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Stack up analysis and Shim calculation

Stack up analysis and Shim calculation

Stack up analysis and Shim calculation

(OP)
hello all,

I've just done an axial stack up analysis for a loop in an assembly of 7 components.  As a result,
The calculated shim thickness is .001+/- .009.  
The questions is that do I need to modify some components' dimensions so that I can get a realistic shim thickness of at least .009 +/- .009 ?
Thanks for your help.

Sincerely,
lagump
HiPress Inc.

RE: Stack up analysis and Shim calculation

i expect that your tolerance bands aren't equally spread over the nominal dimn.

and i don't think you've allowed a sufficient +ve gapping to create a +ve shim ... ie one element in your stack up should be "shim allowance.

RE: Stack up analysis and Shim calculation

(OP)
Hi rb1957,

Thanks for your response.

Actually the tolerance bands are equally spread over the nominal dimensions which are +/- .001.  In the loop, there are requirements of one interference of .0005 and a gap of .030.

What do you meant by "sufficient gapping" to create a shim and "shim allowance" for one element in my stack up?  Please help to explain.

Thank you very much.

lagpump

RE: Stack up analysis and Shim calculation

it sounds odd to me to have both interference and gapping in a stack up ... either you can understand (physically) but both together ??.  maybe you mean that the stack up can have 0.005" interference or 0.03" gapping ??

a shim allowance would be a layer in your stack designed to be a shim, so that with nominal dimns it might be 0.02" thick but it could be 0.03" or 0.01", depending on your tolerancing.  so you'd define it as a 0.03" thick peelable shim or maybe as a "shim, thickness TBD"

RE: Stack up analysis and Shim calculation

Because you have seven components in your stackup and not all components will be at your maximum or minimum tolerance at the same time, I suggest you perform root sum square on your positive and minus tolerances.  You may find the attached excel file helpful.

In addition, you may want to consider laminated shim stock

RE: Stack up analysis and Shim calculation

I agree with rb1957.  Design in a nominal thickness shim pack.  Take .010" off of one of your parts and replace it with a shim pack that can vary between 0 and .020".  This could be a stack of .001" shims... or some .005"s and .010"s.

-Dustin
Professional Engineer
Pretty good with SolidWorks

RE: Stack up analysis and Shim calculation

(OP)
Thank you all for your suggestions!

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