Angle of twist between spring hooks 1

[Words_In_Sequence]

Hello,

I am having trouble puzzling through how to specify the allowable twist for a tension spring with parallel hook ends. We allow for a large deviation between the two hooks at the opposing ends of the spring (+/- 25 degrees of one hook relative to the other). For simplicity the drawing I've attached shows one surface as Datum A with an arrow and note pointing to the other hook specifying how much we want to allow it to deviate (twist) from parallel to A. What I would like to know is what is the best/most clear way to show the supplier we allow for one hook to be "twisted" out of alignment by 25 degrees either way relative to the to other and whether a datum call out is appropriate or a note describing what we'd like.

 

[3DDave]

I would use the OD of the spring as the primary datum feature, RFS, and then the width of the one hook as the secondary datum feature and then the width of the other hook would be controlled with an angle with a noted that the angle is measured relative to the primary and secondary datum features.

The standard Y14.5 doesn't have an allowance for angular tolerances and is based on converting all angle tolerances into linear or radial offset zones.

A profile of surface tolerance isn't quite right as it doesn't allow explicit angle variation and if you made a really large tolerance that would accept the hook being twisted in some way or bent to the side; lots of compliant shapes that might occur to the maker to allow.

I suppose, with a large enough stack of feature control frames, one could nail this down, but your spring maker will not be happy.

Will it matter if the hooks are opposite or need to face the same direction? That might also be worth noting.

 

[Doug Hunter]

I second 3DDave on this one.

 

[Words_In_Sequence]

Thank you 3DDave for you detailed reply. And thank you Doug Hunter for affirmation of 3DDave's response.

For 3DDave I do have another question. When you say that the width of the other hook "would be controlled with an angle with a noted that the angle is measured relative to the primary and secondary datum features" mean for this to be done inside an feature control frame correct? I've attached my updated print to show how I interpreted your response. The 999 value for the angularity tolerance is simply a placeholder.

 

[3DDave]

Yes.

The trick is that if you were able to accept +/-10º from a nominal 45º angular offset, then angularity or profile or position would not directly allow that.

 

[Burunduk]

Specify an angular (degrees or minutes) tolerance in a feature control frame and someone checking or approving or working by/to the print may eventually say it is "invalid" / "illegal" / "incorrect" or that you don't know what you are doing even if you do.

I'd rather do something like that: