International Journal of Advance Engineering and Research Development Volume 1,Issue 12, December -2014 @IJAERD-2014, All rights Reserved 205 Scientific Journal of Impact Factor(SJIF): 3.134 e-ISSN(O): 2348-4470 p-ISSN(P): 2348-6406 EFFECT OF PRESSURE ANGLE ON CONTACT RATIO OF ASYMMETRIC INVOLUTE SPUR GEAR TEETH P A Vaghela 1 , S P Dayal 2 1 Mechanical Engineering Department, R C Technical Institute, Ahmedabad, Gujarat, India Email id:pavaghela@yahoo.co.in 2 Mechanical Engineering Department, Government Polytechnic, Vadnagar, Gujarat, India Email id: swatidayal@rediffmail.com Abstract — The main objective of this paper is to show effect of pressure angle on contact ratio of asymmetric spur gear teeth. Analytic calculation has been done with illustration and conclusion made on it. A programme has been developed in SciLab software to obtain contact ratio of Asymmetric Spur Gear tooth. Step by step producer has been describing to obtain contact ratio of Asymmetric Spur Gear tooth. Keywords- Asymmetric Spur Gear, contact ratio I. INTRODUCTION Asymmetric Spur Gear tooth means both side of gear profile are with different pressure angle as shown in fig.1. Fig. 1 asymmetric involute spur gear tooth. Pressure angle on Drive side involute profile is higher or lower than coast side involute profile as requirement shown in fig.1. As per definition of involute function it depend on pressure angle and mathematical description are given below [3].      tan inv (1) Where,  = pressure angle Generally pressure angle on coast side profile kept constant and it is 200 while pressure angle on drive side profile increases, higher pressure angle on drive side reduce bending stress at critical section of gear tooth [1,2] which is beneficial. But contact ratio is also depending on pressure angle as per equation 2. So, study of how different pressure angle affect on contact ratio is necessary which is done in this paper with illustration. II. CONTACT RATIO Contact ratio is a measure of the average number of teeth in contact during the period in which a tooth comes and goes out of contact with the mating gear [5]. Contact Ratio is the ratio of the arc of action to the circular pitch [5].