Technologic outline of the practical Lesson 10 gears a gear is a toothed wheel

Screw gearing is used for converting some rotary motion into a forward motion, and for connecting shafts which are not intersecting. Spur gears are gears having straight or helical teeth cut on a cylindrical surface at an angle to the shaft axis.

Spur gearing is used to transmit power between two shafts, the axes of which are parallel. Spur gearing may be divided into three types such as: external gearing, internal gearing and rack-and-pinion gearing. Rack-and-pinion gearing serves for converting rotary motion into forward motion and is widely used in lathes. It consists of a rack-and-pinion.

A worm gear is a gear having the teeth cut at an angle to the axis of rotation of the gear body and radially in the gear face. A worm gear is driven by a worm which resembles a large screw. Worm gearing is applied for transmitting power between non-intersecting shafts which are at right angles to each other.

In practice friction gearing and toothed gearing are most widely used for transmitting power from one shaft to another and for connecting the shafts. Friction gears are used for light and medium powers in machinery which is frequently started and stopped. Their advantages are flexibility and noiselessness. The disadvantages of friction gears are the thrust on the bearings and slippage. Toothed gears are used when a constant speed is desirable and the distance between the shafts is rather small. Transmission of rotary motion is performed by means of shafts and gears or gear trains mounted on them with the help of inserted keys.

Shafts may be of different length and diameters. When rotating, the shafts transmit both the rotation and the torque. Gears replace belt-and-pulley drives where positive motion is required. Gear teeth for all types mentioned above are made in mass production by the generating process on specially designed machines. In this process, the cutter used for cutting teeth has the form of a tooth of the mating gear. One of the most important gear-cutting processes is that of hobbing. In this process the cutter used for hobbing gear teeth is made like a worm with gashes parallel to the axis to provide cutting edges on the worm. Such a cutter is called the ^uhob".

Exercise I. Use the following words and word combinations in sentences of your own:

a toothed gear, gearing, to hob, to run, to generate, rotary motion, intersecting

shafts, spur gearing, bevel gearing, worm gearing, driven shaft, angular velocity, positive motion, inserted key

Exercise II. Answer the following questions:

1. What is a gear and what is it used for? 2. Where do gears replace belt-andpulley drives? 3. What types of shafts do you know? 4. What do types of gears depend on? 5. According to what features may gears be classified? 6. What kinds of teeth cut on the gear face do you know? 7. What main types of gears can you enumerate? 8. By what processes are gear teeth produced?

Exercise III. Choose synonymical groups out of the following list:

velocity, to transmit, to intersect, smooth, to converge, to transfer, speed, to

cross, quiet, to approach

Exercise IV. Underline the suffixes and prefixes and translate into Uzbek or Russian the following groups of words: controllable, controller, incontrollable; caller, calling, recall; section, sectional;

intersect, intersection, non-intersecting

Exercise V. Translate the following sentences observing different meanings of the words in italics:

1. When the rain has stopped I noticed a worm on the lawn of our garden. 2. Worm gearing is applied to transmit power between shafts placed at right angles to each other. 3. Eccentric gears are applied for transmitting a varying angular velocity for a portion of revolution. 4. I locked the door of my flat and left the key on the shelf. 5. Gears are mounted on shafts by means of keys.

Exercise VI. Make up questions to which the italicized words are the answers:

1. Modern requirements for gears demand that they run quietly at high speeds. 2. Gear-cutting machines have been developed for the rapid mass production of similar parts. 3. The gear blank is pressed on an arbor and held between centres of the dividing head and the index tailstock. 4. Bevel gearing is used to transmit power between two shafts whose axes intersect each other. 5. Spur gearing is used to transmit power between parallel shafts.