Open bearing

The essentials

An open bearing is one of the simplest shaft supports. Its body, usually of cast iron, has a base with holes for foundation bolts and an open, semicircular seat at the top. A brass or gunmetal liner (bush or step), shaped as a half-round shell, sits in this seat and the shaft rests on it. Because the top is open, the shaft can be lowered into the bearing from above instead of being threaded in from one end. Such bearings suit slow-moving shafts where the load acts downward.

Key points

• Main parts: body (with base and open seat) and the half bush (liner) of softer metal.
• The liner has collars (flanges) at its ends which fit against the sides of the body to prevent axial movement.
• A snug or similar projection on the underside of the liner fits into a recess in the body to prevent the liner from rotating with the shaft.
• The liner is softer than the shaft, so wear occurs in the cheap, replaceable liner rather than on the shaft.
• Use: low-speed shafts carrying downward loads, for example in simple agricultural or line-shaft machinery.
• In a sectional assembly view, the body and liner are hatched in different directions, while the shaft (if shown) is not hatched.

Exam tips

• When drawing the disassembled parts, show the liner separately in two views, with its collars and snug clearly visible.
• In the assembly, check that collars of the liner lie outside the faces of the body.

Common mistakes

• Drawing the bearing with a closed top, which makes it a different bearing.
• Forgetting the device that stops the liner rotating.