Gear Design | Spur Gears


Introduction to design of spur gears In this video we will learn how to design spur gears. Here we will learn the design of spur gears for its mechanical strength, for dynamic loading conditions, and finally for surface durability. We will meet all the design requirements conforming to the AGMA standard. In a really simplified manner. So, let’s get into it. Before starting the design will have the following design requirements. or design inputs. Here the gear should be able to transform an angular velocity to another angular velocity RPM1 to RPM2 and it should transmit a specified
amount of power also there will be some space constraints so this design should be able to meet
that also And most of the time material of design is an input to the designer So using this design data, the designer has to find out The following gear parameters
such as Number of teeth on both the gears Pitch circle diameter addendum and dedundum face width and tooth thickness so these are the outputs we are expecting from a gear design so lets see how we can deduce values from this input data We will start the design by considering the space limitation constraint the designer cant design a gear of any size if he does so there can be two problems. First, the gear may not be economical at all Second, the gear may not get fit into the space which is supposed to get fit so there is a space constraint when designing the gears Assume the desired gear should go within the desired area. Something like this. So the designer cannot xxxx say if some this diameters of these two gears they should less than the allowed width, say eigthy percent of the allowed witdth so this is one equation And we also know the speed ratio of the gear so we can write another equation like this Next step, determination of number of teeth on each gear first step, you have to assume a number of teeth t one for small gear here, I should say something to you: desing is an open ended problem there can be many solutions for a single problem and all of them can be right according to your first assumption the design may change but you have to star like this if you know t one you can find out number of teeth on second gear using this relation and this .. diametal pitch Now we got the number of teeth on both of gears but still there is a small issue it has to be checked for The issue of interference Interference means if your gear has got profile below base circle that won’t be involute shape so if this portion of the gear comes in contact with the meshing gear it can cause material erosion and huge problems of noise but you could avoid this interference if following conditions are satisfied if number of teeth are more ….greater than this value then there won’t be any interference So for check for this if this conditions is true evertything is perfect you’ve got number of teeth in both gears but if this condition is wrong then you have increase value of t1 and have to redo this calculation again and here aw means addendum value and xxxx per xxx of gear and usually sin of phi takes 20 degres in that case you can take addedum of one module and deddendum one point two module and module is defined like this Next, design for strength of gear or your gear should able to withstand the force acting on the gear here, if there is a force acting on the gear the gears has two components one: tangential and one radial the tangential ….induce a bending stress over the xxx of the gear and if the maximum value is bending stress induced over here is more than the allowed stress limit the gear will fail you can avoid this can of failures by designing with help of an equation call Lewis bending equation before preceding to the Lewis bending equation we should determine tangential force first you know tangential force at gear multiplied by xx velocity And you know the power transmitted so you can solve for Ft Now, according to Lewis bending equation maximum bending stress induced over here will be this

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