Basic Dimensions Required for True Position?
Basic Dimensions Required for True Position?
(OP)
An engineer I'm working with has dimensioned a part in a similar fashion to the example provided, where a Datum face is included in a True Position control frame but the basic dimensions giving the position of the hole are referencing another face which has its location relative to the Datum given with a non-basic dimension. The example makes this much clearer, please ignore the fact that the hole doesn't have both X and Y positions defined since it's immaterial to my question.
http ://files.e ngineering .com/getfi le.aspx?fo lder=d2fc9 a29-84f4-4 86d-b1e9-0 c4136b4742 4&file =Example_D rawing.JPG
Is this actually a correct way to dimension a part? Shouldn't the second face be another Datum and be referenced in the control frame instead? If the engineer is concerned with the position of the hole relative to the original datum, shouldn't they give the nominal position for the hole in basic dimensions? And if both matter, wouldn't a composite True Position tolerance be necessary?
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Is this actually a correct way to dimension a part? Shouldn't the second face be another Datum and be referenced in the control frame instead? If the engineer is concerned with the position of the hole relative to the original datum, shouldn't they give the nominal position for the hole in basic dimensions? And if both matter, wouldn't a composite True Position tolerance be necessary?





RE: Basic Dimensions Required for True Position?
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Basic Dimensions Required for True Position?
RE: Basic Dimensions Required for True Position?
A very similar question was asked recently and got quite a few responses as I recall, you may be able to find it.
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic Dimensions Required for True Position?
RE: Basic Dimensions Required for True Position?
What is Engineering anyway: FAQ1088-1484: In layman terms, what is "engineering"?
RE: Basic Dimensions Required for True Position?
"Good to know you got shoes to wear when you find the floor." - Robert Hunter
RE: Basic Dimensions Required for True Position?
RE: Basic Dimensions Required for True Position?
KENAT: Thank you for the alphabet soup! I hate having to have something like that to "point at" but sometimes it's necessary...
ewh: I think it would make his brain hurt, since it sure does mine.
RE: Basic Dimensions Required for True Position?
RE: Basic Dimensions Required for True Position?
It continues: "Basic dimensions establish a true position from specified datums..."
There's your ticket
John-Paul Belanger
Certified Sr. GD&T Professional
http://www.gdtseminars.com
RE: Basic Dimensions Required for True Position?
I remember seeing this was allowed the firs time I went through training. Technically, it is not "double-dimensioned", as there is no conflict for measuring and reporting.
RE: Basic Dimensions Required for True Position?
RE: Basic Dimensions Required for True Position?
RE: Basic Dimensions Required for True Position?
Peter Stockhausen
Senior Design Analyst (Checker)
Infotech Aerospace Services
www.infotechpr.net
RE: Basic Dimensions Required for True Position?
I have not got ASME Y14.5M-1982 in front of me. The datum box is from 1982. Is there any significance to this? This is a general question for everyone.
RE: Basic Dimensions Required for True Position?
Sorry if this is a dumb question. I understand the picture wasn't created to spec.
RE: Basic Dimensions Required for True Position?
RE: Basic Dimensions Required for True Position?