positional tolerance decimal equivalency.

[TOOLS4FOOLS]

Decimal equivalency. This is not about metric values and the order of magnitude.

This is about inches and its decimal equivalency in regards to hole size and positional tolerance.
If you have to I’ll state using ASME Y14.5 2009.

Does anyone practice or does it matter? By matter I mean “what is your/companies preference”?
Do the decimal places on the hole size need to must match its positional tolerance decimal place?
Can the tolerance on the hole size be larger than the positional tolerance or the tolerance on the hole
is equal to or less than the positional tolerance?

 

[KENAT]

TOOLS4FOOLS

1) Yes the hole size tolerance can be bigger than the position tolerance - hence the concept of 0 position tolerance @ MMC where all location variation is controlled by the size tolerance. Arguably use of 0 position actually gives the manufacturer the most flexibility & greatest potential to make good parts. Section 5.3.3 of 94 version explains this - figure 5-10 shows it.

2) Not sure about 2009 but ASME Y14.5M-1994 section 2.3.2 explicitly says "The basic dimension value is expressed with the same number of decimal places as the tolerance" this is essentially an extrapolation of the principles given earlier in section 2.3.2 for +- dimensions.

So for position the locating basic dimensions must match the number of decimals, but doesn't say that the feature size tolerance necessarily has to.



Remember too if appropriate you can override the block tolerance by directly tolerancing the size dimension. So fundamentally the number of decimals doesn't imply any specific tolerance - it's the application of the block tolerance based on number of decimals that does this.

Posting guidelines faq731-376

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

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

 

[ewh]

2) Y14.5-2009 ¶2.3.2(d): "Where basic dimensions are used, associated tolerances contain the number of decimal places necessary for control. There is no requirement for the basic dimension value to be expressed with the same number of decimal places as the tolerance."

"Know the rules well, so you can break them effectively."
-Dalai Lama XIV

 

[djhurayt]

Without quoting passages from the Y14.5 bible, doesn't the answer to this question simply boil down to either can be either as they are two different measurements.
One is a tolerance on the size of the hole.
The other is a tolerance on how accurately the hole is located.

Not the norm situation but I may not care how big the hole end up being so I give it a ±0.X
Were as I might need it be located perfectly or as perfectly as possible so I may give position tolerance of ±0.XXXXXXX...

 

[pmarc]

Can I hijack this discussion a little bit?

As I grew up in a metric part of the world, I still have difficulties to really understand why something like this, for example, is not allowed per Y14.5 on inch drawing:
.45[±].005

Could someone explain this to me?

P.S. This is not a tricky question. I really want to learn something here.

Thank you.

 

[KENAT]

"Y14.5M-1994 2.3.2 (b) Where bilateral tolerancing is used, both the plus and minus values and the dimension have the same number of decimal places." would be the simple 'because it says so' response.

It might be because prior to using decimal inch perhaps fractions were more common so it was done to try and make it clearer. I was wondering if it was to help make the distinction between metric & inch more obvious but I don't think that's it since:

"Y14.5M-1994 2.3.2 (b) Where bilateral tolerancing is used, both the plus and minus values have the same number of decimal places, using zeros where necessary."

For this I can understand it might be concern of folks 'jumping' a decimal place especially on a poor copy of a drawing or something.

However, fundamentally I don't know.

Posting guidelines faq731-376

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

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

 

[TOOLS4FOOLS]

Hello all. I have found my answers from this post. I think the replies are great. Thank you.