Page 7 - MILLING CATALOG p549-788

INTRODUCTION TOOLING SYSTEMS

Balancing Elements

Balancing Definitions Balancing Coolent Chucks

Introduction m

Balancing is the process of equalizing the mass r
distribution of a body so it rotates in its bearing
without unbalanced centrifugal forces. Example 1
U=2 g x mm can be treated as an unbalance mass
Balancing causes reduced vibration, lower of m=2 g in radial distance of r=1 mm or as a mass
spindle strain and improved machining qualities, of m=0.1 g in radial distance of r=20 mm, etc.
and allows for higher cutting parameters.
Example 2
The measuring equipment available today enables The residual unbalance is independent of the speed.
unbalance to be reduced to low limits. However, it would This value reflects the unbalance mass and its distance
be uneconomical to exaggerate the quality requirements. from the true center of mass. The residual unbalance
It has therefore become necessary to determine to what value is measured on balancing machines.
extent the unbalance should be reduced and where
the optimum economic and technical compromise
on balance quality requirements would be struck.

Definition

G - Balance quality (mm/s) U = m ∙ r = >m = U = 4 = 0.2g
e - Specific unbalance (gxmm/Kg) r 20
Ω - Speed (rad/s)
N - Speed (rpm) G value reflects the balancing quality of a
M - Mass of the body (kg) toolholder according to its rotational speed (N)
m - Mass of the unbalance (g)
r - Radius of the unbalance (mm)
U - Residual unbalance (gxmm)

e= U =>U=M∙e G =Ω∙e= π∙N ∙ U = U∙N∙π
M 30 M M ∙ 30

Ω= 2πN = πN e= G ∙ 30
60 30 π∙N

Operation Example 3
G value reflects the balancing quality of a toolholder
Residual unbalance equals the tool’s mass (M) according to its rotational speed (N).
times its eccentricity (e). Eccentricity measures the
extent to which the tool’s weight is off-center. G = π ∙ N ∙ U = π ∙ 15, 000 ∙ 8 ≈ 6.3 (mm/s)
30 M 30 2, 000
It is defined as the distance from the tool’s center of the
rotation to its true center of mass. e= U =e= 8 = 4 (g ∙ mm/kg)
If eccentricity is measured in microns and tool M 2
mass is measured in kilograms, this unit yields
residual unbalance in gram-millimeters. The G value will change to G=2.5 mm/s when using the
same toolholder at a rotational speed
Any two sets of mass and eccentricity that yield the N=6, 000 rpm and to G=1.0 mm/s at
same unbalance value will have the same effect on N=2, 500 rpm.
the tools, so long as the residual unbalance is in the
same plane perpendicular to the rotation axis. Balance quality grades for various
groups of representative rotors:
U=r∙m
• General machine tool parts - G6.3
The residual unbalance is independent of the speed. • General toolholders and machine drivers - G2.5
This value reflects the unbalance mass and its distance • Grinding machine drivers - G1.0
from the true center of mass. The residual unbalance • Spindles of precision grinders - G0.4
value is measured on balancing machines.

555