GD&T : Calculating the geometric tolerance for a hole in a part
Mufaddal Rasheed 
How to calculate the geometric tolerance available for a hole manufactured at different sizes for given drawing
For the drawing of the block with two holes,
What would be the tolerances for different sizes of the hole dia. 15 highlighted in red box ?
Case 1 :
When hole is manufactured at size of 15.1
Hole will be largest possible size, this is Least material condition .
Bonus tolerance = manufactured value - Maximum Material Condition = LMC value – MMC value = 15.1-14.9 = 0.2
Existing geometric tolerance = 0.2 (in feature control frame)
Total tolerance applicable = 0.2 + 0.2 = 0.4
So the Hole when manufactured at LMC which is 15.1 can vary in its position within a tolerance zone of 0.4mm diameter.
Case 2 :
When hole is manufactured at size 14.85
Bonus tolerance = manufactured value - Maximum Material Condition = 14.85 – 14.9 = 0.05 mm
Existing geometric tolerance = 0.2 (in feature control frame)
Total tolerance applicable = 0.05 + 0.2 = 0.25 mm.
So the Hole when manufactured at 14.85 mm can vary in its position within a tolerance zone of 0.25 mm diameter.
Virtual condition of the hole :
Virtual condition of hole = MMC – geometric tolerance in feature control frame
MMC = 14.9 mm
Virtual condition = 14.9 – 0.2 =14.7 mm
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Categories: : GD & Tolerancing