# Design procedure of gear box for automobile and machine tools

This article gives the complete design process of a Gear Box. This includes a step-by-step guide to the design of each component of a Gear Box which is a part of any machine tool or automobile for speed and torque change purposes.

## Importance of Gear Box

What is a Gearbox? A Gear Box is a speed variable device that changes the speed of the power transmission devices according to the requirements of torque. We normally use various power transmission devices like automobiles, lathe machines, drilling machines, milling machines, or any other machine tools which require power at different torque or speed as per the will of the operator or based on the operation performed. High torque operations require low speed and vice verse. E.g. when we drive the vehicle/automobile on a steeper road, we lower the speed to have increased torque. Power and torque are directly proportional but speed and torque are inversely proportional according to the formula:

Power transmitted = 2 x PI(=3.14159) x Speed x Torque/60 Watt

Different operations require different torque or power. Thus, we can fulfill the requirements by changing the speed. This speed variation can be done by using different gears having different teeth cut on them. These gears are fitted on various shafts at the proper distance to have perfect mesh in between the two gears. In the case of lathes, and milling machines the speeds are fixed by the required cutting feed and/or cutting speed for a range of materials. Low-strength materials can be cut at higher speed and high-strength materials required higher torques so the speed needed is very low compared to that of low-strength materials. Also in the case of automobiles maximum and minimum speeds of the vehicle determines the size of the gearbox.

Those students who are in final year mechanical engineering, can take Gear Box design as their final year project. You can refer to various other options for final year project topics here.

## Design procedure for Gear Box

One has to follow a step-by-step method or procedure to complete a design task. Follow this procedure to have an idea about how to design a complete Gear Box with each component's design.

1. Determine the maximum and minimum speeds of the output shaft. This will determine the complete speed ratio. Calculate the number of steps or speed reduction stages for this range. This depends on the application as well as space optimization. Higher reduction stages require more space because of more number of gears and shafts requirements. This can be a limitation for automobiles to keep car bodies less bulky.

2. Select the type of speed reducer or gearbox based on the power transmission requirements, gear ratio, positions of the axis, and space available for the speed reducer. Also, make sure that for low gear ratio requires single-speed reduction. One can select worm gears for silent operation and bevel gears for intersecting axis.

3. Determine the progression ratio which is the ratio of maximum speed and minimum speed of the output shaft of the Gear Box. The nearest progression ratio should be a standard one and is taken either from the R 20 or R 40 series. You can refer to the design data book for this task.

4. Draw the structural diagram and kinematic arrangement indicating various arrangement possibilities during speed reduction or increment.

5. Select materials for gears so that gear should sustain the operating conditions and operating load. Normally cast iron is chosen for housing and cast steel or other alloy can be selected as per the load requirements.

6. Note down the maximum power output in Horse Power (H.P) or transmission power and revolution per minute of short i.e. rpm of each shaft.

7. Determine the center distance between the driven and driver shaft based on the surface compressive stress.

8. Determine the module of gear by beam strength as well as fix the number of teeth required.

9. Calculate the diameter of the shafts by torque requirements and bending moment considerations.

10. Calculate the key size, shape, or type of transmission keys for each gear.

11. Select appropriate fit and tolerance for mating parts like shaft and gear.

12. Select bearings types based on the loading and operating conditions. The bearing can be selected based on load and speed. Also, make sure to include consideration of maximum speed and expected life of gears and gearboxes. Normally ball bearings and roller bearings are used for the small size of the gearbox because they have lower thrust requirements due to low-speed reduction.

13. Make the shaft step or provide a collar to prevent axial displacement of bearing and gear.

14. Provide suitable clearance between gears and walls of the housing of a gearbox and based on these considerations design the casing/housing of the gearbox.

15. Complete the design of the casing. One should Provide fins if necessary to have increased heat transfer by convection and conduction. Put inspection hole/manhole as well as a drain hole to drain lubricating oil. Also, provide an oil level indicator to have the proper amount of oil during operation, if not put, this will lead to failure of gear and shaft due to overheating or due to frictional failure. Provide transportation hooks for transporting the gearbox from one place to another or during installation and maintenance. Also, design the gear changing lever accordingly.

16. Draw neat and clean working drawings in suitable software like AutoCAD, Pro-Engineer, etc., indicating required details during manufacturing or assembly.

17. One can also perform finite element analysis of the complete Gear Box after it completely designed.

Author: Muhammedaneez21 Nov 2012 Member Level: Gold   Points : 4

Nowadays all have their own vehicles. Most of them are aware about the common parts of their vehicle. But they are not aware of the most important part of the vehicles which is gear box. Gear box plays a great role in the manufacturing of vehicles. In appropriate changing of gears will affect the engine of the vehicle and it will also reduce the mileage of the vehicle. So it is important to know about the gear box of the vehicle and its function. This article will be helpful for those studyies. This will be a helpful topic for mechanical students for their projects, assignments and also for improving their knowledge.

Author: Dr. Paresh Gujarati21 Nov 2012 Member Level: Gold   Points : 3

Yes, Muhammedaneez, you are right. This project deals with complete Design subject that is covered in entire Mechanical Engineering during bachelors. This project includes design of each principal element like shaft, key, gears, housing, hook as well as material selection. This is just a reference how you can cover complete Machine Design subject during your project work in final year.

Guest Author: valiya shailesh21 Apr 2014

I am p.g student my project based on gear box so please send a report of gear box design.

Guest Author: Ashwini02 Nov 2014

Please send me the report.

Guest Author: Samuel14 May 2015

It is very nice article.

Guest Author: Alffy07 Jun 2015

Would you please send the formulas to calculate in the gearbox design.....

Guest Author: mer13 Feb 2016

Can I get a report of this for reference? It is urgent.

Guest Author: firdaus26 May 2016

Is there any existing sample gearbox calculation reports as a reference?

Guest Author: aakash28 Sep 2016

Please give any example with all calculations so that it will be more easy to understand. Nice article.

Guest Author: Cristina11 Mar 2019

Can you please send me also the report? I'm a student, working on a project like this. Also, can you tell me how I can have a reverse motion to this kinetic arrangement?

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