# 506 MD 2008 NCEES sample



## Lily (Oct 16, 2010)

Does anyone knows what does the box with + 0.005 A B C means?

I thought the smallest diameter of the hole is 0.265 and the largest is 0.275. apparently not...

Thanks,

Lily


----------



## Relvinim (Oct 17, 2010)

Lily said:


> Does anyone knows what does the box with + 0.005 A B C means?I thought the smallest diameter of the hole is 0.265 and the largest is 0.275. apparently not...
> 
> Thanks,
> 
> Lily


The smallest diameter of the hole is .265 but you have to subtract for the positional tolerance of .0005 for both the pin and hole. This means the pin can't be bigger than .265 - 2(.0005). Hope this made sense.


----------



## Rafa (Oct 17, 2010)

The smallest diameter of the hole is .265 but you have to subtract for the positional tolerance of .0005 for both the pin and hole. This means the pin can't be bigger than .265 - 2(.0005). Hope this made sense.


----------



## Lily (Oct 18, 2010)

That's very clear on why the diameter of the pin should be 0.265-2*0.005. However, is the sign before the 0.005 a plus? if yes, is it possible to have a minus instead? and what would it mean? Thanks!


----------



## Relvinim (Oct 19, 2010)

Lily said:


> That's very clear on why the diameter of the pin should be 0.265-2*0.005. However, is the sign before the 0.005 a plus? if yes, is it possible to have a minus instead? and what would it mean? Thanks!


The sign (looks like a plus) is a symbol for positional tolerance. It means the hole can move radially in any direction by .005 Since the hole can move .005 one way and the pin .005 the opposite way (worst case), then you would have to subtract 2*.005 off the pin size.


----------



## Shaggy (Oct 19, 2010)

It actually means the hole can move anywhere within a DIAMETER of .005 centered on the true position of the hole. True position meaning the perfect or exact dimensioned location of the hole. The little box is called a feature control frame. The ABC is the datum references and their order of significance. The hole location dimensions must have a box around them indicating they are "basic". The gist this type of dimensioning is that the locational tolerance is not driven by the locating dimensions (that is why they are basic). The location is driven by the feature control frame. In your case the hole can move such that the center falls within a .005 diameter zone centered upon the ideal center.

Wikipedia has some good info:

http://en.wikipedia.org/wiki/Geometric_dim...and_tolerancing


----------

