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مراجع مادة نظرية ماكينات

1-The theory of machines
Author: McKay, Robert Ferrier
Subject: Machinery
Publisher: London, E. Arnold
Possible copyright status: NOT_IN_COPYRIGHT
Language: English
Call number: nrlf_ucb:GLAD-100796701
Digitizing sponsor: MSN
Book contributor: University of California Libraries

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والكتاب اللى جاى دا مفجأه
والصوره اللى هتثبت كدا





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Applied mechanics: an elementary general introduction to the theory of structures and machines
Author: Cotterill, James H. (James Henry), 1836-1922
Subject: Mechanical engineering; Machinery; Kinematics; Gearing; Strength of materials; Hydraulics; Compressed air
Publisher: London, Macmillan and co.
Possible copyright status: NOT_IN_COPYRIGHT
Language: English
Call number: nrlf_ucb:GLAD-151191304
Digitizing sponsor: MSN
Book contributor: University of California Libraries



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The kinematics of machinery : Outlines of a theory of machines
Author: Reuleaux, Franz, 1829-1905; Kennedy, Alexander Blackie William, 1847-
Subject: Machinery, Kinematics of
Publisher: London : Macmillan and co.
Possible copyright status: NOT_IN_COPYRIGHT
Language: English
Call number: nrlf_ucb:GLAD-50468951
Digitizing sponsor: MSN
Book contributor: University of California Libraries

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Kinematics of machinery, outlines of a theory of machines
Author: Reuleaux, F. (Franz), 1829-1905; Kennedy, Alex. B. W. (Alexander Blackie William), 1847-1928
Subject: Machinery, Kinematics of
Publisher: London, Macmillan
Possible copyright status: NOT_IN_COPYRIGHT
Language: English
Call number: AEX-2883
Digitizing sponsor: MSN
Book contributor: Gerstein - University of Toronto

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The theory of machines : Part I. The principles of mechanism. Part II. Elementary mechanics of machines
Author: Angus, Robert W. (Robert William), 1873-
Subject: Machinery
Publisher: New York : McGraw-Hill
Possible copyright status: NOT_IN_COPYRIGHT
Language: English
Call number: ANB-8554
Digitizing sponsor: University of Toronto
Book contributor: Gerstein - University of Toronto


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The theory of machines. Part I. The principles of mechanism. Part II. Elementary mechanics of machines
Author: Angus, Robert William
Subject: Machinery
Publisher: New York, McGraw-Hill book company, inc.; [etc., etc.]
Possible copyright status: NOT_IN_COPYRIGHT
Language: English
Call number: nrlf_ucb:GLAD-151156290
Digitizing sponsor: MSN
Book contributor: University of California Libraries



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Ice-making machines: the theory of the action of the various forms of cold-producing or so-called ice machines
Author: Ledoux, Charles Ernest, b. 1837
Subject: Refrigeration and refrigerating machinery
Publisher: New York, D. Van Nostrand
Possible copyright status: NOT_IN_COPYRIGHT
Language: English
Call number: nrlf_ucb:GLAD-17048289
Digitizing sponsor: MSN
Book contributor: University of California Libraries



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Involute spur gear terms



The spur gear terms:
The pitch circle is the circle representing the original cylinder which transmitted motion by friction, and its diameter the pitch circle diameter.

The center distance of a pair of meshing spur gears is the sum of their pitch circle radii. One of the advantages of the involute system is that small variations in the center distance do not affect the correct the correct working of the gears.
The addendum is the radial height of a tooth above the pitch circle.

The dedendum is the radial depth below the pitch circle.

The clearance is the difference between the addendum and the dedendum.

The whole depth of a tooth is the sum of the addendum and the dedendum.

The working depth of a tooth is the maximum depth that the tooth extends into the tooth space of a mating gear. It is the sum of the addenda of the gear.

The addendum circle is that which contains the tops of the teeth and its diameter is the outside or blank diameter.

The dedendum or root circle is that which contains the bottoms of the tooth spaces and its diameter is the root diameter.

Circular tooth thickness is measured on the tooth around the pitch circle, that is, it is the length of an arc.

Circular pitch is the distance from a point on one tooth to the corresponding point on the next tooth, measured around the pitch circle.

The module is the pitch circle diameter divided by the number of teeth.

The Diametrical pitch is the number of teeth per inch of pitch circle diameter. This is a ratio.

The pitch point is the point of contact between the pitch circles of two gears in mesh.

The line of action. Contact between the teeth of meshing gears takes place along a line tangential to the two base circles. This line passes through the pitch point and is called the line of action.

The pressure angle. The angle between the line of action and the common tangent to the pitch circles at the pitch point is the pressure angle.


The tooth face is the surface of a tooth above the pitch circle, parallel to the axis of the gear.

The tooth flank is the tooth surface below the pitch circle, parallel to the axis of the gear. If any part of the flank extends inside the base circle it cannot have involute form. It may have ant other form, which does not interfere with mating teeth, and is usually a straight radial line.

For reasons of economy in production modern gear teeth are almost exclusively cut to an involute form. The involute is a curve, which is generated by rolling a straight line around a circle, where the end of the line will trace an involute. The figure below shows the construction of an involute. To use this method to draw a gear profile would be very time consuming, so we will use an approximation called Unwins construction.





Involute






If two meshing gear were manufactured with square teeth instead of being cut to an involute form, the gears would not be able to rotate in mesh. The diagram below shows two such gears. note how the gears are locked together.
square teeth



The importance of clearance

To construct a gear profile using Unwins construction


Because the drawing contains a large amount of construction lines, the gear profile is drawn in three steps. Before you begin to draw the gear profile, you must obtain all the information needed using the given data and above formulas.
To view these three easy steps, simply click on the text below.



Step 1 (animation)




Step 2 (animation)


Step 3 (animation)



Clearance is the distance from the tip of a tooth to the circle passing through the bottom of the tooth space with the gears in mesh and measuring radially.
The correct clearance is vital to the motion of gears. To view two spur gears rotating in mesh and the necessity for clearance, simply click on the text below.

Rotating spur gears in mesh animation



close up of spur gears in mesh animation
Proportions and relations of standard involute spur gear teeth



The following formulas are required to calculate the dimensions needed to draw a tooth of a spur gear.


Addendum = module,

Dedendum = addendum + clearance,

Clearance = 0.25 x module,

Module (m) = pitch circle diameter (PCD) / number of teeth,

So, PCD = m x T,

Circular pitch (P) = pi (3.14) x m,

Circular tooth thickness = pi / 2,

Base circle diameter (BCD) = (PCD) x cos. Y ,

Pressure angle ( Y ) = 14.5 degrees or 20 degrees , the British standard recommendation is 20 degrees.
This value reduces the possibility of interference and gives the tooth a wider root.




Now that we know what spur gears are used for, what they look like, and how to calculate the information required to draw them, we can turn to the next page to see how each step is drawn.
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Gear types

Bevel gears

These gears have teeth cut on a cone instead of a cylinder blank. They are used in pairs to transmit rotary motion and torque where the bevel gear shafts are at right angles (90 degrees) to each other. An example of two bevel gears are shown below.





Bevel gears










Crossed helical gears

These gears also transmit rotary motion and torque through a right angle. The teeth of a helical gear are inclined at an angle to the axis of rotation of the gear.
The diagram below shows how the axis of rotation of two helical gears are crossed at right angles. Helical gears are smoother running than spur gears and are more suitable for rotation at high velocities. An example of two crossed helical gears are shown below.




Crossed helical gears










Worm and worm wheel

A gear which has one tooth is called a worm. The tooth is in the form of a screw thread. A worm wheel meshes with the worm. The worm wheel is a helical gear with teeth inclined so that they can engage with the thread – like worm. Like the crossed helical gears, the worm and worm wheel transmit torque and rotary motion through a right angle. The worm always drives the worm wheel and never the other way round. The mechanism locks if the worm wheel tries to drive the worm. Worm mechanisms are very quiet running. An example of a worm and worm wheel is shown on the right hand side below. An application of the worm and worm wheel used to open lock gates is shown on the left hand side below.





Worm and worm wheel






application










The helical gear
This gear is used for applications that require very quiet and smooth running, at high rotational velocities.
Parallel helical gears have their teeth inclined at a small angle to their axis of rotation. Each tooth is part of a spiral or helix. The helical gears shown below have splines cut in their center holes. The gears can move along a splined (grooved) shaft, although they rotate with the shaft. An example of a helical gear is shown below.
Double helical gears give an efficient transfer of torque and smooth motion at very high rotational velocities. An example of a double helical gear is shown below.




Single helical gear


Double helical gear









Spiral bevel gears

When it is necessary to transmit quietly and smoothly a large torque through a right angle at high velocities, spiral bevel gears can be used. Spiral bevel gears have teeth cut in a helix spiral form on the surface of a cone. They are quieter running than straight bevel gears and have a longer life. Spiral bevel gears are used in motorcar rear axle gearboxes. An example of spiral bevel gears are shown below.





Spiral bevel gears












Face cut gears
It is possible to cut gear teeth on the face of a gear wheel. Also, gear teeth can be cut on the inside of a gear ring an example of which is shown in the top figure below. Internal gears have better load carrying capacity than external spur gears. They are safer in use because the teeth are guarded. An example of an external face cut gear is shown below.



Internal face cut gear





External face cut gear