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

Open Bearing and Bushed Bearing

Drafting the assembly of open and bushed bearings showing all internal and external features.

TL;DR:Open Bearing and Bushed Bearing introduce students to the world of assembly drawings. A bearing is a machine element that supports a rotating shaft and reduces friction. In this topic, students learn to draw the assembly of a simple 'block' bearing and a more complex 'bushed' bearing where a brass or bronze bush is inserted to act as a sacrificial wear surface. This requires careful alignment of multiple parts and the use of sectional views to show internal details.

• CBSE Learning Outcomes
• CBSE-EG-12.3.1: Assemble and draw open bearing.
• CBSE-EG-12.3.2: Assemble and draw bushed bearing.

About This Topic

Open Bearing and Bushed Bearing introduce students to the world of assembly drawings. A bearing is a machine element that supports a rotating shaft and reduces friction. In this topic, students learn to draw the assembly of a simple 'block' bearing and a more complex 'bushed' bearing where a brass or bronze bush is inserted to act as a sacrificial wear surface. This requires careful alignment of multiple parts and the use of sectional views to show internal details.

Bearings are the heart of Indian industry, found in everything from ceiling fans to massive railway locomotives. This topic teaches students about maintenance and the choice of materials in engineering. This topic comes alive when students can physically model the patterns of assembly by taking apart a simple bearing block and seeing how the bush fits snugly into the housing.

Key Questions

1. How is the bush secured in the bearing block?
2. What sectioning techniques are used for bearings?
3. How do we align the base and the shaft hole?

Watch Out for These Misconceptions

Common Misconception

Hatching the shaft in an assembly section drawing.

What to Teach Instead

Standard convention dictates that solid shafts, bolts, and nuts are not sectioned (hatched) even if the cutting plane passes through them. Peer-review sessions using a 'Hatching Checklist' help students remember this important rule of engineering graphics.

Common Misconception

Drawing the bush and the body as a single piece.

What to Teach Instead

Students often forget the line separating the bush from the bearing body. Using two different colored pencils in initial sketches to represent different materials helps them remember to show the interface between the two parts.

Active Learning Ideas

Stations Rotation

Assembly Sequence

Station 1: Identify parts of a bushed bearing (Body, Bush, Shaft). Station 2: Practice drawing the 'snug fit' of the bush. Station 3: Determine which parts should be hatched in a sectional front view.

50 min·Small Groups

Think-Pair-Share

Why use a Bush?

Students discuss: 'Why not just put the shaft directly in the cast iron block?' They explore the concept of 'sacrificial parts' and share how this saves money in industrial maintenance.

20 min·Pairs

Inquiry Circle

Sectioning Rules

Students are given a 3D view of an open bearing. They must work together to decide where the cutting plane should pass to show the oil hole and the base bolts most clearly, then sketch the resulting section.

35 min·Small Groups

Frequently Asked Questions

What is the difference between an open bearing and a bushed bearing?

An open bearing is a simple cast iron block with a hole for the shaft, used for low-speed applications. A bushed bearing includes a separate 'bush' (usually made of brass or bronze) inside the hole. The bush reduces friction and can be replaced when worn out, extending the life of the main bearing block.

Why is an oil hole provided in a bearing?

The oil hole allows for lubrication (oil or grease) to be supplied to the interface between the rotating shaft and the stationary bearing or bush. This lubrication is essential to reduce friction, prevent overheating, and minimize wear and tear.

How do you show different materials in a sectional assembly drawing?

In a sectional view, different materials are indicated by changing the direction or spacing of the hatching lines. For example, if the bearing body has hatching lines at 45 degrees to the right, the bush should have hatching lines at 45 degrees to the left.

How can active learning help students understand bearings?

Active learning through 'Virtual or Physical Disassembly' helps students see the 'fit' between parts. By physically placing a 'bush' into a 'housing', students understand that these are distinct components. This clarity translates into better drawings where they correctly identify and represent the boundaries between different parts in an assembly.