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Reaming tools
Manufacturing tolerances to DIN 1420
General remarks for the determi- more advantageous. hole tolerance (0.35 IT) below the
nation of manufacturing tolerances However, in the interest of econo- permissible maximum diameter
for reamers mic production and storage, it is d1max (ex. 1).
The manufacturing tolerances to recommended that non-standard Simplified determination of
DIN 1420 are allocated to certain manufacturing tolerances are perm. max. and min. reamer
tolerance zones of the holes to used only in exceptional cases. dimensions
be reamed. Generally they ensure For determing the manufacturing In order to facilitate calculations,
the positioning of reamed holes tolerances the following well-pro- the table on page 48 indicates
within the relevant tolerance zone ven basic rules were stipulated: the upper and lower tolerance
as well as the most economical limits on the nominal diameter d1
use of the reamer. Determination of perm. max. and for the most common “H” tole-
It must, however, be taken into min. sizes of reamers rance zones. With the aid of these
account that the size of the reamed The largest permitted reamer dia- tolerance limits the permissible
hole depends, in addition to the meter ranges at about 15% of the maximum and minimum reamer
manufacturing tolerance of the approximate hole tolerance (0.15 dimensions can be calculated (ex.
reamer, on various other factors, IT) below the permissible maxi- 2).
such as angles of cutting edges; mum diameter of the hole (see
bevel lead of reamer; clamping fig.), whereby the value 0.15 IT will
of the workpiece; the tool hol- be rounded of to the next higher
der; condition of the machine; the integer or half µm-value, so that
coolant and on the material of the even µm values are derived for
workpiece. Therefore, from time rde1ammaxe. rTdhieampeetremr idss1imbilne smallest
to time other manufacturing tole- ranges at
rances than IT7 (H7) might prove about 35% of the approximate
Example 1
nominal diameter d1 = 20.000 mm minimum reamer diameter:
maximum diameter of the hole = 20.021 mm d1 min = d1 max – 0,35 IT 7
= 20.017 – 0.008
hole tolerance (IT 7) = 0.021 mm = 20.009 mm
15% of the hole tolerance (0.15 IT 7) = 0.0031 mm
0.004 mm Example 2
maximum reamer diameter: nominal diameter d1 = 20.000 mm
d1 max = 20.021 – 0.004 = 20.017 mm upper tol limit (s. table p. 48) + 17 µm = 0.017 mm
manufacturing tolerance of reamer: lower tol. limit (s. table p. 48) + 9 µm = 0.009 mm
35% of the hole tolerance (0.35 IT 7) = 0.0073 mm i. e.: d1 max = 20.000 + 0.017 = 20.017 mm
0.008 mm d1 min = 20.000 + 0.009 = 20.009 mm
Simplified calculation of the permissible maximum and minimum dimensions for reamers
Example: Hole tolerance zone 20 H7/nom. dimension d1 of reamer 20 mm
Tolerance zone of Tolerance zone of
hole reamer
max. dimension d1 max max. dimension
min. dimension d1 min min. dimension
Tolerance zone Tolerance zone
(i.e. 20H7)
+0.017 (permissible max. dimension)
20.017 Manufacturing tole-
20.009 rances for reamers
+0.009 (permissible min. dimension)
20.000 Zero-line
20.021 0.021 (basic tolerance IT7)
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