Using runout on threaded feature?

[score33]

I was asked to review a dwg that uses runout to control a threaded feature.

This is not something I've ever seen before and can't find any use cases where runout is the proper control to use. Is there a case where you'd want to use runout on a threaded feature? If not, what's the argument against it? I would assume you want to control pitch diameter and runout would only control major diameter? How would you inspect this callout?

Thanks.

 

[3DDave]

Q: How would you inspect this callout?
A: I would make a fixture that holds the part and has a cylindrical track that is parallel to the axis of rotation with an arm that lies across the screw thread and has a wire that touches the thread at the pitch diameter. As the part is turned the wire follows the thread and pulls the arm along the track. A dial indicator is placed at the other end of the arm and rides on another track that is also parallel to the axis of rotation. The variation in the dial indicator reading is scaled to the account for the ratio of distances from the cylinder to the screw thread and to the dial indicator.

 

[score33]

Sounds like a complicated setup... do you know of any reason you'd want to call out a threaded feature this way?

 

[3DDave]

I hope it's because there's a need for it. I haven't had to create a mechanism that depended on it.

 

[KENAT]

What if the threaded feature is part of a linear actuator that requires very straight travel and there isn't room for a separate linear bearing or guide so the screw does the job.

We unfortunately have a couple of designs where this is the case - as some others in our industry appear to do.

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