Slot called out for True Position and Full Radius at 2 end. 1

[cmmguy75]

Hi All,
Please see attached picture and help me out....
1/ Will 2 Radii need to be inspected for size? If yes what is a tolerance, +/-.002?
2/ What does True Position call for
(a) Mid point of slot width and center of 2 radii?
(b) Mid point of slot width or center of 2 radii?
(c) Mid point of slot width only?
---
For question 2, (c) is my answer.
To me, with True Position, 000(M), the matting part (pin/rod...) is only allowed to move .002" MAX (form reference datum with distance |2.558"|) if the width is made at MAXIMUM (.257").

Thanks!

 

[Belanger]

The position might best be thought of as controlling the boundary of the physical walls, not the mid point of anything. If you have access to the ASME Y14.5 standard, it goes into this in paragraph 7.4.5.1; also see Fig. 7-34. It's not wrong to think of the mid point or mid plane, but the boundary interpretation sometimes avoids confusion about how to find the mid-plane.
The maximum position tolerance will be .004 (because the size tolerance is ±.002). So if you mean that a mating pin can move .002 to one side (max) I suppose that's true. That mating pin will have its own tolerance of course, so there may be other variables to consider.

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

 

[cmmguy75]

Hi John,
From Fig. 7-33 on P125 (ASME Y14.5-2009), it stated "Tolerance zone equal to positional tolerance) which is ZERO for this case. Doesn't it use (M)to gain bonus here?
Thanks, Brandon

 

[Belanger]

I don't see any mention of a zero tolerance. The text within Fig. 7-33 says that "the tolerance zone (equal to positional tolerance)" is the unknown quantity "P." So that width of P is to contain the center plane if the slot is made at MMC. Half of P lies to the left of the perfect location and half of P lies to the right of the perfect location.
The figure doesn't mention it, but the value of P can presumably grow if the slot is made at a different size; that's called bonus tolerance.

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

 

[cmmguy75]

Thanks John for your clearly explanation.
(The ZERO Tol is in my example)

 

[Belanger]

Sorry -- I missed that you were translating Fig. 7-33 to your specific example which did have the zero tolerance! But I hope my posts help anyway.

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