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  1. [11]
    ahmed taye3
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    تاريخ التسجيل: Oct 2008
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    Rack and pinion


    Converting rotary motion to linear motion.


    A rack and pinion mechanism is used to transform rotary motion into linear motion and visa versa. A round spur gear, the pinion, meshes with a spur gear which has teeth set in a straight line, the rack. The rack and pinion can transform rotary motion into linear motion and visa versa in three ways:

    a. Rotation of the pinion about a fixed center causes the rack to move in a straight line.
    b. Movement of the rack in a straight line causes the pinion to rotate about a fixed center;
    c. If the rack is fixed and the pinion rotates, then the pinion's center moves in a straight line taking the pinion with it.




    rack and pinion








    application










    Spur gears
    The spur gear is the last gear we will look at and the most important as far as we are concerned. We will be looking at the gear terms and how to draw the gear teeth using Unwins construction. Firstly, we will discuss the spur gear itself.

    A spur gear is one of the most important ways of transmitting a positive motion between two shafts lying parallel to each other. A gear of this class may be likened to a cylindrical blank which has a series of equally spaced grooves around its perimeter so that the projections on one blank may mesh in the grooves of the second. As the design should be such that the teeth in the respective gears are always in mesh the revolutions made by each is definite, regular and in the inverse ratio to the numbers of teeth in the respective gears. This ability of a pair of well made spur gears to give a smooth, regular, and positive drive is of the greatest importance in many engineering designs. An example of two spur gears in mesh are shown below.




    Spur gears






    Now that we have discussed the spur gear, we will look at the terms associated with spur gears

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    عندما تولد يابن ادم يؤذن فى اذنك من غير صلاة وعندما تموت يصلى عليك من اذان وكان حياتك فى الدنيا ليست الا الوقت الذى تقضيه بين الاذان والصلاة فلا تقضيها بما لا ينفع

  2. [12]
    ahmed taye3
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    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.

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    عندما تولد يابن ادم يؤذن فى اذنك من غير صلاة وعندما تموت يصلى عليك من اذان وكان حياتك فى الدنيا ليست الا الوقت الذى تقضيه بين الاذان والصلاة فلا تقضيها بما لا ينفع

  3. [13]
    ahmed taye3
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    Involute gear teeth



    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



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    عندما تولد يابن ادم يؤذن فى اذنك من غير صلاة وعندما تموت يصلى عليك من اذان وكان حياتك فى الدنيا ليست الا الوقت الذى تقضيه بين الاذان والصلاة فلا تقضيها بما لا ينفع

  4. [14]
    ahmed taye3
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    The importance of clearance



    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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    عندما تولد يابن ادم يؤذن فى اذنك من غير صلاة وعندما تموت يصلى عليك من اذان وكان حياتك فى الدنيا ليست الا الوقت الذى تقضيه بين الاذان والصلاة فلا تقضيها بما لا ينفع

  5. [15]
    ahmed taye3
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    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)


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    عندما تولد يابن ادم يؤذن فى اذنك من غير صلاة وعندما تموت يصلى عليك من اذان وكان حياتك فى الدنيا ليست الا الوقت الذى تقضيه بين الاذان والصلاة فلا تقضيها بما لا ينفع

  6. [16]
    ahmedzhelmy
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    ردا على إستفسار الأخ المهندس / شكري محمد نوري .. (البغدادي)
    والرد من الأخ المهندس / خيري محمد
    فإنني لي تعقيب على رد المهندس / خيري محمد ، حيث لا يمكن عمل ترس على المخرطة ، لأن منحنيات أسنان الترس في هذه الحالة لا تكون دقيقة ، ولو فرض وتم عمل مثل هذا الترس على المخرطة ، فإنه يحدث متاعب وصوت عال وتلف للترس المقابل له . ومن ثم فإنه يجب عمل أي ترس على الفريزة ، أو على الماكينات الخاصة لتصنيع التروس.
    مع قبولكم تحياتي ،،
    د.أحمد زكي حلمي

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  7. [17]
    الحص1
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    تاريخ التسجيل: Apr 2009
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    بارك الله في أعمالكم وجزاكم

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    قال رسول الله صلى الله عليه وسلم :
    من سئل عن علم فكتمه ألجمه الله بلجام من نار يوم القيامة

  8. [18]
    mhassanien
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    جميل جدا كمعلومات شفهية نريد أن نتطرق إلى الحسابات العلمية

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  9. [19]
    Eng_Matro
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    مشكور الله يعطيك العافية مجهود تشكر عليه

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  10. [20]
    فهد 9999
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    الموقع والمشرفين على الموقع ولا اروع

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