How do you represent bearings in an engineering drawing?

Short Answer:

Bearings are represented in engineering drawings using standardized symbols, part outlines, dimensions, and notes. These symbols are used to show the type of bearing, such as ball bearing, roller bearing, or thrust bearing. The drawing may also include a sectional view to clearly display how the bearing is fitted into housing or on a shaft.

To avoid confusion, engineers follow ISO or BIS standards for symbols, and also write bearing codes or reference numbers next to the view. This makes it easy for manufacturers and fitters to choose and install the correct bearing.

Detailed Explanation:

Representing bearings in an engineering drawing

In mechanical systems, bearings are essential components used to support rotating shafts and reduce friction. Since bearings come in different types and sizes, they must be clearly shown in engineering drawings so that the machinist or assembler knows exactly which bearing to use and how to install it.

Representing a bearing in a drawing involves more than just drawing a circle or rectangle. It includes showing the shape, location, mounting method, type, and standard designation. By following standard practices, such as ISO 128, ISO 526, or BIS specifications, bearings can be represented in a way that is easy to read and universally understood.

Common ways to represent bearings

  1. Using standard bearing symbols
  • Symbols for different bearing types are used in simplified views, especially in schematic or layout drawings.
  • Common symbols:
    • Ball bearing → two concentric circles with balls in between
    • Roller bearing → similar to ball bearing but with short lines indicating rollers
    • Thrust bearing → special symbol showing axial load support

These symbols help identify the function and type of bearing without showing detailed parts.

  1. Using sectional views
  • In detailed component drawings, bearings are shown in sectional views.
  • This helps to:
    • Show the inner and outer races
    • Display fit with shaft or housing
    • Show lubrication grooves or seals (if any)

Sectional views are especially important in assembly drawings, where the bearing is one of many parts.

  1. Showing bearing fit and seat
  • A bearing drawing must show:
    • The shaft diameter where the inner race fits
    • The housing bore where the outer race fits
  • Tolerances must be added, such as H7/g6 for shaft or H7/s6 for housing depending on whether it’s a loose, transition, or interference fit.

This helps ensure that the bearing is installed with the correct press or slip fit.

  1. Mentioning bearing part number or designation
  • Most bearings follow standard codes defined by companies like SKF, NTN, FAG, etc.
  • The drawing should mention the bearing type and number, for example:
    • “Deep groove ball bearing 6204”
    • “Spherical roller bearing 22208”

This removes the need to draw the entire bearing in detail and helps procurement and maintenance teams.

  1. Adding assembly or installation notes
  • Include additional information such as:
    • “Grease packed bearing, sealed both sides”
    • “Do not hammer the bearing during assembly”
    • “Press fit bearing into housing using arbor press”

These notes guide the assembler in handling and installing the bearing correctly.

Best practices in bearing representation

  • Always draw the bearing in the correct position inside the machine or housing.
  • Use centerlines and dimensioning standards to show its location accurately.
  • Use partial or broken section views if full details are not necessary.
  • If the same bearing is used in multiple places, number them clearly (e.g., BRG1, BRG2).
  • Refer to bearing datasheets from manufacturer catalogs for dimensions and fits.

Importance of correct bearing representation

  • Prevents assembly errors
  • Ensures correct fit and performance
  • Helps in part identification and ordering
  • Supports machine maintenance and repair
  • Maintains drawing standardization and avoids confusion
Conclusion:

Bearings in engineering drawings are represented using standard symbols, sectional views, dimensioning practices, and specific part codes. These representations help identify the bearing type, its fit with surrounding components, and how it should be assembled. Properly showing bearings ensures smooth manufacturing, accurate part replacement, and reliable machine performance. It is an essential part of mechanical design and documentation.