The "M" on datum feature reference B in the video is MMB (maximum material boundary). I think Don mislabels them at the beginning around 0.12 when he says "datum features are modified at MMC or LMC". What he should have said was "modified at MMB or LMB". MMC & LMC does not apply to datum features referenced in a feature control frame, they are material "conditions" (not boundaries) used on the tolerance of the feature of size.
This is typical of the respected Don Day! A Great tip for a Datum-shift & size diameter. T J (Tom) Vanderloop, Author & Technical Instructor-Consultant, AWS & SME-Leader
Hello Don, I have a small doubt about the part and the diagram here. At about 1:40 - "If the outside diameter is made closer to its lower limit of size" At about 1:55 - "And for that reason i have put an M...." For an Outer Circle, Lower Limit of Size would be in LMC.. Isn't it? An M will take the Outer Dia to its Maximum Size. When diameter reduces, your explanation further to this statement will make perfect sense.
That is correct. The M states that when the feature of size is at it's maximum (MMC), there can be no datum shift; it must be "perfect". So as you go down to LMC, you get more datum shift.
The "M" on datum feature reference B in the video is MMB (maximum material boundary). I think Don mislabels them at the beginning around 0.12 when he says "datum features are modified at MMC or LMC". What he should have said was "modified at MMB or LMB". MMC & LMC does not apply to datum features referenced in a feature control frame, they are material "conditions" (not boundaries) used on the tolerance of the feature of size.
For ASME Y14.5-1994, datum material modifiers are labeled mmc/lmc still. What you described is true for ASME Y14.5 2009,2018 where they changed that
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This is typical of the respected Don Day! A Great tip for a Datum-shift & size diameter.
T J (Tom) Vanderloop, Author & Technical Instructor-Consultant, AWS & SME-Leader
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Hello Don,
I have a small doubt about the part and the diagram here.
At about 1:40 - "If the outside diameter is made closer to its lower limit of size"
At about 1:55 - "And for that reason i have put an M...."
For an Outer Circle, Lower Limit of Size would be in LMC.. Isn't it?
An M will take the Outer Dia to its Maximum Size.
When diameter reduces, your explanation further to this statement will make perfect sense.
I think like that too. I'd use LMC
That is correct. The M states that when the feature of size is at it's maximum (MMC), there can be no datum shift; it must be "perfect". So as you go down to LMC, you get more datum shift.
Thank you. Finally understand!!!
In the special case where I have a part with just two holes, and the first hole is the datum for the second hole, does it then give a bonus tolerance?
Very good job
Good video!
Can somebody explain what to put into measuring report if the datum shift is placed on the drawing?
Thank you
How much can vary, calculation
This is not clear to understand it
Great