I'm the one who said "keep it simple." However, when trying to explain an overall topic you have to cover all bases otherwise you get, but what about this, and what about that? Parts fit together on a MMC basis. LMC is only for controlling thin walls or whatever and has nothing to do with the...
Keep it simple. Dimensioning for interchangeability is the subject. End item drawings should maintain the boundary of interchangeability even when tolerances change. Nominal dimensioning makes the MMC/VC boundary a moving target and possibly destroys interchangeability, forcing a new part number...
Which came first, the chicken or the egg; the flea or the dog? On the one hand you have boundary conditions, but on the other hand boundary conditions are defined by their tolerances, or are they? Tolerances are variables that have to be tied to something. So right off the bat tolerances can't...
With castings you are normally only concerned with machined surfaces that mate and fit with other parts within an assembly. Some companies do not even dimension cast surfaces and default to the model STP with a general note specifying a loose profile tolerance per ASME Y14.5-2009, para. 8.3.1.1...
Fit calculations should be considered pre-product manufacturing data. Those calculations don't work by the way with purchased pins. End product verification is only concerned with MMC of the pin in relation to the datum reference frame of the assembly.
I had hoped that my PDF file would have explained everything. It says that upload was successful.https://files.engineering.com/getfile.aspx?folder=7a67fb80-e497-4b1d-890d-4d02d669872e&file=Dimensioning_for_Interchangeability.pdf
I tried the attachment button again. Hope this time it goes through.https://files.engineering.com/getfile.aspx?folder=c4a2626b-7896-464a-806e-9ade827eb859&file=GD&T-The_American_System.pdf
Would like to start a long overdue discussion of the significance of the ASME Y14.5, paragraph 2.7.1(a) statement: “The surface or surfaces of a feature shall not extend beyond a boundary (envelope) of perfect form at MMC. This boundary is the true geometric form represented by the drawing”...
