Stack up Tolerance Analysis.

[rmaki]

What is the calculation needed to do a Stack up Tolerance
Analysis.Never done it before.
I have a part in a "U" shape with a hole pattern of 20 holes
and a couple of slot on the sides.
Tolerance is off by .001" in one side of the hole pateern and on one slot.
Any ideas?
Thank you.

 

[KENAT]

thread1103-229607
thread1103-139353
thread2-188871

Simplistically you add all the contributing dimensions and the tolerances to get the overal dimension and tolerance.

If the above links don't help come back with a diagram of your particular situation and someone may be able to give a more targetted respons.

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[drawoh]

rmaki,

Tolerance off by only .001"? Sounds like a pretty accurate hole pattern to me!

Tolerance stack up is an assembly analysis for evaluating tolerances on your drawings. It is a useful process for designers and design checkers. It sounds like you are doing inspection. What do you want to accomplish?

If you insist on your screws and bolts passing through clearance holes without interference, check out the appendices of ASME Y14.5. My website at

http://home.eol.ca/~hgibson/tolerances,

covers some non-GD&T techniques, especially helpful if you were not the one who generated the drawings.

If you need to position components, you need to do algebra and arithmetic and then add and subtract tolerances.

If you have chain dimensions on a single part, you can do a stack-up analysis, or you can re-draw the part and apply tolerances correctly.

JHG

 

[rmaki]

Thanks for the reply.
Drawoh, all the holes on the left side are off (10)plus one slot.
Looks like the set up was move on the CNC operation.

 

[desertfox]

Hi rmaki

What is the allowable tolerance for the holes to be off nominal?
To do a tolerance stack you need all the relevant drawings which fit into the particular assembly, then you put the tolerances on each component max or min and assuming the components are made to max and min check wether the assembly can still go together.
What I usually do is mark up a print in red of the assembly with max and min dimensions as this helps me visulise what I am checking.
To be honest tolerance stacking should be done as part of checking drawings before parts go for manufacture and should be as mandatory as putting dimensions on drawings.

desertfox

 

[KENAT]

To be honest tolerance stacking should be done as part of checking drawings before parts go for manufacture and should be as mandatory as putting dimensions on drawings.

Go on desertfox, tell another one, I needed a good laugh.

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[desertfox]

Hi Kenat

Glad it made you laugh, I said it tongue in cheek but I meant it lol.

 

[rmaki]

Tolerance is +/-.0005".

 

[desertfox]

Hi rmaki

So the parts out of tolerance and therefore should be rejected, however what are the holes for and what does the part actually do? can you upload a drawing of the part?
If you can provide more information then we might be able to help further.

desertfox

 

[rmaki]

Sorry, no DWG.
The holes are mounting holes.

 

[desertfox]

Hi rmaki

What are the holes for dowels, bolts, screws ? if there for bolts then the 0.001" tol is a nonsense, can you but more explicit.

desertfox

 

[rmaki]

Believe me, makes perfect sense it is for a Navy program.
More like a press fit,mounting holes.

 

[desertfox]

Hi rmaki

Okay so how would you like us to help you.

desertfox

 

[rmaki]

We want to establish the proper approach for the repair (we still don't know if it's allowed).
It's seems that the holes are shift unilaterally may be .0002" to .0003" on the x axis.

 

[desertfox]

Hi rmaki

With the information you have provided so far it would be easier extracting teeth from a sabre tooth tiger and there extinct.

desertfox

 

[KENAT]

Easy there. If rmaki needs more help lets assume they'll ask and that otherwise the information given in the first few posts is enough to get them thinking.

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[drawoh]

We want to establish the proper approach for the repair (we still don't know if it's allowed).
It's seems that the holes are shift unilaterally may be .0002" to .0003" on the x axis.

We do not understand what your assembly has to do. If you have a component that must be located within Ø.001", your part is scrap. If the drafter ought to be horsewhipped and bludgeoned as per TheTick's recommendations in some other posts, you can review the actual design requirement and update your tolerances to something looser than what you fabricated.

Is your organization the fabricator or the designer?

JHG

 

[desertfox]

Hang on

First time he was saying holes are off by 0.001" and tol was .0005", now he is saying holes off by 0.0002" to 0.0003"
so now the holes are in tol?????????????.
Unless you can provide some more information we cannot help you further as the information you have given so far is insufficient

desertfox

 

[ctopher]

Maki,
Can you please post a sketch of your design intent?

Chris
SolidWorks 09 SP4.1
ctopher's home
SolidWorks Legion

 

[NormCrawford]

rmaki,
Are you really asking how to stack the allowable position tolerance of a hole with the allowable datum shift? That woud be a more explicit question then simply asking how to do tolerance analysis in general.
Tolerance analysis can be a feature to feature analysis, an allowable location like it sounds like you are asking, upwards to an entire assembly of components.

I think this is why some of the replies are a bit on the humpor side. But if you are just wanting to know how to stack allowable tolerance on a feature based off of datum features of size specified at mmc, there is an answer. Unfortunately, way difficult to explain in this forum for a "pattern" of features of size. For a single feature, not so difficult, but for a pattern? I have found only 1 software application that can verifiably do that right and its no spreadsheet. And there are CMMs that when correctly programmed that can do it. But in an open set-up? Go to functional gaging.

Norm

Norm Crawford
GDTP-S
Applied Geometrics, Inc.

http://www.GDandT.com