First let me start by saying that I am terrible at complex math equations. I am not an engineer. I love designing and building mechanical things, but certain aspects of these designs are way beyond my expertise. I guess you could say I'm more of a mechanic/fabricator than engineer.
I am designing a compact tractor that will be mostly built from commonly available "universal" parts. Parts you'd be able to get from stores such as Grainger, McMaster Carr, Tractor Supply, etc.
The main concern I have with my current design is the amount of torque that will be applied to the rear axle shaft. I don't know how to calculate the breaking strength or safe working load capacity of a keyed shaft.
I understand that a keyed shaft isn't ideal for large amounts of torque but using a splined shaft is out of the question. Again my goal is to build something that is easily repairable and uses common parts. Finding or fabricating wheel hubs and other components that will fit on a splined shaft would be incredibly difficult without expensive equipment or a larger investment in getting parts made.
The axle shaft I have settled on is a 1045 carbon steel shaft with an outer diameter of 2 inches .The keyway width is 0.5 inches and the keyway depth is 0.25 inches. McMaster Carr says that the yield strength is 75,000 PSI.
This is the exact component I would use for my application if you want every dimension.
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Thanks for your help or suggestions.
Considering your concerns about torque and the limitations of using a keyed shaft, one suggestion is to reinforce the shaft by adding additional support or using a larger diameter shaft to handle the torque load. Consulting with a mechanical engineer or seeking expert advice would be beneficial in ensuring the safety and reliability of your design.