Perpendicularity of a spring?

[greenimi]

I seen a drawing where the OD and ID of a cylindrical /helical compression (with closed ground ends) spring are controlled with perpendicularity? Is this even a valid callout?

Datum feature A is the free length and OD and well the ID have a perpendicularity callout in .010(M) with A(M).

How the orientation can even be controlled? Can the maximum side deflection be even keep under control this way or you have seen a better way to do it? Any other suggestions?

I kind of know what the engineers are looking for in this case: the spring is sitting between 2 plates with a shaft going thru its ID and a bushing over its OD. The idea is to not let the spring rub against the shaft (ID) or the bushing (OD), so the deflection/ tilt of the spring must somehow be in some tolerance.


Any other good examples or standard to be used?

 

[dgallup]

I generally make the OD of the spring my datum and specify the perpendicularity of the ground end face in the free condition.

I know some people like to control the spring deflection in a loaded condition but it is much harder to measure. You need some way to compress it to a given length between parallel plates and see how much it bows. It can be done but you probably need to measure every spring.

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[btrueblood]

In addition to the measurement problem, a typical wire compression spring will form a "barrel" shape when compressed. See any of Wahl's books on springs for more info.

Dgallup's method is the normal way of specifying, as that is how the grinding is done. Specifying in other ways just increases the cost, as does making the perpendicularity tighter than the standard methods can produce.