Mechanical Engineering - Machine Design - Discussion


Which of the following statement is correct for gears?

[A]. The addendum is less than dedendum
[B]. The pitch circle diameter is equal to the product of module and number of teeth
[C]. The pitch circle is always greater than the base circle
[D]. all of the above

Answer: Option D


No answer description available for this question.

Rajam Solanki said: (May 9, 2014)  
This is wrong because addendum circle is always greater than dedendum circle.

M.Tariq said: (Mar 14, 2015)  
The first answer (A) is incorrect it should be reversed to be "The dedendum is less than addendum".

Rathi said: (Mar 15, 2015)  
Why dedendum is larger than addendum?

Meshing of mating teeth should occur on the involute portion of teeth. The teeth have involute profile from the base circles to addendum circles. If there is inaccuracy in manufacturing of gears, then the tip of tooth of one gear (always lies on its addendum circle) will dig the bottom portion of mating gear that results in interference. To avoid this bottom land of gears are lowered such that it lies on the periphery of the dedendum circle. The dedendum circle is made smaller than the base circle and also lies below the pitch circle at distance, 'b'. Addendum circle lies at distance 'a', beyond the pitch circle, such that b > a.

Chandan said: (Dec 25, 2015)  
Guys the question said addendum not circle!

Gaurav said: (Jun 22, 2016)  
Very well said @Chandan.

Ravindra said: (Jul 1, 2016)  
Addendum is the distance from pitch circle to the teeth head, so it must be less than dedendum.

Alok said: (Jul 21, 2016)  
Please, give an explanation about option B.

Glorie said: (Jul 5, 2017)  
Please, is it must for the pitch circle diameter to be greater than the base circle diameter.

Ravi Gupta said: (Aug 2, 2017)  
Pitch circle diameter is the product of module and not no of teeth.

Raghuprasad said: (Sep 5, 2017)  
Module m: Pitch diameter divided by number of teeth: m= D/T.
Circular pitch p: The width of a tooth and a space, measured on the pitch circle. Cp= π*D/T.
Diametral pitch P: The number of teeth of a gear per inch of its pitch diameter. Dp = T/D.

Ani said: (Nov 26, 2017)  
Dedendum = 1.157*addendum.
Addendum = radial distance from pitch circle to top of tooth.
Dedendum = radial distance from pitch circle to base of the tooth.

Sahid Parvez said: (Dec 16, 2017)  
Addendum- it is the radial height of a tooth above the pitch circle.its standard value is one module.

Dedendum- it is the radial depth of a tooth below the pitch circle. It's standard value is 1.157m.

Rishi said: (Feb 16, 2018)  
Well Said @Sahid Parvez.

(It's correct Tooth Proportions).

Mangesh said: (Mar 11, 2018)  
The correct Answer is C.

Saif Ul Islam said: (Apr 13, 2018)  
Addendum is 1m.

Dedendum is addendum+clearance =1m + 0.157m=1.157m.
i.e 0.157 larger than addendum.

Akhilesh Tiwari said: (Oct 26, 2018)  
Dedendum greater then addendum is the Right answer.

Dedendum= addendum + clearance so dedendum always greater then addendum.

Sid said: (Apr 16, 2019)  
Can anyone explain about option B?

Vns700 said: (Apr 21, 2019)  
The formula of module is diameter/no of teeth.

Hence option B.

Aditya Raj said: (Oct 29, 2019)  
Given the answer is right guys.

Muhammad Saad said: (Jul 17, 2020)  

It is written pitch circle diameter =module * a number of teeth.

As we know that;
Module=pitch circle dia/no.of teeth.
So, option B is also correct.

Atanu said: (Apr 1, 2021)  
Addendum > Dedendum.

Pitch circle = [(πD)/T] .
D= Pitch cycle dia, T= Number of teeth.

Dedendum dia is a base circle dia .
so, Base circle < Pitch circle is always.

That's why a correct answer is an option [C].

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