Determining Position Tolerance Value
Determining Position Tolerance Value
(OP)
Hello,
I understand most GD&T and how to interpret a position callout, however, I'm still a little confused on how to actually determine the correct value for diametrical position callouts.
Please let me know if my below method is correct:
1. Two parts are to be bolted together via a pattern of 4 .25-28 UNF-2B bolts.
2. From online tables, I have determined the correct close-fit clearance hole to be .266 +.006/-.001 (.265 to .272).
3. From this, subtract the bolt major diameter from the smallest hole: .265 - .250 = .015
4. Therefore, I have .015 tolerance to split between the two 4-bolt patterns (.010 and .005 or .007 and .008 for example)
I feel like this is too simple. Does the threaded hole not come into play at all?
What book and or website do you guys use/recommend as a good resource for GD&T?
Any help is much appreciated.
Thanks!
I understand most GD&T and how to interpret a position callout, however, I'm still a little confused on how to actually determine the correct value for diametrical position callouts.
Please let me know if my below method is correct:
1. Two parts are to be bolted together via a pattern of 4 .25-28 UNF-2B bolts.
2. From online tables, I have determined the correct close-fit clearance hole to be .266 +.006/-.001 (.265 to .272).
3. From this, subtract the bolt major diameter from the smallest hole: .265 - .250 = .015
4. Therefore, I have .015 tolerance to split between the two 4-bolt patterns (.010 and .005 or .007 and .008 for example)
I feel like this is too simple. Does the threaded hole not come into play at all?
What book and or website do you guys use/recommend as a good resource for GD&T?
Any help is much appreciated.
Thanks!





RE: Determining Position Tolerance Value
It also gives guidance on projected tolerance or over-sizing the hole in lieu.
I suggest you take a look at the proverbial 'horses mouth'.
BTW, I'd think twice putting much less than a .010 tolerance on a threaded hole - it's often better to split the tolerance allowance with a bit more going to the threaded hole than the clearance hole due to typical process capabilities for threaded V plain holes.
The typical 'close fit' holes may be more applicable for floating fastener than fixed fastener so take them with a pinch of salt as they can lead to unnecessarily tight position tolerances.
(*Be careful there's a bit of an error on a tab relating to converting +- dims to pos tol.)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Determining Position Tolerance Value
Season
RE: Determining Position Tolerance Value
RE: Determining Position Tolerance Value
If the projected tolerance zone concept is not used, possible orientation error of the threaded holes relative to mating face needs to be taken into account - and this is where additional threaded hole parameter, that is ,the minimum depth of engagement of threaded member comes into play. The formula in Appendix B.5 of Y14.5-2009 shows how it is done.