GD&T Callout for true postion not based on diameter tolerance zone

[Spurs]

I am wondering how to do the GD&T callout on my drawing to achieve the following result using an attribute gage:

I have a bolt circle of 2 inches in diameter with 5 studs in the bolt circle equally radially spaced. The studs have a diameter of .250 +/- .005"

There is a hole in the center of the studs of .200" +/- .003" - labeled datum A. Datum B is the face that the studs are attached to.

For proper function of this device, each stud can be radially spaced at 1" +/- .004" from the center of .200" hole. Of course the angle between each stud is a basic dimension of 72 degrees. The tolerance on this is +/- 0 degrees except for a bonus if the stud is not at the maximum material condition. There is an additional bonus possible if the center hole is not at maximum material condition

How do I call this feature control frame for true position on the drawing?

What confuses me is that the true position of the studs really do not have a diameter tolerance zone. The tolerance zone is strictly radial from the center with bonus on angular postion if the studs are not at maximum material conditon. Hence the attribute gage has oval shaped holes for each pin to go through.

Can anyone enlighten me?

 

[Belanger]

Since you don't mention a potential bonus on the radial direction's tolerance -- you gave the number as 1 ± .004 -- then this is considered "regardless of feature size." Thus, an attribute gage can't really be used for that aspect of the question.

If you're willing to allow the MMC/bonus idea there, then it might be feasible. It would require two separate feature control frames (and an optional note under each saying "boundary"). I also suspect that each feature control frame should have B as the primary datum and A as secondary...

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

 

[Spurs]

I did not give a bonus on the radial positon because I was thinking that this +/- .004" would somehow be the tolerance in the feature control frame.

Is it possible that this is better defined as a profile callout instead of true position?

 

[dingy2]

I would use a bi-directional positional tolerance as shown on page 124 7-29 of the 2009 standard.

I would suggest the you have both directions in MMC so that an attribute gauge can be developed.

Radially, the feature control frame would show a tolerance of .008 (no diametrical tolerance zone)at MMC relative to primary datum B and secondary datum A at MMC. Please note that I changed the datum structure since the primary datum is the mounting surface.

In the other direction one would need to have another feature control frame with 0 at MMC relative to datum B and datum A at MMC.

Remember that you will have 2 feature control frames with separate requirements showing the direction of the tolerance.

That should do it.

Dave D.

http://www.qmsi.ca

 

[Spurs]

Dave
Are you talking about Y14.5-2009 on the standard that you are referencing?

 

[SeasonLee]

If you have standard Y14.5M-1994, pls go to page 140 Fig 5-42, it should be same as Y14.5-2009.

SeasonLee

 

[Spurs]

All

Thanks for the help - that is exactly what I was looking for