Position/Tolerancing for Irregular Slotted Features

[mbezkrov]

I have a few slotted features that are atypical from a standard slot/hole. These are on a simple sheet-metal bracket.

The first two features are a pair which need to be located tightly to each other, but their location on the overall part is not as critical. My initial thought was to use a composite profile pointing at both features designating it as one; however, I am hesitant about putting a profile tolerance on this part because I think it drives the inspection requirements up unnecessarily. Is there a way to tolerance these in a more simple way such as a combination of composite position and simple +/- dimensions?

The second feature is a set of four slots that have a larger hole at one end to clear fastener heads (so that the fasteners do not need to be fully removed during service). Again, my initial thought was to use composite profile--however, is there a way for me to dimension these with a composite position instead so that these features can be checked with pins?

Thanks,
Matt

 

[mkcski]

At a quick glance, and assuming the entire shape/surface of the "holes" needs to be controlled, I would stick to profile. It might be possible to use the boundary concept in Y14.5-2009 figure 7-34 page 126, but I have no experience with it and how it might apply to your shapes and design requirements.

Certified Sr. GD&T Professional

 

[3DDave]

Since you have a custom problem, just define the inspection method using pins on the drawing. Maybe, after you put the requirement into words, some other symbolic method will be seen as applicable but, if you cannot put it into words, there is no chance there is a symbolic method.

 

[chez311]

I assume that since you are talking about pins and hesitation to utilize a profile tolerance that only portions of the shown slotted features are important, correct? (ie: the circular portions and those regions adjacent to them) If this is the case, what about using an all over multiple single segment profile and then applying a separate tolerance only on the critical features which has the same DRF as the lower segment of the all over tolerance, so its held together with simultaneous requirements? Also a non-uniform tolerance zone could be an option as well per 8.3.2.2 - not sure if any of this is helpful though as its only opens up the tolerance slightly vs. an all-over tight profile tolerance.

That being said, technically all (3x 3.5 dia and 1x 5 dia) the assumed critical rounded portions except for the 1x 3.5dia on the slotted feature with 3deg angled sides are FOS as they contain opposed points and could be toleranced with position, however if the intent is to control the rest of the slotted feature with profile, I'm not sure how that would be reconciled as the position would require a directly toleranced diameter which would be attached/tangent to a the slot width which would be required to be basic for a profile tolerance. Perhaps you could treat the critical rounded portions and their tangent sides as an open ended slot?

 

[mbezkrov]

Thanks guys. I went ahead and just used an all around compound profile for both of them, and leave it up to the inspection house/vendor to figure out how they want to meet that tolerance.

 

[mkcski]

I don't think you just "settled" for profile. In the past profile was avoided because the manufacturing world lived in 2D space. With the ubiquity of 3D models, multiple axis machine tools and CMM's to define, communicate, manufacture and inspect 3D space, profile is becoming more mainstream, at least from what I see in my (limited) travels.

Certified Sr. GD&T Professional