Thread casting

The threads take the shape of whatever mold or die that the (liquid or gas) material is poured into. When the material freezes into a solid, it retains the shape. Material is either heated to a liquid (or rarely a gas), or mixed with a liquid that will either dry or cure (such as plaster or cement). Alternately, the material may be forced into a mould as a powder and compressed into a solid, as with graphite.

Cast threads in metal parts may be finished by machining, or may be left in the as-cast state. (The same can be said of cast gear teeth.) Whether or not to bother with the additional expense of a machining operation depends on the application. For parts where the extra precision and surface finish is not strictly necessary (although it might be nice), the machining is forgone in order to achieve a lower cost. With sand cast parts this means a rather rough finish; but with molded plastic or die-cast metal, the threads can be very nice indeed straight from the mold or die.

Thread grinding

Thread grinding is done on cylindrical grinders using specially dressed wheels matching the shape of the threads. Although expensive, threads produced by grinding are highly accurate and have a very fine surface finish with applications such as ball screw mechanisms used for precise movement of machine components.

Technically, thread grinding is a subset of thread cutting, as grinding is a true metalcutting process. Each grain of abrasive functions as a microscopic single-point cutting edge (although of high negative rake angle), and shears a tiny chip that is analogous to what would conventionally be called a "cut" chip (turning, milling, drilling, tapping, etc.). However, among people who work in the machining fields, the term cutting is understood to refer to the macroscopic cutting operations, and grinding is mentally categorized as a "separate" process. This is why the terms are usually used in contradistinction in shop-floor practice, even though technically grinding is a subset of cutting.

Thread lapping

Rarely, thread grinding will be followed by thread lapping in order to achieve the highest precision and surface finish achievable. This is an ultra-deluxe toolroom practice, rarely employed except for the leadscrews or ballscrews of high-end machine tools

Unit 7 Gears

1. Language

Ex.1. Remember the following words and word combinations:

gear toothed wheel angular velocity ratio driving shaft driven shaft rate intersecting shaft non-coplanar curved helical gear bevel gear eccentric gear herringbone gear screw gear spur gear worm gear plane incline converge revolution strength speed width treat grind (ground, ground) accurate smooth running cone resemble frequently body forward motion connect external gearing internal gearing rack-and-pinion gearing serve lathe right angle

зубчате колесо, приладнувати зубчате колесо коефіцієнт кутової швидкості ведучий вал відомий вал швидкість , рівень перетинаючий вал некопланарний вигнутий, зігнутий вінтовe колесо (гелікоїдальне косозубе колесо) конічна передача ексцентрична зубчата передача шевронне зубчате колесо гвинтове зубчате колесо циліндричне прямозубе колесо черв’ячне колесо площина нахиляти сходитися кругове обертання, оборот сила, міць швидкість ширина обробляти шліфувати точний рівний, гладенький, плавний робота конус скидатися на часто тіло, кістяк рух уперед з’єднувати зовнішнє пристосування внутрішнє пристосування передача шестерної і зубчатою рейкою служити токарний верстат прямій кут

шестерня, зубчатое колесо, сцепляться зубчатое колесо коэффициент угловой скорости ведущий вал ведомый вал величина, скорость, степень пересекающий вал некопланарный кривой винтовое колесо ( геликоидальное косозубое колесо) коническая передача эксцентрическая зубчатая передача шевронное зубчатое колесо винтовое зубчатое колесо цилиндрическое прямозубое колесо червячное колесо плоскость наклонять сходиться круговое вращение, оборот сила, прочность скорость ширина обрабатывать шлифовать, протирать точный ровный, плавный, гладкий работа, эксплуатация конус, деталь конической формы походить, иметь сходство часто тело, корпус поступательное движение соединять внешнее зацепление внутреннее зацепление передача шестерней и зубчатой рейкой служить токарный станок прямой угол

Ex. 2. Read the following international words and guess their meaning.

Constant, inform, type, position, occupy, rotation, helical, eccentric, spiral, operate, portion, conical, convert, serve.

Ex. 3 Translate these words into English:

Займати місце, положення, обертання, служити, перетворювати, рівномірний, працювати, частина.

Ex. 4 Put these words according to the alphabet and translate:

Gear, rate, incline, width, curved, plane, smooth, speed, running, cone, resemble, frequently, accurate, revolution, converge..

Ex.5. Translate the words paying attention to the prefixes and suffixes :

To rotate – rotary – rotation – rotor

To transmit – transmission – transmitting

Power – powerful – powerless

To drive – driving – driven

To intersect – intersection – non-intersection

To occupy – occupation – occupancy

To converge – convergence – convergent

To convert – conversion - converter – converse

Ex.6. Group the words in synonymic pares :

Velocity, to transmit, to intersect, smooth, to converge, to transfer, speed, to cross, quiet, to approach

Ex.7. Find the meaning of the words worm, revolution and key in the dictionary and translate them:

1. When the train 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.

ІІ. Reading

Ex. 8. Read and translate the text A.

Text A

Gears.

A gear is a toothed wheel used to transmit rotary motion from one shaft to another. If power is transmitted between the two shafts, the angular velocity ratio of these two shafts is constant and the driving shaft and the driven shaft rotate an a uniform rate. Shafts may be parallel, intersecting and non-coplanar. Gears may be classified according to their shape and according to the position which the teeth occupy respectively to the axis of rotation. The teeth cut on the face of a gear may be curved, straight or helical.

The main types of gears are: bevel gears, eccentric gears, helical or spiral gears, herringbone gears, screw gears, spur gears and worm gears.

Bevel gearing is used to transmit power bettween two shafts, whhich lie in a common plane and whose axes intersect each other. The axes may be inclined to each other an any angle, although 90° is the most common one. The teeth of bevel gears may be either straight or spiral,

Helical or spiral gears operate on parallel shafts at high speeds, providing maximun strength of gear teeth for a given width of face. Such gears are heat-treated and then ground to accurate shape and size necessary for smooth and quiet running at high speeds.

Herringbone gears similary to helical gears also operate on parallel shafts. Herringbone gears have helical teeth radiating from the centre of the face towards the sides of the gear body.

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 : 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 con- sists 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 resemble a large screw. Worm gearing is applied for transmitting power between non-intersecting shafts which are at right angles to each other.

ІІІ . Language

Ex.9. Match word and word combinations in column A with those in column B:

A frequency spur gear 3. bevel gear curved driving shaft incline driven shaft gear intersecting shaft worm gear

B шестерня ведучий вал відомий вал перетинаючий вал вигнутий конічна передача циліндричне прямозубе колесо черв’ячне колесо нахиляти часто

Ex.10. Match words and their definitions:

A gear is Spur gear is Herringbone gear have A worm gear is Screw gearing is Bevel gearing is Helical or spiral gears

a toothed wheel used to transmit rotary motion from one shaft to another. used to transmit power between two shafts. operate on parallel shafts at high speeds. helical teeth radiating from the centre of the face towards the sides of the gear body. used for converting some rotary motion into a forward motion, and for connecting shafts which are not intersecting. used to transmit power between two shafts, the axes of which are parallel. A gear having the teeth cut at an angle to the axis of rotation of the gear body and radially in the gear face.

Ex. 11. Point out the words with –ing. Are they Participle or Gerund? Translate the sentences:

1. Testing will begin in ten minutes.

2. Testing these devices we sometimes find defects in them.

3. Connecting shafts is done automatically.

4. Connecting shafts engineers used new automatic devices.

5. Increasing the pressure we increase the force of friction.

6. Ice melting begins at 0 C.

7. Spur gears are gears having straight or helical teeth.

8. Screw gearing is used for converting some rotary motion into a forward motion.

Ex.12. Find the right ending of the sentences and translate these sentences:

1. If a power is transmitted between two shafts: … ………… .

1. they may be inclined to each other at any angle.

2. The angular velocity ratio of these two shafts is constant.

3. The driving shaft and the driven shaft rotates at a uniform rate.

1. Bevel gearing is used ………………………. .

1. to provide maximum strength of gear teeth.

2. to transmit a varying angular velocity either continuously or for a portion of revolution.

3. to transmit power between two shafts, which lie in a comment plane and whose axes intersect each other.

3. Helical or spiral gears are ………………………. .

1. used for converting some rotary motion into a forward motion.

2. heat –treated and the ground to accurate shape and size.

3. gears having strait or helical teeth.

4. Spur gearing is used ……………………………………………….. .

1. to transmit power between two shafts the axes of which are parallel.

2. for converting rotary motion into forward motion.

3. to transmit power between two shafts interacting each other.

5. Worm gearing is applied ………………… .

1. for transmitting power between non-interacting shafts which are parallel.

2. for transmitting power between non-interacting shafts at right angles to each other.

3. for connecting shafts which are not intersecting.

6. Eccentric gears are used

1. to transmit power between two shafts interesting each other.

2. to transmit power between two shafts which lie in a common plane.

3. to transmit a varying angular velocity either continuously or for a portion of revolution.

Ex. 13. Fill in the blanks using the following words:

1. forward motion; b) bevel gear; c) gear herringbone; d) screw gear; e) toothed wheel ,d) curved, e) intersecting, f) friction gear, g)worm gear, h) rack-and-pinion gearing, i) resembles.

1. A gear is a ……….. used to transmit rotary motion from one shaft to another.

2. Shaft may be parallel, …………… and non-coplanar.

3. The main types of gears are : ……………….. .

4. Similarly to helical gears …………….. also operate on parallel shafts.

5. Screw gearing is used for converting some rotary motion into ………. .

6. Spur gears are gears having straight or ……….. teeth cut on a cylindrical surface at angle to the shaft axis.

7. …………….. serves for converting rotary motion into forward motion and is widely used in lathes.

8. A worm gear is driven by a worm which …………… a large screw.