Shafts. Types of Shafts and Their Properties

We’re here with shafts and journals, one of the machine elements topics. In this article we’ll look at topics such as the types of shafts and journals, what a journal is, the difference between a journal and a shaft, and shaft calculations covering deflection and strength, shaft diameter calculation, and calculating the load a journal can carry.

SHAFTS

These are machine elements that are circular in cross-section and long in length, and that perform rotary motion. They either rotate by means of the elements mounted on them, or they generate the initial rotary motion themselves and transmit motion and force to other elements.

Properties of Shafts

In general, shafts do their job by having elements such as pulleys, gears, flywheels, cams, etc. mounted on them. The elements mounted on them are attached by means of keys, pins, bolts, and nuts. Keyways and pin holes are cut into the sections where these elements are mounted, so the elements rotate together with the shaft.

Because of the weight of the elements mounted on them and the turning moments they carry, shafts are subjected to bending. In poorly aligned bearings, they also wear down the bearing.

They’re subjected to bending because of the weight of the parts mounted on them and the tension/pulling forces from belts. Shafts are generally made from mild steel with a tensile strength of 42-50 kg/mm². To make their outer surfaces very hard and wear-resistant, they undergo case hardening or nitriding.

Types of Shafts

a. Plain shafts  b. Flexible shafts  c. Hollow shafts  d. Crankshafts  e. Splined shafts

Plain Shafts (Line/Transmission Shafts)

Plain shafts, also called transmission shafts, are shaped in every dimension, diameter, and length to fit the requirements and form of the job. They’re assembled by supporting them at their two ends. In general their length is short. Longer ones, since bending would occur, need to be supported at the middle as well.

Flexible Shafts

These are shafts used in applications where they need to change shape while operating. They’re used, for example, in shafts for sharpening tools, flexible-shaft grinder spindles, dental drills used in dentistry, protecting electrical cables, and similar applications.

Hollow Shafts

These are shafts with a bored-out center, used as spindles in work-holding machines. By having their center bored out, these shafts lose an average of 10% of their strength. Their load-bearing capacity is weakened.

Crankshafts

In engines, these are the shafts that convert the pistons’ linear motion into rotary motion. Since crankshafts need to run in balance, they need to be machined precisely.

Splined Shafts

TS 147/19 Shafts made generally with 6 or 8 splines are used in heavily loaded gearboxes and motor vehicles. Splines on shafts are cut on a milling machine either using a dividing head setup, or by the hobbing method using a slotting cutter. Splined shafts assist the elements mounted on them with axial sliding.

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