What are Material condition modifiers?
- GD&T on holes (and shafts) provides a powerful tool for increasing inspection yield without trial-and-error fitting or binning.
- Used when the size of the feature interacts with its location.
- If ⓜ the symbol appears after the tolerance, then the specified tolerance holds only at maximum material condition.
- As the feature departs from MMC, the amount of departure can be added to the position tolerance.
- MMC is commonly used for clearance-type applications.
- This feature control frame specifies the positional tolerance zone as a circle of diameter .010 at MMC, centred according to the basic dimensions given.
- The tolerance zone's size depends on the size of the hole.
- MMC of hole = .250
- LMC of hole = .255
- Similarly, if Ⓛ symbol is used, the stated tolerance holds at least material condition (LMC). As the part departs from LMC, the amount of departure is added to the position tolerance.
- LMC is commonly used for loose fits.
- If no modifier is specified, (or ⓢ symbol in past practice) then the stated tolerance holds regardless of the material condition of the feature. This is called RFS – regardless of size.
- RFS is commonly used for pressed fits.
The logic behind bonus tolerances
- Taking an example for MMC