digits on basic dim and the tolerance 2

[nry67]

Hi somebody can help me to found the information concerning the precision of dim and tol. Value in mm.

I know it's possible to have : 4+/-0.2 or an other exemple 4.2+/-0.5
My question is, Is it possible to indicate on a drawing this exemple : 4.25+/-0.1

To me it's strange to use 2 digits on the dim and only 1 in the tolerance.

Thank you

 

[Burunduk]

(b) Where bilateral tolerancing is used, both the plus
and minus values shall have the same number of decimal places, using zeros where necessary. The dimension value
of 32 is not required to have the same number of decimal places as the tolerance values.

The portion in bold is the answer.
Note that it is applicable to any dimension, not just 32. Their example shows 32 and the text followed.

 

[nry67]

I'm not talking about the distribution of IT". My question concerns the fact of writing the BASIC DIMENSION with 2 digits after the dot and the tolerance only with 2. Example: 25.75 +/- 0.3. or a second example like the attached file .
For me this writing is not conceivable.
My question is, is there anything written about this somewhere?

 

[TheTick]

Basic dimensions are exact, ideal dimensions. They have no tolerance, therefore no tolerance or precision is implied by decimal places. Trailing zeroes are implied and infinite.

 

[3DDave]

Too many students got beaten up in science class about significant digits and then went to get beaten up in math class about rounding numbers and they take what they thought those beatings were about into drafting class. I've heard of people applying rounding to tolerances. +/-.1 = range +.14999/-.14999 because that's how rounding works.

While the inch dimensioning section has a clear rule, the millimeter dimensioning section makes a fuzzy implication about this.

'2018 5.3.1. Millimeter Dimensioning (d) Where basic dimensions are used, associated tolerances contain the number of decimal places necessary for the required level of precision.

vs.

'2018 5.3.2 Inc Dimensioning (d) ...There is no requirement for the basic dimension value to be expressed with the same number of decimal places as the tolerance.

Did I mention a problem in another thread, something along the lines of the number of rules? Yes, yes I did.

 

[nry67]

I'm sorry but I must be expressing myself badly.
I summarize.
On a drawing I have the information above.
My doubt is to write 25.75 and not 25.7 which for me is altogether more logical given that the value in the control frame is 0.6
Am I right in saying this?
I'm agree with 3DDave "the millimeter dimensioning section makes a fuzzy implication about this."

 

[3DDave]

It's not "more logical". The feature limits ought to be whatever they need to be. Adding another zero to the tolerance doesn't make it more precise.

 

[nry67]

Yes, I agree for the value of tolerance, but remove the second digit after the dot in the dimension, wouldn't that be fairer?

 

[Burunduk]

"fairer" in what sense?
If you reduce the value of the basic dimension by 0.05 you move the center of the 0.6 tolerance zone by 0.05 "down", which results in different limits for the feature. Decide what your design dimension should be, and specify it, including the last non-zero digit.

 

[nry67]

I would say that the 0.05 mm (5 hundredth) is not "serious" since the tolerance is at the tenth (0.6)

 

[BiPolarMoment]

Maybe you are tied up because by having a nominal that is defined to the hundredth then you must be able to measure to the hundredth, no matter that the tolerance is only to the tenth. Tough titties, you should be measuring with that much accuracy to have any confidence in measuring tenths near the limits of the tolerance anyway.

 

[Burunduk]

I would say that the 0.05 mm (5 hundredth) is not "serious" since the tolerance is at the tenth (0.6)

Then change the design dimension to 25.7.

 

[TheTick]

I would say that the 0.05 mm (5 hundredth) is not "serious" since the tolerance is at the tenth (0.6)

If you're making this determination based on the requirements of the design fit and function requirements, fine.

If you're making this determination because that 0.05mm "doesn't seem like a lot", you need to step away.

Honesty may be the best policy, but insanity is a better defense.

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[CheckerHater]

My question is, is there anything written about this somewhere?

It is written in:
ASME Y14.5M-1994 Para. 2.4
ASME Y14.5-2009 Para. 2.4
ASME Y14.5-2018 Para. 5.4

https://files.engineering.com/getfi...-831c-43cd-b182-63a8d74c2302&file=Capture.PNG

"For every expert there is an equal and opposite expert"
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[nry67]

It is written in:
ASME Y14.5M-1994 Para. 2.4
ASME Y14.5-2009 Para. 2.4
ASME Y14.5-2018 Para. 5.4

This explains to means the possibility (to think) to add a ZERO(S) after the last character.
My problem is not the number of ZERO, it's there is a value non-zero on second position after the dot on the Dimension and just one in the tolerance.

 

[nry67]

I will ask my question differently.
On a drawing there is this information.
15.236 +/- 0.1
Does this bother anyone?
Why indicate an accuracy of .236 on the dimension, when the tolerance requires .1

 

[CheckerHater]

Because there is no difference between 0.1 and 0.10000.
There are no trailing zeros on metric drawings.

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[CheckerHater]

Will it bother you to measure limits 15.336/15.136 because that's exactly what you will be measuring?

"For every expert there is an equal and opposite expert"
Arthur C. Clarke Profiles of the future

 

[BiPolarMoment]

In your example you still need to satisfy measuring the limits of 15.136 to 15.336... and measure it with confidence. You could also measure the limits 15.2-15.3 if that makes you feel better, and reject everything outside of that range regardless of if it is actually a good part.

 

[nry67]

][/quote]

To me there is a difference. +/- 0.1 can be inspected by a caliper and +/-0.10000 needs a control tool much more accurate. So more expensive.
And if I go in the direction, and I note as value on my coin 0.1003. What do I deduce from this? While it is not requested on the drawing.