How to secure shafts?

[jwatte]

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!

[Azraels]

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.

[jwatte]

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.

[waltr]

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.
http://www.mcmaster.com/#c-clips/=lvsa5q

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.

[jwatte]

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

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:

[Gertlex]

Seems like shaft collars would be a good bet for this as long as you don't get the absolute cheapest ones you can find.  Nylon tipped set screws, or a flat on the shaft (for the set screw to sit in) seem like a good approach.  Ebay has a good selection of not-horribly priced shaft collars.

If you have the capability to do threaded ends of the shaft, that's a good way, too, but almost certainly overkill.

[jwatte]

If you have the capability to do threaded ends of the shaft, that's a good way, too, but almost certainly overkill.

I have the option of trying a tap and die set on stainless steel, or figuring out the single-point-threading settings on the lathe... something I've never done before.

So, if "it's a bother to put threads on there" is the only reason not to do it, then probably I'll try that :-) If that doesn't work, I'll look for shaft collars and clips as options.

[waltr]

Since you do have a lath available, cutting grooves for 'C' clips would be easy.
I think 'C' clips for this would work well.

[jwatte]

AAAH!!!

I cut the shafts to length, and ground the edges with a millimeter of 45 degree taper.

I tried hand-cutting threads by clamping a dire to a drill press table and fixing the shaft in the drill chuck and then turning the drill by hand (with pliers to get leverage) while putting a little weight on the handle of the drill. Using SafeTap cutting oil/esther.

After 10 minutes, I had about 2 threads' worth of progress on one side of the first shaft. Man, that's tough going in 303 stainless! (I usually work with aluminum ;-)

So, yeah. Lathe. This will be my first time single-point threading, and if that also doesn't work, I'll do the groove/clips. Either way, it'll be done! (I prefer threads/nuts because I can adjust the amount of holding force/position.)

[waltr]

Ok on the progress report.
Yea, SS is much tougher than just low carbon steel and many times tougher than aluminum.

Hint on cutting the threads on a lath.
 Turn the thread tool upside down an run the lath in reverse.
This way the thread is cut from the smooth part of the shaft off the end of the shaft and allows time to disengage the power feed.
The normal rotation the thread tool is moving towards the chuck and if you don't disengage in time it crashes into the chuck, jams or moves the shaft in the chuck loosing the index.

[jwatte]

Thanks, Waltr! I'll try that next time.

So, yeah, I learned single point threading, and it went pretty well. Until I hit a "bump" caused by "deferred maintenance" on the lathe at the workshop -- sometimes, it false double starts. Even though I hit the dial indicator just right, it decides to start half off, and take off the entire thread I've been building up, burn my tapping oil to smoke, and snap off the shaft. Grr.

So, yeah. Clips! Good idea! I hadn't thought of that until you said it. It's off to McMaster I go. I'll have to be precise in measuring where the clips will go, or perhaps use some washers to pad it out. Also, I'll need some more quarter inch centerless ground 303 rod...

[waltr]

Agrrr...been there.
Good luck on your next try.

[Gertlex]

Painful was what came to mind when you initially mentioned threads on stainless steel.  I had enough trouble with aluminum (and maybe did soft steel too?)... Been a few years since I touched those machines, though, so didn't say anything, hehe.

[jwatte]

Actually, I kind-of enjoyed the threading while it was going well. Without that indicator problem, I would have totally made it!
(I think the problem is actually with the gear for the start indicator; it might be missing a tooth or be loose or something...)

Just shaving .015 off each side to take .250 down to .220 for fitting C clips will be a piece of cake by comparison. I have new rods and C clips coming from McMaster any day now :-)