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How to secure shafts?

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I have a suspension where an A frame is rotating on a shaft (axle.) This shaft is suspended between two brackets through two ball bearings mounted in the brackets, with a lip in the mounting hole to keep them from moving "inwards." However, nothing prevents them from moving "outwards."
I can think of many ways of fixing this. For example:
1) Rely on press-fit bearings to fit well enough to not move.
2) Use a shaft collar with set screw right outside the bearing.
3) Use a pin through a drilled hole in the shaft.
4) Thread the ends of the shaft and use a lock nut.

My current plan is 4) but I have very little experience in mechanical design and building, so any suggestions, comments, references, or feedback you have would be very much appreciated!

Do you mean your worried about the bearings slipping out of they're mounts? Usually they are a good enough fit if they were commercially manufactured for each other. But if they are loose enough to worry about then a shaft collar will still let it slip out. You would need a retaining plate to secure the bearing with a hole large enough to let the shaft spin freely. I use washers with a larger diameter than the bearing and drill holes around outer edge for mounting over top of bearing.

If its the bearing slipping on the rod then I would make the decision based on how often you are going to be disassemble/reassemble. If its done and your not going to take it back apart often then I would go with threading the shaft or the shaft collar. If you need to keep taking back apart for experimenting then go with the shaft collar or even a rubber grommet that fits snugly on the shaft.

I'm making all these parts (except I'm buying the actual bearings) :-) The bearings "snap" into their mounts, but they can be pretty easily pushed out.
As the bracket mounting holes are opposed to each other and the bearings are on the same shaft, I don't worry about that, as long as the bearings stay fixed on the shaft! (Or, the shaft stays fixed within the bearings.) I hope I won't have to dismount this too much; it's taken a lot of designing and prototyping to get to this point.

I get the shaft by filing off a little bit on a slightly oversize quarter-inch 303 stainless rod; the bearings are cheap 1/4"-3/4" bearings by the dozen from vxb. Thus, because I don't press the bearings on, the shaft has some slip to it.

It sounds like threaded ends with lock nuts isn't entirely crazy for making sure the shaft can't "wander" sideways through the bearings.

How fast is the shaft rotating?
Is there going to be any side forces on the shaft/bearings?

What about 'C' clips. The shaft end only needs a groove for the clip. The groove does need to be cut at the correct location on the shaft for proper side play.

Threaded shaft ends work if there are two nuts to lock against each other. These can be tricky so not to be too tight against the bearing. But, they can be adjusted to minimize axial shaft movement.


--- Quote ---How fast is the shaft rotating?
Is there going to be any side forces on the shaft/bearings?
--- End quote ---

This shaft is the chassis rotation axle for A-frames for a suspension (there are two of them per suspended wheel.)
Thus, it will not rotate a full revolution, just oscillate up and down with wheel movement relative to the chassis.
There will be some sideways force, because that's how driving/braking thrust is transferred to the chassis. I imagine driving over road bumps will also transfer some lateral force.
The wheels themselves have direct-drive mounted electric motors.

The actual A-frames are mounted on the shaft on the inside of the bracket pair, with oiled thrust washers between the A-frame and the bracket. The full mount looks something like this:


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