the shaft), making them unsuitable for supporting a vertical shaft's weight.

What are the best hands-on strategies for teaching footstep bearings?

Using 'Exploded View Puzzles' is highly effective. Provide students with cut-outs of the individual parts (Body, Bush, Disc, Shaft) and ask them to 'assemble' them on a board. This physical act of nesting the disc inside the bush, and the bush inside the body, ensures they understand the internal hierarchy before they attempt the complex sectional drawing.