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Functional Gage for TOP applied at RFS

#1
Hi
I'm beginning in Functional gage design. I'm working in a gage for a product that has a hole which should be located relative to a plane( Datum A) and another holde (Datum B) at RFS. I've made some research and found that making a gage for this RFS method will be more expensive, difficult, time-consuming, you´ll need multiple gages, etc. but I didn't find any example of this gauges and how to use them.

Can someone help?
hank you very much!

Sorry, My English is very poor, I hope I've explained myself well.




2019-08-15_20h05_10.png
 

John Predmore

Involved In Discussions
#2
edrose- Your English is fine. Your question could be explained better with a picture of your part drawing, showing the geometry relationship between datum A, datum B and the hole you want to gage.
 

John Predmore

Involved In Discussions
#4
Hello edrose-
I agree a gage for RFS geometry will be more expensive and complicated. I think your first action is to ask the designer whether the reference to datum B must be RFS. It is common to add the MMC modifier in the feature control frame, to allow for a simple gage fixture.

If the designer says the geometry must be RFS, below is one idea of a spring-loaded movable tapered pin (see attachment list in elsmar.com). Another option is a spring loaded expanding locator pin (a web-search found a few companies selling these). I am not a gage designer, but I do know GD&T, and I understand your challenge of designing a gage. Good luck.


Hi Vikash,

You could use RFS pins (spring loaded tapered) for the holes and have the second pin mounted in a sliding block then use an indicator or a go/nogo feeler to check position. This takes the hole sizes right out of the measurement. Here is a screen dump.
I hope this helps.

Chris
View attachment RFS_Locator_Pin.pdf
 
#5
Hi @John Predmore, thank you Very much.
actually, the designer confirmed the hole position should be RFS.
From your attachment, I understand that these RFS Pins, could be useful for the B Datum, but I don't understand the part where @cwarren says: "have the second pin mounted in a sliding block then use an indicator or a go/nogo feeler to check position. This takes the hole sizes right out of the measurement. "
Regards
 

John Predmore

Involved In Discussions
#6
I don't understand the part where @cwarren says: "have the second pin mounted in a sliding block ... This takes the hole sizes right out of the measurement.
In the virtual world of GD&T, the datum of hole B and the location of hole C is the centerline of each hole. The hole size is not a factor in the location of the hole. In the physical world, it is more practical and less expensive to make a gage touch the perimeter of the hole since the centerline does not exist in the physical world. The idea of a tapered pin or the expanding pin in a physical gage is an attempt to reference the centerline location regardless of feature size (RFS). If the diameter of either hole must be measured in manufacturing, the measurement of diameter will be a different gage.

The comment from CWarren was taken from an earlier conversation. His comment about first and second pin have nothing to do with your design. I quoted Cwarren only to show the attachment illustration of the movable tapered pin. There are other potential solutions to your gage design. You have to develop the solution which works for you.
 
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