New Engineer learning GD&T with some questions
Hi fellow engineers,
I'm fresh out of school and still coming to terms with Y14.5 2009 standards. While I'm learning, I have some questions I hope some experienced engineers here can help me with:
DATUMS: I often see drawings with defined primary (A), secondary (B), and tertiary (C) datums, and then a hole that has a datum reference frame with a location tolerance applied at A B C. But a book I am studying from tells me that we can switch the datum order to set a part up at B C A. Is that allowed if the drawing already specified A to be primary, B to be secondary (relative to A), and C to be tertiary (relative to A and B)?
The other thing I'm seeing is often a drawing would define a datum D or E that is a feature based on A B C. Then another feature would be defined with a location tolerance with datums A D B. Is that allowed? Shouldn't B be before D?
STRAIGHTNESS:
When it's straightness of a size dimension like a diameter, what is the derived median line? How do you find the derived median line realistically?
PROFILE:
This book says we can use profile for everything, but if we can use a size dimension refined by orientation, form, or location, is that a better way of defining things than putting a profile tolerance and using some basic dimensions?
Any and all help would be greatly appreciated! Thank you guys so much!