Tolerance stack analysis

[BLUEHONDA]

Hello i am a little new to engineering and i have just been asked to do a tolerance stack analysis on a project i am working on.
Attched is a picture that shows a machined from solid chassis with two steps in it, on the top step PCB-2 is fixed and on the bottom step PCB-4 is fixed.
On the base of the box there is a raised section which PART-2 sits and terminates at the top toPCB-4, on the right of Part-2 is PART-2 this sits slightly lower in the chassis and its terminals are connect to PCB-4 through SPACER-3.
On the top face of PCB-2 and PCB-4 is another PCB (PCB-1 & PCB3) mounted on spacers (sopacer-1 and spacer 2)
.
Could sombody please show me an example of how to do a toleance stack on this.

Datum would be from the top of the chassis i think??
Chassis tolerance = +/-0.15
spacers +/- 0.1
part-2 +/- 0.2
part-1 +/- 0.25
pcb-1,2,3 & 4 +/- 0.3

Thank you, any help would be very much appresiated.

 

[monkeydog]

You do not have enough information to perform a tolerance analysis.

Try to perform a web search on tolerance analysis, where you will be able to see some examples.

 

[BLUEHONDA]

Hello monkeydog, I have tried searching for examples, but unable to find anything like what I'm trying to.
Could you please expand on what I have missing?? Like I said I am new to this stuff.
Thank you.

 

[BLUEHONDA]

Thank you Monkeydog, I have tried searching for examples but unable to find anything similar to what I'm trying to do. Would you please expand on what you think is missing?

Thank you.

 

[desertfox]

Whats mising is the overall dimensions of the components themselves, ie part 1 tol +/- 0.25 what are the dimensions of part 1.
You need to have detailed drawings of all the parts.

desertfox

 

[BLUEHONDA]

Sorry! Yes I am aware of that I purposely left them off, I'm looking for sombody to show me an example and thought it might be easier if they added there own dimension, but with the tolerances specified.
No engineering drawing have been produced yet, it's just a concept at this stage.

 

[desertfox]

Hi
We can't guess what the figures might be even for an example,for instance if you think PCB 4 will rest on the chassis and on spacer 3 which might hold part 1 to the chassis then think again.
We need to understand which components need to rest on what and whats important in terms of its relationship with the other components.

desertfox

 

[BLUEHONDA]

I have attached the same image with dimensions and tolerances on, part-1 will need to terminate to the underside of PCB-4 through spacer-3 and part-2 will terminate dierctly to the underside of PCB-4.
Parts 1 & 2 are fixed to the chassis base then, spacer-3 (metal m/f spacer) will be fitted to part-1, pcb-4 will then be fixed to the lower chassis step, then part-2 and spacer-3 will be secured from the top side of pcb-4 using screws, flat washer and wavey washers.

Hope this makes it more clear ?

Thank You.

 

[monkeydog]

Bluehonda,
Most anyone on this forum can perform the analysis for you, but that is not what this forum is about, nor what you asked.

I performed a web search, and third link down was this one:

http://adcats.et.byu.edu/Publication/87-5/WAM2.html

Is that example inadequate?

It seems to have the "how to instructions" you are looking for.

 

[BLUEHONDA]

Ok thank you very much for your help! Much appreciated.

 

[desertfox]

It won't work with the tolerances and dimensions you indicate, for instance Part2 can be 70.2 and the chassis it sits on can be 169.85 however this means the Part2 component sits proud above the ledge for PCB4 by about 0.5mm, so PCB 4 can't sit on the ledge because Part2 holds it off.

 

[KENAT]

Also, are you trying to do simple worst case, or RSS or a slightly more complex statistical analysis?

Drafting Standards, GD&T & Tolerance Analysis may be a better place for such questions in future.

Posting guidelines faq731-376

http://eng-tips.com/market.cfm?

(probably not aimed specifically at you)
What is Engineering anyway: faq1088-1484​

 

[BLUEHONDA]

Just a simple worst case, thank you all for your comments! Much appreciated.