Precision

[sshosseinee]

Hi, what is the difference between these two?
2H13
2.0H13
Does this influence manufacturing process? Is there a difference in control process?
Thanks.

 

[Burunduk]

No difference, except the second option is not a valid way to specify a metric dimension.
"Where the dimension is a whole number, neither the decimal point nor a zero shall be shown" (ASME Y14.5).

 

[3DDave]

I doubt that Y14.5 covers such tolerance class specifications. Those are typically ISO standards - see

https://www.eng-tips.com/viewthread.cfm?qid=323388

for a discussion of same.

 

[Burunduk]

Y14.5 mentions the system of limits and fits and provides examples. See "metric limits and fits" in Y14.5, any of the more recent versions. It also references ANSI B4.2 which covers this subject in detail.

Regardless, specifying a tolerance class doesn't override the rules of metric dimensioning covered by Y14.5, or the Y14.5 rule that states that all dimensions and tolerances are treated as absolute - as if they were followed by infinite zeros after the last digit, regardless of the number of digits shown.

 

[3DDave]

OK - so B4.2 copies the ISO. Great to know. Also that is referenced, not used, in Y14.5, so Y14.5 literally doesn't cover it.

A callout of 2.4H13 would be acceptable.

"Cover" to exhaustively provide all details required to understand the full extent, if you need to know what I mean by that term.

 

[Burunduk]

2.4H13 is indeed acceptable.
2.0H13 is not, because of the rules covered by Y14.5 - and not by B4.2 or the equivalent ISO 286. Hope this clarifies the point.

 

[3DDave]

It is insufficient, as not all callouts for fits are on drawings created in accordance with Y14.5. The referencing document should directly specify the document that tells what the "H" stands for rather than making the user dig through multiple layers to find that out.

I hope you don't continue to say that 14.5 is the Holiest of Holy Books when it literally doesn't explain how this tolerancing system works.

 

[Daren Samy]

2.0H13 is wrong way of expressing fit

Daren!

 

[Burunduk]

The referencing document should directly specify the document that tells what the "H" stands for rather than making the user dig through multiple layers to find that out

It does.
See 5.2.1 in Y14.5-2018, or 2.2.1 in Y14.5-2009.
It tells you about the "basic size" and "tolerance symbol", directs you to an example figure, and tells you to "See ANSI B4.2 for complete information on this system."
What multiple layers?
Y14.5 has many flaws but I don't see one here.

 

[3DDave]

Burunduk,

I didn't say there was a flaw - you have. Why?

"The document" in question isn't Y14.5. It is the drawing or specification that includes this shortcut as a requirement that should specify the appropriate tolerance specification directly.

Specifying only Y14.5 adds an additional layer to read through to find the tolerance requirement. That additional layer to finding out what the requirement is by playing "match the picture" (the paragraphs you mentioned say nothing about the way the tolerance is presented)and then backing up to the referenced paragraph "See ..."

The reference in Y14.5 adds no actionable information to the user of the limits and fits standard. It manages to not even show how it would be applied to a drawing as a dimensional control.

You are smart enough to know all this, so I'll put it down to being argumentative. Oh, you can reply that I am the same, so I've saved that effort.

 

[Wuzhee]

Hi, what is the difference between these two?
2H13
2.0H13

The only explanation I could imagine is some inch guy tried to force their decimals onto the metric guys. Because why would anyone want clear drawings where you can write .00005 +.00012/-.00000 instead? Who the hell understands +0.1/0?
Decimals rule and you should add as many as possible!

 

[Burunduk]

3DDave,
I know we are argumentative, but I honestly didn't get that the "referencing document" is the drawing. We were talking about the fact that Y14.5 references B4.2 and has some information on limits and fits, so it wasn't clear to me what you were saying.

So you are saying the drawing should reference the limits and fits standard.
Actually, I don't think I ever encountered a drawing that references either ANSI B4.2 or ISO 286. There are so many tables, conversion charts, free online calculators, internal company documents, engineering handbooks etc. that I think almost no one looks at the actual ISO/ANSI standards anymore, for selection of metric hole-shaft fits and interpretation of tolerance class designations. I may be one of the few exceptions as I use the ANSI B4.2-1978 document.
For what it's worth, B4.2 doesn't include a "reference to this standard" requirement.

I didn't say there was a flaw - you have. Why?

Here is where you suggested a flaw in Y14.5:

I hope you don't continue to say that 14.5 is the Holiest of Holy Books when it literally doesn't explain how this tolerancing system works.

Well, it's not Y14.5's job and you're smart enough to know it.
Yeah, you know what's next... "argumentative".

 

[Burunduk]

Because why would anyone want clear drawings where you can write .005 +.00012/-.000000 instead?

Wuzhee, you can't do it like this.
The number of decimals shall be identical for the dimension value, and the plus and minus values. You're missing 2 decimals for the dimension and have an extra decimal for the minus limit value. The inch guys won't like it.

 

[Wuzhee]

Corrected for historical purposes.

 

[Burunduk]

Wuzhee,
I'm sorry to tell you, but it looks like you won't be accepted to the inch guys club after all. See, .00005 +.00012/-.00000 is unconvincing. You specified a tolerance more than twice larger than the dimension itself. Legal, but impractical .