need help with giving dimensional tolerances

[dhyperman]

I need to get some instruction or advice on the best and easiest way to give dimensional tolerances. Maybe some good web site or something it is driving me crazy and holding me back.

Case where you have say a row of fingers and slots in a "comb". The slots and the finger have a tolerances, and the overall length has a tolerance also. and the small ones all add cant be more than the overall and its tolerance. But i need some help on giving the rest of it

 

[mog69]

dhyperman
The first and best reference I ever had was BS 308 - I think it's now part 2 of the Standard that covers dimensioning and the effects of cumulative tolerances. As you say in your example, you can't have the cumulative sum of tolerances within a feature exceeding the overall tolerance of that same feature. You have to make the judgment (based on priority of function) which is the most important - the individual elements or the overall. There are so many different ways of detailing the dimensions and their tolerances, the final decision has to be yours. You could try looking at similar drawings already created within your Company to see how others have resolved the question. There might be a Company “customs and practice” in place that says “this is how we want it done” but more likely the answer will be evident when you look at the essential function of the component and how it interacts with other mating components. Sorry - no easy answer !

 

[metalonis]

You might try posting this in the Drafting Standards & GD&T forum. It could prove an interesting subject for discussion.

 

[Darken99]

If I have 5 objects at 1" spacing on Center, the dimension I would use is:

<- (4) EQ. SPCS @ 1" = 4" ->

We use 1/16" as our tolerance on all parts unless otherwise stated. That means there is a 1/16" tolerance on the 4" total distance and a 1/16" tolerance on each 1" space.

 

[TomGDandT]

Consider the function of each feature.
This is a basic of GD&T.

 

[SLemin]

Darken,

you would end up with a tolerance clash if you used that, you'd need a tolerance of 1/4" on the 4" total distance, and 1/16" on each of the 1" spaces....

 

[ivymike]

how about calling out a "profile of a line" tolerance on the whole shape?

 

[scastillo]

In addition I would suggest sitting down with the machinist responsible for making the part and explaining exactly what you want the final product to be. As mog69 said, there are many ways of detailing a drawing, and for every way there is one for interpreting it.

A quick 5 minute chat would go a *long* way towards ensuring he is picking up what you are throwin' down.