GD&T and "Fixed Fastener formula" (ASME Y14.5)

D

dhavalvp

#1
Hi all
I have a doubt regarding the allocation of the positional tolerance using "Fixed Fastener Formula" mentioned in the ASME Y14.5.
The formula says that the allowable tolerance i.e. difference between the MMC of the fastener and the MMC of the hole is being equally divided and allocated to the clearabce part and the threaded part.
But I have seen some example in which the division of the tolerance is not equal i.e. not 50:50 but the division may be 60:40 or 70:30 i.e 60% of the total allowable tolerance is given to the threaded part and 40% is given to the clearence part.
Is there any guidelines that can be used for such unequal division of the tolerance or it comes from the experience only?
 
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Stijloor

Staff member
Super Moderator
#2
Re: GD&T and "Fixed FAstener formula"

Hi all
I have a doubt regarding the allocation of the positional tolerance using "Fixed Fastener Formula" mentioned in the ASME Y14.5.
The formula says that the allowable tolerance i.e. difference between the MMC of the fastener and the MMC of the hole is being equally divided and allocated to the clearabce part and the threaded part.
But I have seen some example in which the division of the tolerance is not equal i.e. not 50:50 but the division may be 60:40 or 70:30 i.e 60% of the total allowable tolerance is given to the threaded part and 40% is given to the clearence part.
Is there any guidelines that can be used for such unequal division of the tolerance or it comes from the experience only?
Hello dhavalvp! Welcome to The Cove Forums :bigwave: :bigwave:

There is no "standard" that states how to allocate the available tolerance.

It is a well-known fact that the location of threaded holes is more difficult to control that simple through holes. So experience with the variation on hole locations will be your best guide.

A 60-40 and 70-30 allocation has worked well.

Good luck.

Stijloor.
 
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