Snap ring for fractionally sized shaft 2

[slashragnarok]

So I have a design for a personal weightlifting bar I'm working on (pic attached). My question is regarding the snap ring size. The red external snap ring fits on the shaft (magenta) and the two washers on either side along with the internal snap ring further to the left prevent axial movement of the shaft. Now the shaft diameter is 28.5 mm whereas the snap ring in the model is for a 28 mm shaft. The groove depth is according to DIN standard for a 28 mm snap ring. Will this work?

 

[tbuelna]

Why not cut down the outer section of the shaft to 28mm? If you use a spiral wound type retaining ring rather than a conventional snap ring you can probably get the spiral wound ring to fit over the .5mm larger shaft end. But even if you reduce the outboard section of the bar by .5mm so that a conventional snap ring will fit, it should still be plenty strong for your application. A 28mm external snap ring has a shear strength of over 2900lbf.

 

[slashragnarok]

Do you mean cutting down the groove or the entire shaft dia?

 

[Jboggs]

It sounds like the wrong size snap ring is shown in your model. Why not just get a retaining ring designed to fit your 1-1/8" shaft?
They're available everywhere. Try McMaster-Carr or Rotorclip.

 

[slashragnarok]

I'll try but I'm in India so everything's in metric. Even DIN standard has everything in mm.

 

[slashragnarok]

But in any case what's the standard procedure for selection of rings for odd sized shafts?

 

[Jboggs]

Maybe everything in India is metric, but I'm confident you can get inch size retaining rings in India, just as we can get metric sized components in the US. I'm sure there are some component importers that specialize in inch size components.

As for manufacturers, Rotorclip (

http://www.rotorclip.com)

is an international company. Contact them or their Indian distributor. I'm sure they can help.

As for the procedure to use standard rings on "non-standard" shafts, you have to create a "standard" configuration (shaft OD, groove OD, groove width) on your shaft to use the ring you select. Any good retaining ring catalog will give you those dimensions.

 

[slashragnarok]

Thanks I got you. So in my case I'll probably have to cut down the groove or search for the right sized ring.

On a separate note, if you've seen my drawing I'd like some advice. The sectional view that you see is of a shaft that'll rotate w.r.t the sleeve on two bushings, of which one is visible. Now there are no clearances between the washers and retaining rings except the mandatory clearance caused by the differences between the sizes of the snap rings and the widths of their respective grooves. The whole system's going to be lubed. Would the rotation be hampered due to the aforementioned lack of additional clearance between the washers and rings?

 

[Jboggs]

"probably have to cut down the groove or search for the right sized ring."
Preferred Choice: Use the right sized ring.
If you cut down the groove, don't stop there. Don't forget the ring has to go over the OD of the shaft, so you will have to modify it too. Rings are designed to go over shafts of a specified size and still fit tightly in grooves of the specified size. Do not try to expand a ring to go over a shaft larger than its specified size.

"Would the rotation be hampered due to the aforementioned lack of additional clearance between the washers and rings?"
Absolutely! Always design in some axial clearance. How much depends on the precision of your manufacturing process. The main thing is you never want a metal-to-metal condition as your default. Metal-to-metal = friction.

 

[slashragnarok]

"Absolutely! Always design in some axial clearance."

Right. Now the question is how much is some? Keeping in mind the clearances created by the difference in the snap ring sizes and groove widths, I already have 0.55 mm of axial play. Is this enough? If not could I adjust the washer thicknesses (by grinding them?) during the testing phase? I would also like to specify here that the whole washer, snap ring assembly is going to be bathed in some lubricant like SAE 40 (a.k.a 3 in 1 oil).

 

[Jboggs]

"Is this enough?"
Only you can make that call. You're the one that knows what the operational result might be.
Just make sure it never gets to zero no matter what tolerance buildup occurs as parts are made and assembled.