I'm working on a tolerance stack an

[Buck61]

I'm working on a tolerance stack analysis to determine the minimum GAP in vertical direction between the BEZEL and CASTING via four parts in assembly shown in attached drawing.

A Summary of two issues I’ve encountered (details in items 1 & 2 below):
-How to perform a loop analysis to calculate the GAP to include the revised lower limit tolerance of HOUSING dimension 4.71" ± .03" without bypassing the CASTING’s contribution
to the Tol stack analysis. Also there appears to be no direct loop (path) from the 4.71" ± .03" dim to the CASTING or GASKET that follows Tol Stackup rules.
-Three of the four parts mate at a 20 degree angle.

I am using James Meadows' "Tolerance Stack-Up Analysis 2nd Ed" for guidance but nowhere does it address this type of problem.

1. Referring to Detail B, starting at the bottom of the GAP where down is (-) and up (+), dimension A1 1.399 is where I encounter the first instance of the angled interface between the CASTING & GASKET where each part dimension contributing to the tol stack is at 20 degree angle and not in vertical direction needed to continue the loop analysis thru the assembly back to the top of the GAP. My 1st approach shown is to dimension the CASTING & GASKET dimensions A1, A2, & B dimensions at 20 degrees and then trig out the respective vertical dimension for each. This approach however does not appear to be a correct & cumbersome. Only other option seems to be to add a vertical dimension from horizontal Top edge of the casting (Detail B & C) to a point at the base of the CASTING’s IPX2 seal bead shown in Detail B.

2. The loop analysis must include the effect of tolerance +/- .03" from the 4.71" ± .03" HOUSING dimension shown in Section A-A, which replaces the original limit dimension 4.74"/4.71". LMC is now 4.68". This change to open up lower tolerance is why I need to calculate the GAP to determine if any interference exists between the BEZEL and CASTING at LMC.
I am not sure what dimension feature to use from the GASKET to the HOUSING to transition back to the vertical direction. C1 dimension is simply projected perpendicular from a point at the top of the CASTING’s IPX2 seal bead to the top of the GASKET /HOUSING mating interface which again seems incorrect. However the C1 dimension appears the only path in the loop to ‘leave' the GASKET and move to the Top surface of the HOUSING (Detail B). Possible solution: Add ±.03 tolerance to ±.006 of C1 dimension shown in Detail B in place of 4.71 +/-.03" dimension tolerance (Section A-A)?

Two perceived problems if the 4.71" ± .03" HOUSING dimension is included in the loop analysis:
- No direct path from the Housing to the GASKET
- It will bypass the CASTING's contribution to the tol stack GAP.

Spinning my wheels...

Appreciate suggestions and/or any print or online media resources.

Thanks,
Buck

 

[3DDave]

Tolerance analysis is cumbersome.

If you have the models, adjust the dimensions to their limits and let the CAD package do the math.

Note that there is no default orientation tolerance given in your example and this will greatly affect the results.

 

[greenimi]

Maybe use a software analysis package....CeTol, Vis-VSA, etc. But those are not cheap nor easy to learn.

 

[Buck61]

Hi 3DDAve,
Thanks for your initial reply. TA is indeed cumbersome.
I'm not clear on your comment "....there is no default orientation tolerance given in your example and this will greatly affect the results."
Orientation tolerance, e.g., position? The individual part drawings all have GDT tolerancing which are not shown in this TA assy drawing. Do you mean applying orientation tol (position, etc.,) to assy? If so, where specifically would you apply GDT orientation in this assy?

Sorry if I am misinterpreting your comment.

Also appreciate any help per item 1 of my original post above. I can't find anywhere online how to work with dimensions at 20 degree angle (part dimensions in stackup are neither vertical or horizontal)and enter same in TA stackup worksheet. Otherwise from where and how do I continue the loop analysis thru the assembly back to the top of the "GAP".

Thanks again!
Buck

 

[Tarator]

Buck61,

It is very hard to follow without knowing the design, the assy, etc. Can you share the STEP file of the assy? I could take a look.

Could you not use cos 20º or 1 / cos 20° as a linear factor in your stack-up?