Virtual Condition
For a shaft that fits into a hole, the shaft virtual condition must be smaller than the hole virtual condition.
For an external feature of size such as a shaft, the virtual condition is equal to the size at MMC plus the size of the position tolerance zone.
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| Shaft with MMC applied |
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| Shaft Virtual Condition |
For an internal feature of size such as a hole, the virtual condition is equal to the size at MMC minus the size of the position tolerance zone.
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| Hole with MMC applied |
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| Hole Virtual Condition |
Since the shaft virtual condition is smaller than the hole virtual condition, the two parts will always mate.
Virtual condition is extremely useful in design of functional gauges. A functional gauge made to virtual condition will ensure that a part will always mate with its counterpart.
In summary, the way to calculate virtual condition (VC) for a shaft and hole is:
SHAFT VC = MMC Diameter + Position Tolerance Zone Diameter
HOLE VC = MMC Diameter - Position Tolerance Zone Diameter
Resultant Condition
For a internal feature of size, the resultant condition is the variable value and outermost boundary.
For a external feature of size, the resultant condition is the variable value and innermost boundary.
The way to calculate resultant condition (RC) for a shaft and hole is:
SHAFT RC = AME - Total Tolerance
HOLE RC = AME + Total Tolerance
HOLE RC = AME + Total Tolerance
Whereas AME is Actual Mating Envelope &
Total Tolerance = Bonus Tolerance + Geometric Tolerance
Lets us consider a case study for Virtual & Resultant condition.
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| Internal feature of size |
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| Calculation Table Internal feature of size |
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| External feature of size |
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| Calculation Table External feature of size |
Summary
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| Comparison Table for Internal Feature of size |
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| Comparison Table for External Feature of size |
Note : virtual condition and resultant condition are applicable only for specification with material condition. Therefore in Regardless of feature size ( RFS ), the similar substitute are inner and outer boundary.
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ReplyDeleteabove example, virtual condition for hole is equal at .235 and for pin is .265. How the virtual condition of hole is smaller than pins? please explain to me.
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ReplyDeleteinner and outer boundary in figure "Comparison Table for Internal Feature of size" has to be replaced each other.
ReplyDeletewhat is bonus tolerance
ReplyDeleteBonus tolerance is an additional tolerance which we get by calculating the difference between the Maximum material condition [Pin] & Actual size of it when we have M modifier beside the tolerance value in Feature control frame.
DeleteIf you can understand this then you try out considering the L modifier and also for Hole features.
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ReplyDeleteAccording to ASME Y14.9-2009 page 32 example 2-12, the resultant condition RC for internal feature is a single value ( Not Variable as you mentioned) equals to its least material condition plus its applicable geometric tolerance.
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