On the other hand the helical gearbox design would require output bearings of 7309 BE while input bearings of 7209 BE. The gearing materials were found out best to be AISI 304 while the casing ought to be created from cast iron. Cost comparison shows that spur gearbox is much cheaper especially because of the lower cost of the ring spur gear in comparison to the ring helical gear. Therefore the spur gearbox design was chosen as the optimal configuration for the current problem at hand. Summary In order to determine the best possible solution for a gearbox for an auger earth drill an extensive investigation was carried out. The investigation was begun with a literature review of the relevant means to transmit mechanical power such as belts, shafts, torque converters, mechanical couplings and gears. Given the relative advantages of gears in terms of power and speed scaling as well as the cost, it was decided to stick with gears to power an auger earth drill. The commonly used gear types which are spur and helical were dealt with in detail to understand their operational perspectives. Bevels gears were also investigated but rejected early on. Epicyclical gear trains were investigated in greater detail to achieve a functional yet compact gearbox. The three configurations possible which were star, solar and planetary were all looked at in detail. Given the gearing ratio of 5.4 to 1, the planetary gearing system was found to be most suitable and was thus used as the prime choice. It was also decided to perform a comparison between a spur planetary and a helical planetary gearbox to find out which one was better. The gear based calculations were carried out and the number of teeth was found culminating in the perfectly matching gearing ratio. The gear sizes were determined using the overall dimensions of the gearbox as a constraint. The number of planetary gears was chosen as three based on its load sharing and geometrical properties. Lubrication investigation was also carried out in detail to find out a lubricant suitable for the gearbox. Bearing selection was carried out for the gearboxes (both the spur and helical gearboxes) based on their individual requirements. The types of bearings available were investigated at length in order to discern the best possible choice. Materials for the various parts of the gearbox were also considered in detail to discern the best possible choices. This was followed by the evaluation of spur gearbox and helical gearbox design based on cost as cost was considered as an important factor. The stress analysis of the gearbox components produced satisfactory results which indicated a large operating margin for the gears involved. Images The maximum and minimum stress levels are already pretty clear in this image and other images that I have sent you. The images are always going to be the same as the gearbox under investigation is the same. The yielding strength of the material is 550 MPa and the stress levels are apparent on the picture. FOS FOS (Factor of Safety) is a measure used to indicate the relative resilience of a component to failure during normal operation. Generally the FOS is calculated by dividing the material’s own yield stress with the maximum available stress levels.