Balancing limits
In accordance with DIN ISO 1940 the balance grade is denoted with G as well as
the units gmm/kg or µm respectively and is relative to the number of revolutions.
At a speed of 15,000 rev./min and a weight of 1 kg, G 6.3 corresponds with a
permissible center deviation between rotational axis and center of gravity axis of
the spindle of 4 µm. At twice the speed of 30,000 rev./min it would be 2 µm. If the
tool holder was only half the weight, i.e. 0.5 kg, the permissible counter balancing
tolerance is also halved. Aim of counter balancing is to fi nd a compromise between
the technically feasible and the economically effi cient. Because the radial inter-
change accuracy for a brand-new HSK holder can be 2 to 3 µm and for an ISO taper
shank holder can be 5 to 10 µm, it means an initial quality limit of G 2.5 or G 6.3
respectively at 10,000 rev./min.
Fine-balanced with
balancing bores in the fl ange
Pre-balanced with
balancing bores at the collar
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The following diagram shows the quality grades to DIN ISO 1940-1, i.e. the
permissible rest imbalance in relation to the balance body mass for different
counter balance qualities G relative to the maximum operating speed.
Pre-balanced with
balancing fl at at the tool body
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KEMMLER 13. 36