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Shaft size

  1. Dec 14, 2015 #1
    hello i have a torque of 100 Nm. how to calculate the shaft size?
  2. jcsd
  3. Dec 14, 2015 #2
    I would love to help you but you need to either provide information on how much force you are applying or how long the shaft is, with the latter assumed to be the question. It may also help to give some context, what scenario is this shaft and torque in?
  4. Dec 15, 2015 #3
    I have a rotating shaft wiht a disc on top of it .The moment of inertia of the system is 185 kgm2.i would like the system to attain a speed of 35 deg/sec with an acceleration of 10 deg/sec2. so the torque comes out to be 101.5 Nm. Now what should be the shaft diameter?
  5. Dec 15, 2015 #4
    You need to know the yield stress of material of your shaft. Then you insert this value to equation for maximum sheer stress (assuming you have pure torsion). This should give you the value of diameter which will cause your shaft to get on the edge of yielding. Used diameter should be bigger than this. How much bigger depends on requested safety factor.

    By the way, if I remember correctly, relation between torque and angular acceleration is given as T=J*α (T - torque, J - moment of inertia, α - angular acceleration in rad/sec2).
    With your values, it gives T about 32 Nm. Or am I missing something ?
  6. Dec 15, 2015 #5


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  7. Dec 15, 2015 #6
    A couple of questions here:
    If you know the moment of inertia of the whole system, doesn't that mean that you have figured out the dimensions of the system? If I am given those information, I would use the formula here:
    to figure out what combination of dimensions will have that value.

    On the angular velocity and angular acceleration part, I am not sure what is the unknown here, if you know the final velocity and acceleration, what you can find is time of acceleration, in this case it would take 3.5seconds.
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