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  • Gear & Shaft hole relation

    hiten

    Member

    Updated: Oct 26, 2024
    Views: 1.1K
    Hi,
    Whenever we design a Gear pair in Machine Design [referring to books like VB BHandari or Khurmi Gupta], I believe that the Gear is assumed to be solid with no shaft hole.

    However, if a shaft hole and a keyway were to be machined, the strength of the gear would obviously reduce as material would've been reduced.

    Can anybody please tell me what relation would there be between the volume of the Gear and its strengt.

    Say I've need to machine a Gear having mean diameter D = 140 mm with a hole in it for accomodating a shaft of diameter d = 48 mm.

    If by normal calculation [ie selecting the module of the gear and the diameter] I find that the material required will have an UTS of 900 MPa, then by how much greater will the UTS increase if the 48 mm dia hole needs to be machined in the Gear so that it can sustain the applied Torque

    Would greatly appreciate help in this matter and also some relaible reference [online or Books] explainging the same

    TIA 😀
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  • suhasvd

    Member • Apr 18, 2010

    Hi,

    I believe there is no direct relation between the volume of the gear and strength of gear. Whereas the stresses causing due to torsion ( incurred due to torque application) will cause shear failure. In this case you need to find the shear stress and calculate the cross-section required at the each point of radius.(Note: for optimized gear thickness of the gear can be change depends on the radius and torque load ).

    If you are considering the hole, and the shear stresses in the hole are below the allowable shear stress, you need not to give any reinforcement. Else you need to increase the local thickness to meet the allowable stress requirement.

    Make sure that stresses calculated should be less than the UTS.. adjust thickness of the gear accordingly.

    Suahs
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