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I need to design a simple gearbox for homework. I figured out to locate 2 sliding spur gears on the input shaft and 2 fixed spur gears on the output shaft. I prefer to use key joints, as they are the simplest possible.

  • How can the sliding gears be constrained? Will a long key do?
  • How can the fixed gears be fixed into place? Will another design of key joint work?
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If you've got two fixed gears on the output shaft and two sliding gears on the input shaft then your gears will not be in constant mesh. Are you aware of this? This is okay if you plan to change gears while your gearbox is not transmitting torque. However during operation this is rarely the case. I think the following is a better design and is usually how automotive transmissions such as motorcycle gearboxes work anyway:

The gears on the output shaft are fully fixed axially and torsionally. The gears on the input shaft are fixed axially but are not fixed torsionally and are in constant mesh with the output shaft gears. The input shaft gears don't need a key then. In between the input shaft gears add a sliding selector gear on a key which transmits torque via dogs on the sides of the input shaft gears.

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