Page 568 - Dormer

GENERAL HINTS

TOLERANCE LIMITS

1. ON THE CUTTING dIAMETER OF STANdARd REAMERS
The diameter (d ) is measured across the circular land immediately behind the bevel or taper lead. The tolerance is
1
in accordance with dIN 1420 and is intended to produce H7 holes.

REAMER TOLERANCE REAMER TOLERANCE
diameter (mm) Tolerance Limit (mm) diameter (mm) Tolerance Limit (mm)

Over Up to and High Low Over Up to and High Low
including + + including + +
3 0.008 0.004 18 30 0.017 0.009
3 6 0.010 0.005 30 50 0.021 0.012
6 10 0.012 0.006 50 80 0.025 0.014
10 18 0.015 0.008

2. ON A H7 HOLE
The most common tolerance on a finished hole is H7 (see table below). For any other tolerance the figure and table
beneath point 3 can be used to calculate the reamers tolerance location and width.

HOLE TOLERANCE HOLE TOLERANCE
diameter (mm) Tolerance Limit (mm) diameter (mm) Tolerance Limit (mm)
Up to and High Low Up to and High Low
Over Over
including + + including + +
3 0.010 0 18 30 0.021 0
3 6 0.012 0 30 50 0.025 0
6 10 0.015 0 50 80 0.030 0
10 18 0.018 0

3. When it is necessary to define the dimensions of a special reamer intended to cut to a specific tolerance, e.g. D8,
this well proven guide can be used.

A =
Hole Tolerance
Reamer Tolerance
B =

IT = Tolerance Width
Dmax =
Max diameter of Hole
Min diameter of Hole
Dmin =
d =
Nominal diameter
1
Max diameter of Reamer
d max =
1
Min diameter of Reamer
d min =
1
diameter Tolerance Width (mm)
over over over over over over over over
Tolerance width 1 3 6 10 18 30 50 80
(microns) incl. incl. incl. incl. incl. incl. incl. incl.
3 6 10 18 30 50 80 120
IT5 4 5 6 8 9 11 13 15
IT6 6 8 9 11 13 16 19 22
IT7 10 12 15 18 21 25 30 35
IT8 14 18 22 27 33 39 46 54
IT9 25 30 36 43 52 62 74 87
IT10 40 48 58 70 84 100 120 140
IT11 60 75 90 110 130 160 190 220
IT12 100 120 150 180 210 250 300 350
e.g. 10mm hole with tolerance D8, Max dia = 10.062, Min dia = 10.040, Hole tol (IT8) = 0.022
Maximum limit: 0.15 x hole tolerance (IT8) = 0.0033, rounded up = 0.004
Minimum limit: 0.35 x hole tolerance (IT8) = 0.0077, rounded up = 0.008

Maximum limit for reamer = 10.062 - 0.004 = 10.058
Minimum limit for reamer = 10.058 - 0.008 = 10.050

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