History of the Lathe

All lathes by their very nature rely on a revolving work piece. To capture and impart this motion, to devise and create the required force has challenged mans ingenuity back into pre-history. Man has been using the momentum provided by a spinning weight for tens of thousands of years in the form of drop spindles for spinning wool. The potter's revolving 'wheel was almost certainly the first machine used by our ancestors. It maybe that the reciprocating bow drill and pump drill in it's many forms was the first mechanical hand tool.

Small lathes driven by a hand held bow probably provided the earliest form of turning, particularly of small items, not just of wood but Ivory, bone, amber and precious metals. Very fine gold Celtic jewelry has been shown to have been worked on the bow lathe. Bow Lathes also figure in early engineering, especially in clock and watch making.

It is almost certain that the earliest lathes also encompassed reciprocation with the power provided either by the workman himself or with the aid of another individual. The earliest illustration of a lathe is from a well known Egyptian wall relief carved in stone in the tomb of Petosiris dated some 300 BC. As with many Middle Eastern and eastern lathes of this type it was operated at ground level, in this case by two men. Due to standard Egyptian artistic convention each element of the lathe is depicted in the most comprehendible manner for the observer. This results in a misleading depiction as it appears to show a vertical lathe when in fact what is intended is a horizontal strap lathe. One man provides the power by pulling backwards and forwards on a cord or leather strap wrapped around the work piece while the turner sits opposite with his chisel on the tool rest.

3. Listen to the text once again and answer the following questions:

1. Why do all lathes rely on a revolving work piece?

2. What was the first machine used by our ancestors?

3. What was the first mechanical hand tool?

4. What was figure in early engineering, especially in clock watch making?

5. When did the earliest illustration of a lathe carve in stone?

V. Communicative skills.

Using the text “Milling machine” make a short report “What is the purpose of milling machines”?

Unit 10 Topic: Machine parts. Fastening

1. Pre – reading tasks.

a) You will read a text about the main machine elements. Do you know a number of separate parts of any machine?

b) Read and memorize the following words and word-combinations in their specialized meanings.

1. require – вимагати

2. timber – лісоматеріали

3. comprise – заключать в собі

4. refer – відсилати

5. rivet – заклепка, клепати

6. piston – поршень

7. rod – стержень

8. deteriorate – погіршуватись

9. strength – міцність сила

10. stiffness – густина

11. resist – опір, не сприймання

12. safety – безпека, зберігання

13. compliance – безпека, зберігання

14. prime mover – тягач

2. Read and translate the following text into Ukrainian. Basic requirements for Machines and Machine Elements

Mechanical engineering is the backbone of heavy industry and plays a prominent role in the economy of a country.

The technical level of other branches of the national economy such as light, food, timber and building industries, transport and agriculture depends, to a great measure, upon the advancements in engineering.

A machine is a combination of a number of separate parts designed to perform work related to the process of conversion of energy or the process of production. Machines are classified as prime movers that convert some form of energy into mechanical work; converting machines that transform mechanical work into another form of energy transport machines that convert the mechanical work done by the engine or motor into the mechanical work involved in moving certain masses; and, finally, production machines designed for performing certain technological processes, i.e., to modify the properties, shape, size or state of the material processed.

All machines are comprised of parts and units. An element is a separate part of a machine either integral or consisting of several pieces rigidly jointed together by welding, riveting, etc.

Machine elements can be classified in two groups:

General purpose elements common to machines of various types and applications (e.g., bolts, nuts, axles, shafts, bearings).

Special-purpose elements employed only with a certain group or type of machines (e.g., pistons, connecting rods, cardan shafts).

Hence, the following are the basic requirements of the elements of any machine:

Strength. The machine element must not collapse or be permanently deformed by the forces applied within a specified service life.

Stiffness. Elastic deformation of the machine element under the effect of the forces applied should not exceed certain preset values.

In determining the serviceability of a part, strength and stiffness are the main criteria and should, therefore, be calculated the designing stage.

Wear resistance. Wear of a machine element within the specified service life should

not impair its mating with other elements, not should it result in undue reduction of

strength. The wear of friction parts can in some cases be reduced by normal lubrication

and in others, by increasing the strength and hardness of the working surfaces, or by increasing the contact surface.