I'm helping my stepson with his homework for his Blueprint Reading class. There's a question regarding the tolerances on the print.
The tolerances on the print reads:
"Decimal" "xxx +/- .010" "+/- xx +/- .020"
Never having taken any similar classes, I don't understand why there are multiple tolerances listed?
The actual question he has to answer is : "What is the significance of the tolerance xx +/- .020?"
Thanks! :
Good heavens, I didn't know they taught that anymore! What level are we talking about? Beginner or advanced?
You should have a nominal dimension with a basic tolerance. Like 1.250" +/- .010. This means the finished part has to measure between 1.260 and 1.240, and thus a total of .020" allowance.
Is there a process described the part will go through? I don't think they do this but maybe they are calling out different tolerances for different steps in the process.
If you have a symbol along with the basic dimension like one of these:
along with the additional tolerances, that tolerance goes for that feature depicted by the symbol.
Does that make sense?
I think you meant to write:
"Decimal" "xxx +/- .010" "xx +/- .020"
What is meant by the quotes above is this:
Dimensions on the print which are carried to three decimal places get a tolerance of +/- .010. Dimensions on the print which are carried to two decimal places get a tolerance of +/- .020.
That part is simple.
I honestly don't know what he is trying to ask with the question "What is the significance of the tolerance xx +/- .020?"
The answer might be as simple as "Dimensions on the print which are carried to two decimal places get a tolerance of +/- .020." but his use of the word "significance" makes it sound like he's after something more complicated.
Awesome, that's the info we needed!
He's going to the local community college to get his welding certificate, and blueprint reading is a required class.
JamesMcD wrote: I think you meant to write: "Decimal" "xxx +/- .010" "xx +/- .020" What is meant by the quotes above is this: Dimensions on the print which are carried to three decimal places get a tolerance of +/- .010. Dimensions on the print which are carried to two decimal places get a tolerance of +/- .020. That part is simple. I honestly don't know what he is trying to ask with the question "What is the significance of the tolerance xx +/- .020?" The answer might be as simple as "Dimensions on the print which are carried to two decimal places get a tolerance of +/- .020." but his use of the word "significance" makes it sound like he's after something more complicated.
I agree with this analysis. The wording is strange, if you had an actual scan of the dimension and title block, it would be easier to figure out what the question is.
This is the important part of the post.
Dimensions on the print which are carried to three decimal places get a tolerance of +/- .010. Dimensions on the print which are carried to two decimal places get a tolerance of +/- .020.
In reply to JamesMcD:
I also agree - this is what I was taught.
Tolerance written in the notes saves the designer from putting +/- .010 on every dimension.
You will also see "Unless Otherwise Specified" in that block. If it doesn't have a dimension, UOS applies. Mostly used for radii and fillets.
Dan
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