Easy question

[gabimo]

I got the following question today:
ASME Y14.5-2009

Regular feature of size (pin) dimensioned as follows:

Case1: Ø.125±.003 (OD size dimension)

Case 2: basic diameter .125, and profile within .006

Can you indicate or imagine a scenario/case (how the pin should look like) that can be acceptable per one case, but not per the other?
In other words, how the form error, circularity, cylindricity, straightness, waiting, barreling will be affected by one case but not by the other.

 

[jassco]

Easy answer:

They are same unless you remove Rule no. from case #1.

Best regards,

Alex

 

[pylfrm]

gabimot,

The profile tolerance would accept a perfectly cylindrical pin of diameter .119 or .131, each of which would violate the size tolerance by a factor of 2.

The size tolerance would accept a curved pin of actual local size .122 and straightness error .006, which would violate the profile tolerance by a factor of 1.5.


pylfrm

 

[Belanger]

gabimot -- they are not the same at all because as pylfrm points out, the profile limits in case 2 go way beyond the size limits of case 1.

The question should have been posed with case 2 having a profile tolerance of .003. Make a sketch showing the profile boundaries (recall that it's bilateral but it wraps around the circle) and I think you'll see what I mean.

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

 

[greenimi]

pylfrm and J-P,

If the profile would have been within .003 (as J-P suggested), would be any differences within these cases?

Or to repeat the OP question in J-P’s adjusted scenario (profile within .003)

:” Can you indicate or imagine a scenario/case (how the pin should look like) that can be acceptable per one case, but not per the other?
In other words, how the form error, circularity, cylindricity, straightness, waiting, barreling will be affected by one case but not by the other. “

Thank you

 

[jassco]

Oops! I thought profile tolerance is 0.003 in my previous reply.

If the profile tolerance in case #2 is 0.003, then case 1 is same as case 2, isn't it? Per ASME Y14.5-2009, unless otherwise specified, the limits of size of an individual feature of size control the form of the feature as well as the size.

Best regards,

Alex

 

[Belanger]

Greenimi (and all) -- even then they wouldn't be the same, because of form allowances. Although the size limits would now match, the case using profile of a surface would require stricter form in terms of straightness.

Imagine a part where the actual local size (cross section) is made at a consistent .122. For case 1, that part could bend until its envelope pokes out to .128. A sketch will show that this puts all of the .006 error onto one side. But with case 2, I think the part of .122 couldn't bend at all.

Again, though, this is looking at straightness error of the feature of size. Errors of waisting or barreling would be the same in the two cases because waisting and barreling have the error equally distributed.

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

 

[gabimo]

J-P, pylfrm (and all),

Should I understand that in case #2 (your proposed case) Ø.125 basic and profile .003, the part must have a perfect form when made at LMC and also when made at MMC?

So, when a part has all actual local sizes (cross sections) made at a consistent .122, the part couldn’t bend at all and also must have a perfect circularity?
By the same token, when a part has all actual local sizes made at a consistent .128, the part also couldn’t bend at all and also must have a perfect circularity in all its cross sections?

Am I correct?

 

[pylfrm]

gabimot,

You are correct.


pylfrm