Confused About Forces in Bearings: Getting Reactions in Axial Direction

[Tekneek]

I was confused about this example from a book. After putting in some numbers I got the forces circled in green and blue to be negative. Does this mean the directions for the forces shown is incorrect, and so I should switch the directions before calculating the reaction forces in the bearings (x marked in red).

Also how should i go about getting the reactions in bearing in axial direction (s+p2)? Its pretty simple if I just have one axial reaction force, but with two bearings I am not sure.

Thanks

 

[JBA]

It appears that in B they are only concerted about the reactions on the driving spindle and not any of the components beyond that point. The orientation of the force vectors on that component will always be opposite to those shown in Figure A that represent the forces acting on the bar end connected to the drive spindle.

 

[Tekneek]

It appears that in B they are only concerted about the reactions on the driving spindle and not any of the components beyond that point. The orientation of the force vectors on that component will always be opposite to those shown in Figure A that represent the forces acting on the bar end connected to the drive spindle.

So if I want to calculate the reactions on the bearings should I just keep the negative, not changed the direction of my arrows and proceed with the calculations?

 

[JBA]

Yes retain the current forces as shown and treat them as forces on the end of a beam with two supports. At the same time, if you decide to extend your analysis to include the bearings then for a complete analysis you will need to include the forces from the drive pulley/gear on those elements as well.

 

[Tekneek]

Yes retain the current forces as shown and treat them as forces on the end of a beam with two supports. At the same time, if you decide to extend your analysis to include the bearings then for a complete analysis you will need to include the forces from the drive pulley/gear on those elements as well.

So I plugged some numbers into get the forces and also added a force from drive pulley. Does my calculations for the reactions at the bearing look correct? Thanks.

 

[JBA]

Your bearing reaction directions in the top diagram look correct; but, what does the 94.86 at the left end represent?

 

[Tekneek]

Your bearing reaction directions in the top diagram look correct; but, what does the 94.86 at the left end represent?

94.86 is the force from a pulley. Also, wouldn't the bottom diagram be the one with correction bearing reaction since I got negative values for the reactions (Raz and Rbz) when i solved them?

 

[JBA]

The reaction arrow directions for the spindle and the bearing B in the top diagram are correct. Did you use the x load direction at P3 shown in the top diagram or the bottom one? The P3 and all of the other forces shown in the bottom diagram at the tool contact point are tool reactions that are opposite to the reactions on the bar and ultimately on the spindle. If you have done the correct analysis then the horizontal x force at the spindle should be in the same direction as P3 in the top diagram.

PS I suspected that the end load was for the pulley, but I wanted to be sure.