fixed fastener calculation

[AndrewTT]

Attached is a fixed fastener question from a GD&T textbook. I am interested to see what answers this group can come up with.

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The part with the clearance holes (part 1) assembles on top of the part with the tapped holes (part 2) and is fastened with cap screws. Allow a tolerance of at least .030 on both the threaded and clearance holes, use zero positional tolerance, and specify projected tolerance zones.
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fixed fastener formula
H = F + t1 + t2

Givens:
clearance hole LMC
zero positional tolerance for clearance hole (t1)
fastener size (F = 3/8, .375)

Find:
clearance hole MMC (H)
threaded hole positional tolerance (t2)

While there are many possible answers I am interested in using all of the available tolerance (leave no meat on the bone). What is the optimal answer?

 

[JNieman]

Apologies for adding some extra nonstandard shorthand John-Paul assumed correctly.

 

[3DDave]

JNieman,

At least it's not Indian notation where the digits are separated into non-uniform groups.

"They call 1,00,000 a lakh and 1,00,00,000 a crore."

http://mathforum.org/library/drmath/view/63335.html

AndrewTT,

The textbook is providing a canned method so the students don't have to think about what they are doing, just find or recall a matching formula given the missing pieces and plug-and-chug.

In Y14.5, they go about it the way I described, where one has a fixed fastener and knows the production tolerances for locating the features. This sets the minimum size for the mating hole.

I dislike the formula methods because if the users don't know enough arithmetic and geometry to derive the formulas for themselves they should probably not be doing the task. If they can derive it they won't make an error in recalling a formula at some later time.

I can't think of a time when the LMC of a hole was a critical, known fact and it was necessary to walk back what MMC value would come from it.


Here's the more interesting kind of question - for the calculated MMC and location tolerances what is the greatest forced offset between the surface used as B and the surface used as E? What is the greatest offset that can be allowed? In both cases, assume all the external surfaces are perfectly flat and perfectly oriented as shown and that the offset is only for parallel translation and does not include any rotation.

 

[JNieman]

@3DDave - learned something new today. Never saw Indian notation. And here I thought working between Imperial/Standard and Metric was rough