Fender Washer Strength: Determining Adequate Load Capacity for Wire Rope Tension

[nation99]

Please see the included sketch. I need to know if the fender washer I'm planning to use will be strong enough to not deform and thus reduce the tension on the wire rope. TIA, Dave

 

[Baluncore]

Welcome to PF.

Failure of the washer will depend on the unspecified inside diameter of the helical spring.

 

[nation99]

Failure of the washer will depend on the unspecified inside diameter of the helical spring.

Yes, forgot to include the spring info. Spring I.D, is 0.488 and the O.D. is 0.812. I should also mention that the aluminum ferruel will not have full contact with the fender washer due to distortion as a result of crimping it to the wire rope. Thanks.

 

[Baluncore]

Only the 0.095" wire centres the washer in the ID=0.488" spring.
For that reason, it is likely that the wire will not remain axial in the spring.

I am not saying the washer will fail, just that it will not constrain the position and alignment, to prevent buckling sideways of the spring.

 

[nation99]

I've considered that and am thinking about adding a sleeve to insert between the wire rope and the spring ID.

 

[Baluncore]

Washer annulus = ( 0.75 - 0.17 ) / 2 = 0.29"
Wire diameter = 0.095"
Sum of wire and annulus = 0.095 + 0.290 = 0.385"
That is less than the spring ID = 0.488"
So the washer can be pulled through the inside of the helical spring.

I would design a stepped seat to replace the fender washer.

 

[phinds]

Just get a bigger fender washer

 

[nation99]

You probably have guessed by now that I'm a DIYer and not an engineer. That being said, I do understand what you are suggesting is a possibility. Thus my original question...will the fender washer be stiff enough to maintain the load that it will see?

 

[phinds]

You probably have guessed by now that I'm a DIYer and not an engineer. That being said, I do understand what you are suggesting is a possibility. Thus my original question...will the fender washer be stiff enough to maintain the load that it will see?

If it isn't, just use 2 or 3 of them.

 

[Baluncore]

Thus my original question...will the fender washer be stiff enough to maintain the load that it will see?

If you have ignored the obvious failure modes, and so build a house of cards, that design failure may later be investigated by a Coroner.

Look for data on a stainless steel belleville = cone shaped spring washer, that has a greater outer diameter, and will not flatten at 150 lb.
https://en.wikipedia.org/wiki/Belleville_washer

Nesting two different belleville washers may help centre the wire in the helical spring.

You might also consider simply replacing the carbon steel spring with a stack of alternated stainless-steel belleville washers, that gives the same spring constant.

 

[Lnewqban]

... Thus my original question...will the fender washer be stiff enough to maintain the load that it will see?

I believe that it will be stiff enough, but the assembly will not be stable, as mentioned above.

I have created a scale drawing with the dimensions that you have provided.
Note how the magenta spring is free to move toward the right and go over the outside diameter of your washer.

At a glance, that washer is the only member of your assembly that looks marginally able to match the other beefy elements.

Another factor that may make things worse is the non-flat bottom of that heavy duty spring (if the spiral ends have not been squared and ground to be flat), which will transfer the load completely off-center to the washer, which will not remain horizontal.

Note how commercial spring hangers, rather than flat washers, have spring cups at both ends of the spring, in order to avoid the discussed problem.

As you don't have those metal cups, a simple rubber sleeve located inside the spring, having the proper OD and ID, could greatly help with stability.

 

[Nik_2213]

As described very well above, most springs are a poor match to this layout. They wriggle, squirm, create point-loads, lie skew and are generally 'a pain in the tool-kit'...

The flattened last-turns, centring sleeves, conical / domed washers, end-cups etc etc are each a part of solution. A flattened last-turn meeting sufficiently stepped washer at each end would seem simplest route. Also, if you hunt around, very thick washers are available. I've even seen them in craft-shops as 'loom weights', but their usual purpose is load spreading for foundation and similar heavy-duty fixings. I'm told they are handy as weld-on, bolt-through hard-points for sheet metal, where a stud's flange would not do.

( Think 'grommet' on fabric, be it ground-sheet or sail... )

 

[gmax137]

I would design a stepped seat to replace the fender washer.

@nation99 this would be a good approach. Maybe you or a friend has a lathe, these could be turned up in a matter of minutes. I would volunteer to do it for you but my lathe is out of service, I'm looking for a new motor...

 

[nation99]

I believe that it will be stiff enough, but the assembly will not be stable, as mentioned above.

I have created a scale drawing with the dimensions that you have provided.
Note how the magenta spring is free to move toward the right and go over the outside diameter of your washer.

At a glance, that washer is the only member of your assembly that looks marginally able to match the other beefy elements.

Another factor that may make things worse is the non-flat bottom of that heavy duty spring (if the spiral ends have not been squared and ground to be flat), which will transfer the load completely off-center to the washer, which will not remain horizontal.

Note how commercial spring hangers, rather than flat washers, have spring cups at both ends of the spring, in order to avoid the discussed problem.

As you don't have those metal cups, a simple rubber sleeve located inside the spring, having the proper OD and ID, could greatly help with stability.View attachment 333644

View attachment 333645

View attachment 333643

Thank you for your time and thoughts. The springs are plain and ground ends. I agree that installing a sleeve between the wire rope and the spring I.D. will add stability. All I want to do is to maintain tension on the wire rope and the spring is there to compensate for slight movement of the surrounding/supporting structure (treated wood). I'll continue looking for washers that may be a bit thicker. Thanks again!!

 

[Nugatory]

All I want to do is to maintain tension on the wire rope and the spring is there to compensate for slight movement of the surrounding/supporting structure (treated wood).

How much play are you expecting? @Baluncore has the right idea when he suggests a stack of Belleville washers for this amount of force.

 

[nation99]

How much play are you expecting? @Baluncore has the right idea when he suggests a stack of Belleville washers for this amount of force.

I chose this spring because it provides a range of tension that is appropriate for the application when it is at the mid range of travel which is 0.200"...0.400 from full length to solid length. Belleville washers would be a good option, but I think the cost of the washers required to get that amount of travel would be cost prohibitive.

Expected travel is unknown, but I can imagine +/- .125" possible due to expansion and contraction of the treated wood.