Engineering Drawing Convention for Units of Measure

K

KWB64

#1
What is the correct drawing convention for showing units of measure on an engineering drawing? If you can site the standard where I can find this I would appreciate it. Thank-you:confused:
 
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Marc

Hunkered Down for the Duration with a Mask on...
Staff member
Admin
#2
A quick 'bump'. If any of you folks can help with this, my Thanks in advance!
 

Stijloor

Staff member
Super Moderator
#3
What is the correct drawing convention for showing units of measure on an engineering drawing? If you can site the standard where I can find this I would appreciate it. Thank-you:confused:
ASME Y14.5M-1994, clause 1.5.3 "Identification of Linear Units" on Page 5 states:

On drawings where all dimensions are either in millimeters or inches, individual identification of linear units is not required. However, the drawing shall contain a note stating UNLESS OTHERWISE SPECIFIED, ALL DIMENSIONS ARE IN MILLIMETERS (or IN INCHES, as applicable).
Hope this helps.

Stijloor.
 

Wes Bucey

Quite Involved in Discussions
#6
I have the 2009 version. Does not make a difference in what the OP was asking.

Both the 1994 and the 2009 version in Clause 1.5.3 state the same.

Stijloor.
I also have the 1994 version (with the "reaffirmed 1999" label) Sometimes our readers are not aware the ASME documents have the year of issuance as part of the doc number.

FWIW: to give credence that it is the definitive source for answer to the OP:

ASME describes the document in question thus:
A Global Highway for Mechanical Engineering
Communications: ASME Y14.5, Dimensioning
and Tolerancing
by Lowell W. Foster
[excerpted from page 8 & 9 of ASME Codes and Standards]
ASME Y14.5M-1994, Dimensioning and Tolerancing, which specifies engineering drawing requirements, originated in the 1950s. Over the years it has incorporated technical innovations such as the new electronic compatible systems. Its original goal was to delineate and define mechanical part hardware and to create a common technical drawing language for standardized drawing practices. It was also recognized that representing a perfect part on the drawing must include a permitted “tolerance” as a deviation from the perfect part (because perfection cannot be achieved in real production). This explains the dimensions and tolerances emphasis of Y14.5M. This standard is designated as an “Internationally Recognized Standard,” the standard of choice throughout much of the world.

ASME Y14.5M predominantly illustrates the Geometric Dimensioning and Tolerancing (GDT) language to capture the “function and relationships” of part features. This shows that the design requirements and dynamics of part features (e.g., holes, pins, slots, surfaces), as they relate in part function, fit, or assembly with mating parts, can be captured and specified with “geometric characteristics,” “datum references,” and the other tools of the system. For example, in a mating part situation where four pins on one part are to assemble with four mating part holes, would it not stand to reason that if a hole (any one of them and each individually) was produced away from its worst case low limit size as an individual feature (i.e., be larger within its size tolerance), that any permitted error (tolerance) of location of that hole could be increased an equal amount? In other words, size of features can have an effect on, compensate for, and assist in meeting the location tolerance. This is known as the “maximum material condition” principle and increases possible location tolerances, brings down costs of production, and makes using functional gaging principles possible, which ensures assembly and other advantages. The product designer can select this option or decide on a more stringent method (called “regardless of feature size”) when this dynamic is prohibited. Other controls delineate part form, orientation, profile, and location of features relative to design requirements. This is all done through the system’s symbolic language and the rules and guidelines provided in the standard. This useful, powerful, and widely recognized GDT language is now established as the best method for communicating design requirements. Through use of the GDT system, production, quality, inspection, tooling, programming, and all other supporting operations can meet the requirements using a greater range of methods.
 

Jim Wynne

Staff member
Admin
#7
What is the correct drawing convention for showing units of measure on an engineering drawing? If you can site the standard where I can find this I would appreciate it. Thank-you:confused:
ASME Y14.5M-1994, clause 1.5.3 "Identification of Linear Units" on Page 5 states:
FWIW: to give credence that it is the definitive source for answer to the OP:

ASME describes the document in question thus:
First, although the text Stijloor quotes is as good as any, there is no universally accepted method of declaring the units of measure used in drawing dimensioning. Some drawings will say nothing (especially those originating outside the US, where metric dimensioning is often assumed) some will just say "Metric" or "English" somewhere in the title block, and others will have a note similar to the one from Y14.5M.

Y14.5M is not "definitive" in any sense until two or more parties agree that it is.
 

Stijloor

Staff member
Super Moderator
#8
<snip>Y14.5M is not "definitive" in any sense until two or more parties agree that it is.
When an organization includes a reference to the Y.14.5 Standard in their drawing (specification), it becomes a requirement. And anyone using this drawing must use that standard for its interpretation.

Outside of the USA, drawings refer to the appropriate ISO 1101 standard and its associated documents or national equivalents.

Stijloor.
 

Jim Wynne

Staff member
Admin
#9
When an organization includes a reference to the Y.14.5 Standard in their drawing (specification), it becomes a requirement. And anyone using this drawing must use that standard for its interpretation.
Which is just what I said; it doesn't become "definitive" until two or more parties agree to it.

Outside of the USA, drawings refer to the appropriate ISO 1101 standard and its associated documents or national equivalents.
Outside the US sometimes the ISO standard is referred to, and sometimes it's not, just as Y14.5M is not universally referred to in the US, even when GD&T is used. Not only that, there are cases all over the world where one of the standards is called out on a drawing and the drawing dimensioning contradicts the standard.
 
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