Designing a customized Gearbox

Project Info


We were requested by a client to design a gearbox for a special purpose. The client wanted to roll a metal sheet with a thickness about 8 mm. According to the client’s requirement, a hydraulic motor was to drive the gearbox and increase its output torque.


While it was initially perceived that this project would be an ordinary design, the client requested us to design the body of the gearbox in a way that he could make it in his workshop that did not have any molding tools.

In this scenario, the concentrically bearings brackets and the distance between the gears was a challenging subject. We were also faced with another problem and it was the problem of gears’ lubrication and sealing the input and output shafts.


In order to make the design in a way that the client could make it without using any molding equipment, we designed the body of the gearbox in 6 parts with accurate dimensions. Based on these designs, the   client used a very simple method to make the actual gear by just using welding and drilling tools.

He just made a print out of the drawings in a one to one scale and then cut the metal sheet for each part. The metal was an ordinary ST36 iron.
The sealing of the gearbox caps was provided by using an O-ring washer and after all the gearbox worked perfectly.

The technical specifications of the design and the gears included the followings:

Transfer rate = 2:1

  • The number of small gear teeth (P)=19
  • Pinion pitch circle diameter =114 mm
  • Addendum diameter =130 mm
  • Dedendum diameter=102 mm


  • The number of big gear teeth (G)=38
  • Gear pitch circle diameter=228
  • Addendum diameter =244mm
  • Dedendum diameter=216


  • Bearings type: Roller bearing NACHI
  • The big one is: NNU4936 basic dynamic load rating=480KN
  • The 4 of them are: NN3010 basic dynamic load rating=53KN

As requested by the client, the final solution featured all the given requirements and could be made just by using welding and drilling tools. The client made the designed gearbox and used it with a hydraulic motor. The final result was quite successful and he managed to use the final equipment was strong enough to roll a metal sheet with a thickness of 8 mm.

J. Clark
April 21, 2018
Mechanical Engineering