datum reference style old new on y14.5m standard drawing
 

datum reference style old & new on y14.5m standard drawing?
we are using asme y14.5m-1994 (r2004) on our detail drawings and i have a question. i am being told that the standard says one can use the old style datum reference (i.e.: -a-) under the new standard. is this true? i have not been able to find this statement in the standard yet.
gary ashby
designer
ug/nx v8 thru nx5
solidworks 2007
autocad 2002 & 2008
eng-tips forums is member supported.
4mranch1,
i cannot find it either. the change history notes that they changed the datum feature symbols over to the iso version as part of the 1995 revision. perhaps they missed one.
i looked at the start of chapter_4, as well as at section_3.2.2.
jhg
a5 seems pretty definite about "the universal (iso) datum feature symbol is adopted and replaces the previous one."
and even in the body it doesn't use the weak 'should' which allows people so minded to ignore the intent of the standard.
while i can't be 100% sure i'm tempted to say you're being told wrong.
kenat, probably the least qualified checker you'll ever meet...
i cannot find anything in the standard stating that the old datum symbol can be used and i have studied the standard quite extensively.
i would suggest using the new one if you state in your drawing "complies to asme y14.5m-94".
dave d.
thanks all for your input on this. i pointed out to this individual that our drawing titleblock stated "interpret drawing per asme y14.5m-1994 (r2004)", but he insisted that it was an acceptable practice. i was thrown by the statement and came to this forum for some back-up.
if anyone can find anything that would make this practice allowable please let me know so i can confront this mis-statement with confidence.
gary ashby
designer
ug/nx v8 thru nx5
solidworks 2007
autocad 2002 & 2008
turn it around on the offender, ask him to show you where in the standard it says it is permissable. you could back this up by showing all the places it says to use the iso symbol.
of course politically this may not be a good idea but if i was good at politics i'd be a manager by now!
kenat, probably the least qualified checker you'll ever meet...
"acceptable practice" and following standards are not the same. that means he is saying "i don't know the standard and don't care, this is how i do it".
stick to the new standard.
i don't know if anywhere it says the old standard is acceptable in the new standard.
tell him that the next time he gets the wrong part replaced in his car that it is "acceptable practice".
chris
solidworks/pdmworks 08 3.1
autocad 06/08
appendix a touches on, and appendix d (neither being part of the asme y14.5m-1994 standard) illustrates the former practice. these are the only references i noticed between the asme front and back covers.
due to cad system nueances when it came to switching standards, i have occasionally left them on the print.
weavedreamer,
do i understand that you have changed an existing drawing that was prepared to an earlier version, and updated to the 1994 version?. if so, what is the value added and what statement is made on the drawing with regards to the 'prepared in acccordance with...' note?
if nothing else the forum posters here sure cover the bases. thanks all for your help. i will address this person with diplomatic finess and see if i can turn this injustice around.
gary ashby
designer
ug/nx v8 thru nx5
solidworks 2007
autocad 2002 & 2008
ringman,
the old, 'make it the same as, except' routine. the note claims in accordance with asme y14.5m-1994, while the biggest value added is the composite callout clarity provided by the 1994 standard over the 1982 compendium.
when addressing the feature of size, i've used a dimension of the feature showing the -datum- rather than the dimension for repeats. technically, the datum callouts should have been changed.
a paper written on the subject of going from 1982->1994 was written by the president of eti:
items to consider when converting a drawing from the
ansi y14.4m – 1982 to the asme y14.5 m – 1994 standards
by alex krulikowski
5/1/1998
many companies have switched from using the 1982 version of y14.5 to the 1994 version of y14.5. making new drawings to the standards is challenging, but there are many training courses that help the designer to use the new standard. when it comes to converting an existing drawing made to the 1982 asme standard to the 1994 asme standard there are not many (or any) materials to guide the designer.
hundreds of thousands of drawings are in existence, many are in accordance with the 1982 asme standard and may need to be updated. some designers think that simply changing the note that specifies which standard applies is enough, but that idea is a huge oversimplification. many subtleties must be addressed or the updated drawing will describe a different part.
if you want a drawing made to the 1994 version of the standard to say exactly what the drawing said when it was presented in the 1982 standard, the following items should be considered:
1. update the note that invokes the dimensioning and tolerancing standards.
2. determine if any detail dimensions need to be repeated on assembly drawings.
3. review the part configuration to determine if any shapes that were features of size now become features and need additional controls.
4. revise the datum specifications to the new datum symbol.
5. evaluate the radius specifications to determine if they should be controlled radii.
6. evaluate position tolerances for correct modifier specifications.
7. update projected tolerance zone specifications.
8. evaluate multiple single-segment and composite feature control frames to ensure their interpretation is as intended.
9. evaluate the use of a "boundary" note on elongated holes to remove axis interpretation.
10. evaluate composite profile tolerances to determine if orientation-only interpretation is desired.
11. in profile applications, replace the note for "between points" with the symbol for between.
12. evaluate concentricity callouts for desired part requirements; they may need to be replaced with position callouts.
13. determine if separate gaging should be specified for some position and/or profile specifications.
14. determine if the free state modifier should be specified.
15. evaluate orientation controls for application of the tangent plane modifier.

note: the explanations below assume the reader has a basic understanding of the y14.5 1982 & 1994 standards.
explanation of items
1. update the note that invokes the dimensioning and tolerancing standards.
updating the standards referenced note is probably the most obvious change that needs to be done. the note that specifies which standards applies to the drawing needs to be updated to read, "per asme y14.5m – 1994."
2. determine if any detail dimensions need to be repeated on assembly drawings.
the y14.5 1982 version did not specify if a detail dimension applies on an assembly of the detail. some companies used the interpretation of the standard to be that the dimensions on the detail drawing also applied at the up assemblies of the drawing. the y14.5 – 1994 version states that a dimension only applies at the drawing level in which it is specified. if a dimension is to apply at the assembly level, the dimension must be stated on the assembly drawing (not as a reference dimension).

3. review the part configuration to determine if any shapes that were features of size now become features and need addition controls.

in the 1994 version of y14.5, the definition of a feature of size was revised to require that the sides of a parallel plane feature of size are opposed. all dimensions that were feature of size dimensions on parallel plane features of size in the 1982 standard may not be features of size when the 1994 definition is applied. the major impact is the automatic application of rule #1. additional controls may need to be applied to control the form of part features that were automatically covered by rule #1 in the 1982 standard.
4. revise the datum specifications to the new datum symbol.
the datum symbol has been revised in the 1994 standard. it now matches the datum symbol from the iso standards. particular attention needs to be paid to the location of the triangle when converting datum identification symbols.

5. evaluate the radius specifications to determine if they should be controlled radii.
the definition of a radius has been revised in the 1994 version of y14.5, and a new controlled radius symbol has been added. a radius specified on a drawing to the 1982 standard is actually a controlled radius on a drawing to the 1994 standard.
6. evaluate position tolerances for correct modifier specifications.
rule #2 has been revised in the 1994 version of y14.5. it now states that all geometric controls apply rfs, unless otherwise specified. in the 1982 version of y14.5, rfs was specified in certain cases. each drawing should be reviewed and updated accordingly. rfs symbols may need to be removed from the position callouts.

7. update projected tolerance zone specifications.
in the 1994 version of y14.5, the way a projected tolerance zone is specified has been revised. each position symbol on the drawing should be reviewed to determine if it needs to be updated.
8. evaluate multiple single-segment and composite feature control frames to ensure their interpretation is as intended.
in the 1982 version of y14.5, the rules for composite positional tolerances in industry were interpreted two different ways. the 1994 version of y14.5 eliminates one of the ways composite tolerancing was interpreted in industry. each position symbol on the drawing should be reviewed to determine if it needs to be updated.

9. evaluate the use of a "boundary" note on elongated holes to remove axis interpretation.
in the 1982 version of y14.5, the tolerance zone for elongated holes was interpreted two different ways – axis and boundary. the use of the word "boundary" limits the interpretation of the tolerance zone of elongated holes to the boundary interpretation. each application of an elongated hole should be reviewed to determine if the tolerancing is correct.
10. evaluate composite profile tolerances to determine if orientation-only interpretation is desired.
in the 1994 version of y14.5, a definition for composite profile tolerances was added. it explains the use of the lower segment of a composite profile callout to be orientation-only. each composite profile used on a drawing based on the 1982 standards should be reviewed to determine if it is acceptable to use the orientation only-interpretation.

11. in profile applications, replace the note for "between points" with the symbol for between.
in the 1994 version of y14.5, a new symbol was added to specify that a tolerance applies between two points. it replaces the word "between," which is commonly used on drawings made to the 1982 version of y14.5. when converting the drawing, the new symbol should be used to indicate between.
12. evaluate concentricity callouts for desired part requirements; they may need to be replaced with position callouts.
in the 1994 version of y14.5, the definition of concentricity has been revised. concentricity now applies to the mid-point of a two-point measurement of the toleranced feature. if a concentricity symbol was used on a drawing made to the 1982 standards, it should be reviewed to determine if position rfs should be used on the drawing made to the 1994 standards.
13. determine if a separate requirement (gaging) should be specified for some position and/or profile specifications.
the rule for when a simultaneous requirement (gaging) applies has been expanded. it now applies to single features, and both position and profile callouts. when a drawing is converted, position and profile callouts should be evaluated to determine if any separate requirements automatically change to simultaneous requirements.
14. determine if a free state modifier should be specified.
in the 1994 version of y14.5, a new symbol has been added for free state. this symbol would only be used if a drawing contains a restraint note. the use of this symbol would most likely be replacing notes from an earlier drawing.
15. evaluate orientation controls for application of the tangent plane modifier.
in the 1994 version of y14.5, a new symbol has been added for tangent plane. this symbol actually allows more tolerance when it is used. if the flatness of a feature that is toleranced with angularity, perpendicularity, or parallelism does not have to be held to the same tolerance of the orientation control, the tangent plane modifier may be a worthwhile consideration. (the use of a tangent plane modifier would not be typical in a drawing conversion, but its use may reduce cost.)
conclusion
this list of items to consider when converting a drawing using the 1982 standard to the 1994 standard is based on my experiences when converting drawings. the list may not totally encompass all the items to be addressed. if you know of addition items that should be added to this list, let me know and i will update the list.