true position of a rectangular feature

[Ksplice]

Hi,

I'm working on a project where I want to control the true position of a rectangular feature within a diameter tolerance zone to 3 datum's. My problem is that we want to check this new part with a Gage with round holes in it, and so the tolerance zone we will be inspecting will not be circular but oval. This is because the feature is rectangular. Is there a way to call out an oval tolerance zone on a drawing or am i pretty much stuck with calling out a rectangular true position zone? I would go that way but I don't want to loose the tolerance gained by calling out a oval zone.

thanks,

kyle

 

[pmarc]

Ksplice,
I assume this rectangular feature mates with round hole in real application, correct? If not, you have to be aware that your inspection method is not really proper to verify the design against its functionality. That is the first thing.

If however verification with the use of a gage with round holes is functionally justified, I would suggest utilizing diagonals of the rectangular feature in conjuction with positional tolerance at MMC in order to find a virtual condition boundary at diagonal directions. The minimum diameter of gage hole will be determined by that VC size.

 

[Ksplice]

yes the part mates with a circular hole. but if I call out the diagonals true position within a circluar tollerance zone, i still have the problem of how to gage the part becasue I would still have to keep the center of that rectangluar within a circular tolerance zone. the gage hole would still be oval..

 

[Belanger]

I'm trying to picture this diagonal business, pmarc. Are the diagonals considered features of size?

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

http://www.gdtseminars.com

 

[powerhound]

Is there any way you can post an illustration of what you're trying to do? I'm having trouble imagining how what you're saying makes any sense but it's probably just my misunderstanding of your explanation.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[pmarc]

J-P,
I do not see a reason why both diagonals could not be treated as FOS - two sets of two opposed elements (corner edges) associated with size dimensions.

Ksplice,
Positional callouts on diagonals should not have diameter symbols preceeding tolerance values, but (M) modifiers need to be there in order to introduce virtual condition concept.

 

[powerhound]

The problem I see with corner edges being a FOS is in applying rule #1. All other regular FOS will possess at least two of the four form characteristics. This one might possess one. I know the standard doesn't specifically say that a feature must meet the criteria of rule #1 in order to be considered a FOS but to me it only makes sense. Maybe I'm just off today.

Powerhound, GDTP S-0731
Engineering Technician
Inventor 2010
Mastercam X6
Smartcam 11.1
SSG, U.S. Army
Taji, Iraq OIF II

 

[Belanger]

A feature of size must have opposable points -- we often think of the idea of calipers grabbing those points. That's why I question the corner points as FOS. But I'm still intrigued by pmarc's suggestion.

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

http://www.gdtseminars.com