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I have a question regarding how are the vertical forces on a spur gear shaft are supported. I am currently doing my undergraduate (in final year) and have only dealt with gearboxes where the shafts axis lies in a horizontal plane. I am designing a device that requires the shaft to be vertical.

I understand how the bearing would support the axial and radial forces but what about the vertical forces, how could I support these (from the weight of the shaft and gears).

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  • $\begingroup$ Do a search on angular contact bearings. These are ball bearings designed to support axial forces in addition to radial forces. $\endgroup$ – Eric S Jul 26 '20 at 16:08
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A vertical force is either a axial, radial or combination of both depending on what part of it is aong the shaft and what is not. These describe all forces there can be on the simplified shaft system from bearings point of view.

If you turn the axis of shaft running vertically then the weight just becomes a axial load if the axis is on angle then part of the load us axial and part of the load radisl as per standard force composition rules. If you have hard time understanding this draw the image and all force arrows then turn it around so its in the exact same orientation you did analysis before. Same result.

The reason we do this is that the bearing is axisymnetric it does not matter as such which way the force is in the radial direction just its magnitude. Offcourse the bearing is very different in the axial direction.

So you would design it the same way but with possibly more axial load allowance.

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  • $\begingroup$ This makes perfect sense. Thank you $\endgroup$ – T.Ar Jul 27 '20 at 18:56
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There are roller bearings that are designed to take vertical loads like that if the loads are large.

Or there are thrust bearings, thrust washers or even taper roller bearings if the loads are not too large.

Based on other information the bearing can be an interference fit on the shaft to locate it or the shaft can have a shoulder machined to locate one bearing, leaving the other to slide to accomodate changes in dimension due to temperature change for example.

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  • $\begingroup$ Okay thank you. Will have a look through those $\endgroup$ – T.Ar Jul 25 '20 at 13:56

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