Thread form error with GDT 3

[gabimo]

How to control the straight thread form variation/ form error with GD&T? (Unified UN, UNEF, straight thread--internal/female or external/male threads)

At work, people gave some creative suggestions: to apply total runout, to apply circularity/ roundness along with the positional requirement.

Is any of these a good idea?
Or maybe other suitable solutions, you can advise.

 

[Belanger]

Yikes -- I didn't know that optical comparators are "passe." A few of of the places I consult with use that as their main inspection device.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[mkcski]

John-Paul

Not passe per say (pun intended). But since a lot of mfg moved to "other parts', they are not as prolific as before. I teach for "die-shops" that make "2D" parts and they still use them.

Certified Sr. GD&T Professional

 

[JNieman]

@Belanger,

This thread was the first time I heard the sentiment as well. This is the first company I worked at which has any, and I think it's a pretty useful tool. I've used it for many quick checks and doing some investigation. We have more expensive and elaborate vision systems but those are in a building ~100 yards away, opposite our parking lot and, well, I guess I'm lazy

We maintain calibration and get it verified by a 3rd party on an annual basis - if it ain't broke, why stop using it?

 

[Belanger]

I guess the mantra that "CMMs can do anything!" has led to optical comparators being relegated as the little brother. But yes, a comparator is still very useful for many checks.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[gabimo]

So, where this thread migrated:

Would you trust a gage (thread ring) or a comparator (with mylar thread form) when checking an external thread?

What about if these inspection methods provide conflicting/opposing results (good/bad parts)?

 

[3DDave]

As I wrote before:

1) either don't create designs that depend on them
2) they don't affect anything because the affect is immeasurable.

 

[greenimi]

Dave and all,

I guess the OP's question is a more general than specific to his case.

ASME B1.3M states: "“Within each gaging system, a choice of gages is specified for each characteristic. Acceptance by any one
gage specified for a characteristic shall be the criterion for acceptance of the characteristic.” "

Now, how the comparator came to play, I 'll let more experienced gentlemen to chime in.