Machine parts and machine drawingsBearingsFriction is greatly reduced in moving parts by using bearings.

In industries bearings are used to help in smooth running of shafts.

Bearing is a part of a machine which support another part that turns round a wheel.

Bearing is a support and guide for rotating, oscillating, or sliding shaft , pivot or wheel.

Two types of bearings according to type of motion are plain bearings and antifriction bearings or roller bearings.

Plain bearings support sliding, radial and thrust loads and linear motions.

Plain bearings are classified as

Plain Journal Bearings: These support radial loads at right angles to the shaft axis.

Spherical Bearings: These are used where the loads are not aligned and are radial.

Thrust Bearings: These bearings support axial and radial loads.

Linear Bearings: These bearings only help in linear motion.

5. Pivot Bearings or Foot Step Bearings: These bearings are used where the thrust is only axial.Anti-friction or roller bearings are classified as

Needle bearings

Ball bearings and

Roller bearings

The bearings mentioned above can be rearranged according to the loading conditions as:

1. Journal Bearings: In this bearing the bearing pressure is perpendicular to the axis of the shaft.2. Thrust Bearing or Collar Bearing: In this bearing the pressure is parallel to the axis of the shaft.3. Pivot Bearing: In this bearing the bearing pressure is parallel to the axis of the shaft and the end of the shaft, rests on the bearing surface. 4. Linear Bearings 5. Spherical Bearings.Journal bearing forms the sleeve around the shaft and supports a shaft at right angles to the axis of the bearing.

Examples of journal bearing are

Open bearing

Bushed bearing

Plummer block or pedestal bearing

Pivot bearing or footstep bearing

Bushed bearing is a journal bearing in which a bush made of soft material such as brass, bronze or gun metal is used.

It is useful for higher loads at medium speed.

The brasses(bushes) are prevented from rotating or sliding by the use of grub screw or dowel-pin inserted half inside the bush and half in the body of the bearing.

The bushed bearing is generally placed near the ends of the shaft, because in this the shaft can be inserted and wise only.

The sole is recessed up to 3mm leaving a standing material all around, known as padding which helps in the stability and reduces the machining area.

Open bearing is useful for linear and zig zag shafts and shafts rotating at low speeds.

The plummer block is also known as pedestal bearing

This bearing is useful for long shafts requiring intermediate supports and are preferred over ordinary bushed bearings.

It was named after its inventor PLUMMER.

It is used for shafts rotating at high speeds and hence needs frequent replacement of brasses due to wear and tear.

The cap in the bearing rests on the upper brass , fits inside the body with its body cap at its sides but does not sit on it.

Footstep bearing is used for supporting the lower end of the vertical shaft.

The drawback of this bearing is that there is no proper lubrication, thus unequal wear and tear is there in the bottom of the round disc.

Rod jointsA cotter is a flat rectangular cross section wedge-shaped piece or bar of mild steel block which is uniform in thickness but tapering in width on one side in general

It is used to connect rigidly two rods, whose axes are collinear and which transmit motion in th axial direction(tensile or compressive force) without rotation.

Thickness of cotter(t)=0.3D

Length of cotter(l)=3.5D to 4D, where the average dimension of the cotter is (d)=1.3D

The cotter joint is a temporary fastening, which allows the assembly and disassembly of a unit without damaging the fastened elements of the connecting components.

Steel is the common element used for this application

Applications of cotter joint are fastening of piston rods and cross heads in steam engines, yokes in rods, tool fixtures and for services of similar kinds.

The joint is useful in the following conditions

(i) To connect a rod directly with a machine, so as to transmit a force to the machine through the rod or vice- versa.(ii) When it is desired to increase the length of the rod.(iii) To connect two rods rigidly in the direction of their length.

There are three cotter joints for connecting circular rods

Sleeve and cotter joint

Socket and spigot joint and

Knuckle joint

For joining square or rectangular rods gib and cotter joint is used.

Sleeve and cotter joint is used to connect two round rods or sometimes to connect two pipes /tubes.

The ends of the two rods to be joined are chamfered to avoid burring and easy insertion in the hollow steel sleeve

When sleeve and rods are subjected to axial tensile force then the cotter is subjected to shearing force.

These joints are used for light transmission of axial loads.