Relative Position Question

[Stephen Andrews]

I have a 4 hole bolt pattern which is the customer mounting feature. They want a (4X) true position on these holes to an ABC alignment, so that was easy enough. They also want a (4X) True Position to A, which is the plane in which they lie in. I just contstucted a feature set and did a true position as a pattern. Is this correct? There is a dimension option for position between, but I don't completely understand how that works. Any help or clarification on this is greatly appreciated.

[Glenn Downey]

It's been a while since i've dealt with anything like that, but if i remember correctly, what they are asking for is perpendicularity.

[Stephen Andrews]

We build oil pumps for almost all automotive manufacturers. The guys at GM do in fact view this as perpendicularity. Our engineers here that drew the print, say the callout is the position of the holes relative to each other. They have a True Position of .4 to A,B,C and a True Position of .2 to A.

[Matthew D. Hoedeman]

I think once it becomes a group of holes that it becomes a relative, if it is for a single hole, it is perp. By only including the A for the group, that means that the group itself can float side-to-side as well as rotationally AS LONG AS the individual TP is in spec, the pattern can move a little bit, how much depends on the individual TP and the group relationship.

I would use those 4 holes in a 2-D best-fit, trans & rotate alignment, then TP them to that.

[Stephen Andrews]

That sounds good Matt. By creating a feature set, and then doing true position as a set, am I only getting the origin of the pattern relative to current alignment?

[Glenn Downey]

Just out of curiosity, what would define it as a group. I can't say that i've ever encountered that. The 4X is individual, is there a symbol that ties them together?

[Matthew D. Hoedeman]

That sounds good Matt. By creating a feature set, and then doing true position as a set, am I only getting the origin of the pattern relative to current alignment?

Not a feature set, that dimension would give you the center of the set, not the relative TP of each hole to each other. The best fit alignment using the 4 holes, then TP each hole in that alignment.

[Stephen Andrews]

Your right Matt. I am currently doing feature set, I just wanted to be able to explain the numbers for position I am getting now. I plan to change to the best fit alignment using the 4 holes, and doing true position from that alignment. I need to be able to explain the diffrent in before/after numbers to make sure everyone is on the same page.

[Schlag]

The bottom portion of the Feature Control frame in a COMPOSITE is what ties the hole pattern together.

[John Riggins]

The requirement is for BOTH the pattern and the perpendicularity. Yes, both.

[Stephen Andrews]

Sorry for the late response...got tied up out on the floor. I appreciate all your help and insight. I am going to try this tomorrow if I get the chance and do some more studying on this. Thanks again.

[dph51]

Reference ASME Y-14.5 2009

section 7.5.1 Composite Positional Tolerancing.

Perp to -A- while maintaining postional location referenced in upper frame.

[John Riggins]

Reference ASME Y-14.5 2009

section 7.5.1 Composite Positional Tolerancing.

Perp to -A- while maintaining postional location referenced in upper frame.

The above makes it sound like one frame requires positional location and the other requires orientation (perpendicularity).
In fact, both are required in both frames.
The upper frame requires locational adherence to the datums referenced in a cylindrical zone.
The bottom frame requires locational adherence (in this case) of the holes to each other in a smaller cylindrical zone.

[dph51]

The above makes it sound like one frame requires positional location and the other requires orientation (perpendicularity).
In fact, both are required in both frames.
The upper frame requires locational adherence to the datums referenced in a cylindrical zone.
The bottom frame requires locational adherence (in this case) of the holes to each other in a smaller cylindrical zone.

+1
a better explanation. Thank you John.