Tolerance question 2

[aero101]

I recently came across the drawing with 2 decimal tolerance on 3 decimal dimension, eg: .567 +/-.01,it is a machine part, I can't see the logic having 2 decimal tolerance here, am I missing something? (the tolerances specified on drawing are .XX +/-.05 and .XXX +/-.005), thank you for your input

 

[Belanger]

It looks like you're using inches on these numbers, so we can look up the rules in ASME Y14.5, paragraph 2.3.2:

"Where bilateral tolerancing is used, both the plus and minus values and the dimension have the same number of decimal places."

So you're right; they should have stated .567 ± .010.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[aero101]

Hello Belanger, Thank you for the confirmation.

 

[aero101]

Also wanted to ask -the ASME quote - does this need to be purchased or is it free info the ASME standars, thanks again

 

[PeterStock]

Your company should have or should purchase a copy. Our clint has a account with IHS (

http://www.ihs.com)

where you can find a large number of standards including all versions of ASME Y14.5.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[aero101]

currently not part of any company, so the best is to set up account with ASME or IHS? what is the cheapest way to go? thank you

 

[Belanger]

I don't know if IHS has a deal where you can access many standards for one bulk price, but you can always order the specific standards from

http://www.asme.org.

FYI -- They ain't cheap! For either the PDF version or the traditional paperback version, the Y14.5 standard is $170.

Which makes me think of another question for the group: Has anyone else noticed the PDF version for real cheap on eBay? It's like 29 bucks -- are those illegal Chinese knockoffs?

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[PeterStock]

Probably a pirate copy of some kind.

Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services

http://www.infotechpr.net

 

[SeasonLee]

Belanger

May I ask : same number of decimal places you referred to is standard Y14.5 1994 or 2009 version, its true for 1994 version, I am not quite sure are there any changes in 2009 version, I don’t have 2009 standard on hand.

But, I know there is a change on feature control frame callout in 2009 version, geometric tolerances and the basic dimensions may have unequal decimal places. For example :

POS|Ø.010 circle M|A|B|C-----1994 version
POS|Ø.01 circle M|A|B|C-----2009 version

SeasonLee

 

[Belanger]

Yes, Season, I see that in 2009 the basic dim doesn't have to have the same number of decimal places as the geometric tolerance. I don't think I ever noticed that.

I see that the 2009 edition didn't change the rule for ± tolerances, though.

John-Paul Belanger
Certified Sr. GD&T Professional
Geometric Learning Systems

 

[aero101]

but is there a point to have 567 ± .01?

 

[KENAT]

It should be .567+-.010.

There may be a good reason to have 567+-.010. Without knowing the application it's not possible to say. You can't just use rules of thumb that 'if it has a significant figure at the third decimal it must need a tight tolerance' or similar.

I'll sometimes do a 3 place decimal conversion of a fractional size, say .375 for 3/8, however may only need +-.010 or even looser on it functionally and will specify that.

Posting guidelines faq731-376

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

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

 

[MintJulep]

but is there a point to have .567 ± .01?

The designer had determined that the part won't function correctly if that feature is smaller than .557 or larger than .577.

 

[aero101]

MintJulep
This is what I would understand if the dim callout says .567+/- .010, but does .567 +/- .01 really imply .557 to .577 and not .55X o 57X?

 

[aero101]

or actually does not .567 +/-.01 imply that the tolerance is .55 to .57?

 

[MintJulep]

.567-.01=.557.

.567+.01=.577

 

[KENAT]

aero, while the callout is wrong to 14.5-94 and probably other 14.5 editions, I believe most people would accept the principle(al?) of infinite trailing zeros applies. There is no rounding when it comes to tolerance like this.

However, the fact this is causing confusion shows one reason for the rule in the first place which hadn't really occurred to me before.

Posting guidelines faq731-376

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

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

 

[fsincox]

Seasonlee,
Thank you, I had not noticed that change yet either.
Frank

 

[MintJulep]

Where bilateral tolerancing is used, both the plus and minus values and the dimension have the same number of decimal places.

Not:

"shall have the same number of decimal places"

"should be shown with the same number of decimal places"

"must be written with the same number of decimal places.

It's

"have the same number of decimal places"

Shown or not, assume that the insignificant trailing zeros are there and do the arithmetic.