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I have an aluminium bearing holder attached to one end of an aluminium plate as follows:

enter image description here

The bearing holder is attached to the plate by two bolts on the bottom. The intended setup is to attach a relatively heavy load to the right hand side of the shaft. To reduce stress on the two bolt holes in the plate, is it a good idea to have a lip on the plate as shown? Will it actually have any effect? Ideally I'd like to fasten the bearing holder through the lip, but I'm trying to avoid machining from the side and stay away from 4-axis machining.

Are there better ways to reduce the stress on the holes?

Any advice appreciated.

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    $\begingroup$ How is the load applied to the shaft? $\endgroup$ – Solar Mike Jun 25 '20 at 18:50
  • $\begingroup$ @SolarMike It's radial to the shaft -- due to gravity. $\endgroup$ – Kar Jun 26 '20 at 0:26
  • $\begingroup$ A standard pillow block won't do it ? $\endgroup$ – blacksmith37 Jun 26 '20 at 1:34
  • $\begingroup$ @blacksmith37 I'm afraid not due to size constraints. $\endgroup$ – Kar Jun 26 '20 at 1:36
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In general the idea of bolt connections is that there should be no stress on the holes themselves. The purpose of bolts is to push the surfaces together so that the friction between the surfaces takes on the stress. So its important that the torque on the bolts is correct and the primary force direction isnt upwards in this case. (If it is bolt from sides)

If on the otherhand your design relies on the bolts shearing then the lip probably will help a bit. Though not much of a help since the structure is way weaker than if there is sufficient friction between the surfaces. However, the lip may help you in locating the part well.

But its hard to know without knowing your load conditions and magnitudes.

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  • $\begingroup$ But in my setup, I'm not sure if friction plays a large enough role. If a downward force was exerted on the end of the shaft, the bearing holder would tilt forward. Because of the two bolts on the bottom, the plate would bend and the front of the holder should press against the plate. My concern is whether the back of the holder would lift away from the plate, and thus, there might be a need for a side bolt? $\endgroup$ – Kar Jun 26 '20 at 1:34
  • $\begingroup$ @Kar you need to calculate what the actual situation is. $\endgroup$ – joojaa Jun 26 '20 at 5:20
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Logically I would use 4 bolts. Since you expect a moment to develop in the y axis and x axis you ought to have bolts suffice to resist those forces with a safety margin of 1.15 of the maximum allowable force.

An additional 2 bolts through the vertical face would be a good idea by extending the lip upwards to the top of the bearing case that these new bolts would be acting horizontal to the vertical bolts. A couple angular webs welded in place either side of the shaft housing would resist moments carried by the bolts, better. How you practically apply this is up to you because we cannot know what else the shaft housing is fitted into.

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  • $\begingroup$ Thanks. Can I ask what angular webs are? $\endgroup$ – Kar Jul 1 '20 at 6:02
  • $\begingroup$ Angular webs are triangular plates welded to the two independent surfaces perpendicular to the direction of force as resistive components. Usually steel plate from 2mm to 20mm thick. If welded to bearing housing and base plate you wouldn't need bolts at all. $\endgroup$ – Rhodie Jul 1 '20 at 15:08

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