Calculating the force on a shaft

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Discussion Overview

The discussion revolves around calculating the axial and radial forces on a shaft with attached bearings, considering a weight load applied to a plate on the shaft. Participants are examining the methodology for these calculations, including the use of free body diagrams (FBD) and the identification of dimensions.

Discussion Character

  • Technical explanation
  • Mathematical reasoning
  • Debate/contested

Main Points Raised

  • The original poster presents a calculation for axial force (Fya = 153 N) and radial moment (M = 191 Nm) based on a weight of 10 kg and an additional load of 37.5 kg.
  • One participant suggests that the free body diagram (FBD) should include the bearings and their forces in the calculations.
  • Another participant questions the clarity of the dimensions used in the calculations and requests symbolic representation of these dimensions for better understanding.
  • A further reply emphasizes the absence of reaction forces on the upright arm in the FBD, raising concerns about the completeness of the analysis.

Areas of Agreement / Disagreement

Participants express differing views on the adequacy of the original calculations and the clarity of the dimensions used. There is no consensus on the correctness of the approach or the calculations presented.

Contextual Notes

Some dimensions in the calculations are not clearly identified, and there is a lack of reaction forces in the FBD, which may affect the accuracy of the analysis. The discussion does not resolve these issues.

Blad9
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I would like to attach bearings on a shaft, see: https://www.physicsforums.com/showthread.php?p=3856547#post3856547

Therefore I would like to calculate the axial and radial force on the shaft, so I can select the right bearings.

The picture looks a as following: http://i39.tinypic.com/kd1naq.jpg
kd1naq.jpg

So I have a shaft, with a plate attached on it with a weight of 10kg. A load will be putted on the plate wit a weight of 37,5kg. Now I would like to calculate the axial and radial force on the shaft.

Sketch:
http://i41.tinypic.com/kd1iqx.jpg
kd1iqx.jpg



Sum Fx to A = o

Fxa = o

Sum Fy to A = o

(-375N x 0,625 x 0,3125) – (100 x (0,725/2)) + Fya x 0,725 = 0
-73,2 - 37,6 + Fya x 0,725 = 0
-110,8 + Fya x 0,725 = 0
Fya = 110,8 / 0.725
Fya = 153N

Som M t.o.v. A = o
M in a = 375 x (0,725 – 0,3125) + 100 x 0,3625
M in a = (375 x 0,4125) + 36,25
M in a = 191Nm

The shaft would have an axial force of F = 153 N and radial momentus of M = 191 Nm according to this calcuation.

Does this look ok, or should I calculate it completely differently?
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You need to go back and shows the bearings in your FBD, and include their forces in your force and moment sums.

Also, it is not entirely clear where some of your dimensions came from; can you identify them, please?
 
What dimensions are not identified? Do you see the picture?
 
Yes, I saw the picture. One of the difficulties is that you have worked entirely with numerical values, rather than giving symbolic names to each of your dimensions. If you gave each of them a symbol, before plugging in the number, then it would be much easier to see where each item came from.

Also, in the FBD, I do not see any reaction forces on the upright arm; why?
 

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