Validity of Composite Positional Tolerance

[Jacob Cheverie]

I have a print that has a composite position tolerance on one feature of size. Y14.5-2018 contains section 10.5 titled "Pattern Location" that goes on to discuss composite positional tolerancing and multiple single segment positional tolerancing.

Is it valid to have a composite positional tolerance on a single feature of size and not a pattern? The explanations in Y14.5 imply that a pattern is required. It makes sense to me that it wouldn't apply to a single FOS, just trying to get some other opinions.

The next point of interest to me is multiple single segment positional tolerances. This description is also grouped into 10.5 "Pattern Location" and the wording seems to imply that you can only apply multiple single segments to a pattern. This doesn't make sense to me, but perhaps I am just not seeing it clearly.

 

[Belanger]

Composite position is only for patterns, because the lower portion (FRTZF) doesn't control location to the datums, thus the lower portion's only location aspect would be of the features within a pattern to themselves.
But multiple single segment position can be applied to a single feature, because the lower portion has location control to the datums.

 

[chez311]

Regarding composite position, a brief review didn't come up with anything that explicitly says a composite position tolerance can ONLY be applied to patterns. That said, the typical mantra with position tolerances is if it doesn't do its main job (namely - maintain position either between features or between a feature or features and a datum feature) then it probably shouldn't be utilized. Your lower segment for a single feature, specifically named Feature Relating Tolerance Zone Framework or FRTZF, is not doing its main job of maintaining your position tolerance between features. The salient question would be why couldn't you instead use an orientation tolerance instead of the lower segment/FRTZF of a composite position tolerance? This would be many times more appropriate in my mind.

As far as multiple single segment, this is a special case and name applied to the simple act of applying multiple position tolerances to a pattern of features. There is nothing stopping you from applying multiple position tolerances to a single feature.

 

[Jacob Cheverie]

Thanks Belanger, that makes sense.

chez311,
10.5.1 (Y14.5-2018) states "Composite positional tolerancing provides an application of positional tolerancing for the location of feature of size patterns as well as the interrelation (constrained in rotation and translation) of features of size within these patterns."
To me, that seems restricted to patterns. Also, as you point out, what exactly is the meaning of the FRTZF if you only have one feature?

Reading 10.5.2 on multiple single segments a little more carefully seems to show that it isn't restricted to patterns, so that is the way to go here. I thought the multiple single segment was just a different specification with a different DRF and I didn't see why it couldn't be used on a single feature. I wasn't reading carefully enough is all.

Thank you.

 

[chez311]

Jacob,

I guess I'm being pedantic in saying theres nothing that says it CANNOT be applied to a single feature. I agree the wording seems to only support use in a pattern, as well as the meaning of its definition. I would not use it either for the aforementioned reasons, and I don't necessarily want to open the can of worms I was just kind of playing devils advocate for those that might argue that a position tolerance could be utilized on a single feature with no location constraint to the specified DRF and no relevant pattern/grouping mechanisms to other features like simultaneous requirements. Hence why I said its "not doing its main job."

In that same vein since composite tolerance was used in the original print (lower segment would have only orientation requirement to the DRF) and you wish to replace it with multiple single segment, would the lower segment of your proposed multiple single segment tolerance fall into the above category I mentioned (no location constraint to DRF, no applicable pattern/grouping mechanisms)? If so, I would very highly recommend utilizing an orientation tolerance instead.

 

[axym]

Hi All,

I agree with what chez311 said.

Evan Janeshewski

Axymetrix Quality Engineering Inc.

http://www.axymetrix.ca

 

[Jacob Cheverie]

chez311,

I get what you're saying. In my case there is no pattern or grouping mechanism as you call it, but there is a location constraint to the lower tier DRF. Position would be the way to go on this one, I just believe it should be dual single segment over composite.

Thank you for the advice.

 

[Belanger]

Jacob, if it's a composite position FCF, there there is no location constraint in the lower tier to its DRF. Or are you saying that the intent was to have such control?

 

[Jacob Cheverie]

Belanger,

I apologize for being unclear. What I meant was that there would be a location constraint to the lower tier DRF if the positional tolerance were separate single segments.
If I understood chez311 correctly, he was saying that if the control is converted to single segments and there is no location constraint on the second segment, but rather a rotational constraint, an orientation tolerance would be more precise than a location tolerance.

 

[chez311]

Jacob,

If the intent was to have location constraint to a DRF which is able to constrain location of the feature of interest in the second or lower frame then composite position was never the correct control, regardless of if we say it can or can't be used on a single feature.

if the control is converted to single segments and there is no location constraint on the second segment, but rather a rotational constraint, an orientation tolerance would be more precise than a location tolerance.

Essentially yes, though not just more precise but I would say an orientation tolerance would be the proper specification and position the improper one in that case (orientation/rotation constraint only). As I suggested before one could make some arguments otherwise, I just don't think they have much merit.

 

[Jacob Cheverie]

chez311,

I agree 100%. I have to reach out to discover the true design intent and whether a composite control is desired before I proceed. This particular part has been measured improperly (to the print) in the past with both segments being treated as if they were single segments, so I am not sure what is the actual desire.

Thank you.