# Shaft Torque

1. Aug 4, 2009

I have a stainless steel shaft that is Ø140mm x 936mm long.

I need to calculate what the maximum torque is that I can apply to this shaft. I have looked around for formulas and have just got myself confused. Could someone tell me what the formula is that i need to work this out.

2. Aug 4, 2009

### CFDFEAGURU

What is the maximum torsional stress allowed for the shaft material? You will need this for the equation. Also, you need to calculate the polar moment of inertia, J, of the shaft and calculate the shafts section modulus, Z. The equation for Z is Z=J/c and c=outer diameter/2.

Last edited: Aug 4, 2009
3. Aug 4, 2009

The figure i have for the material is 77,000N/mm^2

4. Aug 4, 2009

### CFDFEAGURU

Ok now you can run the equation. Do you know how to calculate J?

5. Aug 4, 2009

Sorry no i dont know how to calculate J.

6. Aug 4, 2009

### CFDFEAGURU

Do you have a book on strenght of materials?

7. Aug 4, 2009

I dont have a strength of material book.

Could yoou tell me the equations that i need.

Like T = ? ? ? ? ?

and

J = ? ? ? ? ?

8. Aug 4, 2009

### CFDFEAGURU

Well,

T = Z*(allowable stress) where Z = J/c

J = PI/2(r^4) if the shaft is solid. Is the shaft solid?

r = c = Outside Diameter/2

Think you can handle the rest?

Last edited: Aug 4, 2009
9. Aug 4, 2009

### CFDFEAGURU

Lastly, be sure to check and make sure all of the units are correct. You should end up with N-mm

Thanks

10. Aug 5, 2009

I have calculated the torque using the formulas given and i get 3.5E-5 Nmm of torque that a Ø140mm shaft can transmit when material allowable stress is 77,000N/mm^2.

I think somewhere i have miscaculated, i have checked a couple of times and got the same result.

O/D = 140mm
R = 70mm
Allowable stress = 77,000N/mm^2

The amount of Torque transmittable seems very low.

11. Aug 5, 2009

### CFDFEAGURU

I have 4.15x10^7 N-m

That is a lot of torque.

12. Aug 5, 2009

the figure i am getting for J is around 6.5E-8

13. Aug 5, 2009

### Q_Goest

Check the allowable stress. It's about 2 orders of magnitude higher than a strong grade of steel.

14. Aug 5, 2009

The allowable stress figure that i have is 77KN/mm^2.

15. Aug 5, 2009

### CFDFEAGURU

For J,

J = PI/2(r^4) = 3.141592/2*(70^4) = 1.570796*(24010000)=37714811.96 mm^4

16. Aug 5, 2009

### CFDFEAGURU

Are you using all the correct units?

17. Aug 5, 2009