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Tolerance analysis (hole and peg)

Tolerance analysis (hole and peg)

Tolerance analysis (hole and peg)

(OP)
Hi all,
I need to analyze tolerance for fit of two parts. I need to do this type of analysis with two sets of features:
FEATURE 1
One part has 3 pegs (120deg apart) and the other has holes. How do I calculate X directional shift of these two parts?

Here is what I did, let me know if this is correct:
Gap 1 = (Hole1-Peg1)/2
Gap 2 =....
Gap 3 =....

Xtol= min(gap1,gap2,gap3)

I did this because, the part can shift horiztonally while limited by the minimum allowable gap. But I dont feel this is the right way to do it.

Reason being, there is no consideration for the horiztonal shift occuring from the rotation of one part within the other.

No consideration for the combination of rotational and linear components of shift.

FEATURE 2
This is slightly more complicated. The features that engage with each other are still 3, and are at 120deg. However they are not pegs and holes.

They are trenches and pillars with a taper on each other. Here is am concerned about the following:

1. How the tolerance on the 120deg angle affects the fit along the axis.
2. How the individual rotation of these features affect the lateral shift.
3. How the individual rotation of these features affect the fit along the axis.
4. And lastly how the normal of these two parts end up (or the angle between these two parts).

If the second set of questions are more complicated, atleast any attempts at answering the first portion of my post would still be a lot of help.

Thanks in advance and sorry for the long post.


 

RE: Tolerance analysis (hole and peg)

If I understand correctly, and you are using GD&T, then for the first part the calculations given in appendix B of ASME Y14.5M-1994 or equivalent should do the trick for you.

If not using GD&T, you can translate the 'circle' to +- by calculating the inscribed square.

thread1103-221602: Appendix B4 ASME Y14.5M-1994 Fixed Fastener Positional Tolerance Calc. 4 Sep 08 3:26 post has a spreadsheet with examples.

Posting guidelines FAQ731-376: Eng-Tips.com Forum Policies http://eng-tips.com/market.cfm? (probably not aimed specifically at you)
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?

RE: Tolerance analysis (hole and peg)

Is there any chance you could post a sketch with the dimensioning and tolerancing scheme you used for the calculation in CASE 1?

RE: Tolerance analysis (hole and peg)

(OP)
KENAT, I will try out the suggestions in the post and let you know. Thanks.

pmarc, there is no sketch or tolerancing yet, I just have a solid model of the features I described. Did you want to see the solid model? Thanks.

RE: Tolerance analysis (hole and peg)

I was rather curious whether you are using coordinate dimensioning metod or applying GD&T. Solid model is not necessary since I believe I am imagining the situation correctly.

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