SME
Engineering Graphics & CAD · Problem type
Bonus tolerance at MMC
Use this for “A hole sized Ø10 to Ø10.2 mm has position Ø0.1 at MMC and measures Ø10.15. How much position tolerance does it get?”
Diagram
A hole: MMC is its smallest size, 10 mm, where the zone is the stated t = 0.1 mm.
At d = 10.15 mm: b = |d − MMC| = 0.15 mm and T = t + b = 0.25 mm.
Every bit the size moves away from MMC is added to the position zone.
This is an example. Type your own values to start a new problem.
b (mm)
=
|
d (mm)
−
MMC (mm)
|
T (mm)
=
t (mm)
+
b (mm)
LMC
Size at LMC
example · mm
Formulas
b
=
d
−
MMC
0.15 = 10.15 − 10
T
=
t
+
b
0.25 = 0.1 + 0.15
Assumptions
•
The tolerance is stated at MMC (the circled M in the frame).
•
A hole’s MMC is its smallest size; a shaft’s MMC is its largest size.
•
The actual size is already within its size limits, MMC to LMC.
Step-by-step
WE KNOW
MMC = 10 mm, LMC = 10.2 mm, d = 10.15 mm, t = 0.1 mm
FIND
bonus tolerance (b), total tolerance (T)
Step 1 · Find bonus tolerance (b)
Use b = d − MMC
A hole: the bonus is how far the actual size has grown past its smallest size, MMC.
10.2 > 10: a hole, so MMC is its smallest size
b
=
10.15
−
10
b
=
0.15
mm
Step 2 · Find total tolerance (T)
Use T = t + b
The total tolerance is the stated tolerance plus the bonus.
T
=
0.1
+
0.15
T
=
0.25
mm
Check
Put the numbers back in. Both sides should match.
0.15 = 10.15 − 10 ✓
0.25 = 0.1 + 0.15 ✓
Topic check
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