SME
Manufacturing Processes
Tolerances
Use this for “A 25 mm H7/g6 fit: the hole is 25.000–25.021 mm and the shaft 24.980–24.993 mm. Find the clearances and name the fit.”
Diagram
Cₘₐₓ = largest hole − smallest shaft = 25.021 mm − 24.98 mm = 0.041 mm.
Cₘᵢₙ = smallest hole − largest shaft = 25 mm − 24.993 mm = 0.007 mm.
Both are positive: a clearance fit, the shaft always slides in.
Deviations are enlarged; the zero line is the basic size.
Fit tolerance Tf = 0.034 mm
This is an example. Type your own values to start a new problem.
Cₘₐₓ (mm)
=
Dₘₐₓ (mm)
−
dₘᵢₙ (mm)
Cₘᵢₙ (mm)
=
Dₘᵢₙ (mm)
−
dₘₐₓ (mm)
Tf
Fit tolerance
calculated
fit
Kind of fit
worked out (not typed)
Formulas
Cₘₐₓ = Dₘₐₓ − dₘᵢₙ
0.041 = 25.021 − 24.98
Cₘᵢₙ = Dₘᵢₙ − dₘₐₓ
0.007 = 25 − 24.993
Tf = Cₘₐₓ − Cₘᵢₙ
0.034 = 0.041 − 0.007
fit: clearance if Cₘᵢₙ ≥ 0, interference if Cₘₐₓ ≤ 0, else transition
0.007 ≥ 0, so clearance
Assumptions
•
Hole basis: the smallest hole is the basic size, the zero line of the picture.
•
Each part may be made anywhere between its limits.
•
A negative clearance is an interference: the shaft is bigger than the hole.
Step-by-step
WE KNOW
Dₘₐₓ = 25.021 mm, Dₘᵢₙ = 25 mm, dₘₐₓ = 24.993 mm, dₘᵢₙ = 24.98 mm
FIND
largest clearance (Cₘₐₓ), smallest clearance (Cₘᵢₙ), fit tolerance (Tf), kind of fit (fit)
Step 1 · Find largest clearance (Cₘₐₓ)
Use Cₘₐₓ = Dₘₐₓ − dₘᵢₙ
The loosest pair is the largest hole with the smallest shaft.
Cₘₐₓ = 25.021 − 24.98
Cₘₐₓ = 0.041 mm
Step 2 · Find smallest clearance (Cₘᵢₙ)
Use Cₘᵢₙ = Dₘᵢₙ − dₘₐₓ
The tightest pair is the smallest hole with the largest shaft.
Cₘᵢₙ = 25 − 24.993
Cₘᵢₙ = 0.007 mm
Step 3 · Find fit tolerance (Tf)
Use Tf = Cₘₐₓ − Cₘᵢₙ
The fit tolerance is how much the clearance can vary from one pair to the next.
Tf = 0.041 − 0.007
Tf = 0.034 mm
Step 4 · Find kind of fit (fit)
Use fit: clearance if Cₘᵢₙ ≥ 0, interference if Cₘₐₓ ≤ 0, else transition
Even the tightest pair slides, so it is a clearance fit.
0.007 ≥ 0: clearance
fit = clearance if 0.007 ≥ 0, interference if 0.041 ≤ 0, else transition
fit = clearance
Check
Put the numbers back in. Both sides should match.
0.041 = 25.021 − 24.98 ✓
0.007 = 25 − 24.993 ✓
0.034 = 0.041 − 0.007 ✓
0.007 ≥ 0, so clearance ✓
Topic check
See what you know: 5 questions on this topic
New questions each time. Pass to mark it complete.
More problem types
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Use this for “A shaft is 25.000 ± 0.030 mm. The process runs at a mean of 25.006 mm with σ = 0.008 mm. Find Cₚ, Cₚₖ and the share outside.”
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Use this for “A 25.000–25.021 mm hole takes a 25.002–25.015 mm shaft. Which kind of fit is it?”