Specifications

Design Ver. 0002 DS - 7
DS.2.1.1 POWER REQUIRED BY THE LOAD
The power demanded from a spindle motor in a turning or machining center is determined by
the cutting power.
A good cutting process requires the spindle motor to be working at constant power and with a
power range between 1:3 and 1:5.
The powers used for cutting in a lathe, mill, machining center with drilling are calculated as
shown below.
For a more accurate calculation of the power required, one must bear in mind different factors
such as cutting oil, material, shape of the tools, hardness of the material machined, etc.
For lathe work, a cutting blade forces against the part to be machined, while this turns as
shown in the Illustration. The power required, P
C
, is calculated as follows:
here:
K
S
is the relative cutting resistance in N/mm
2
.
d is the depth of the cut in mm.
L is the length of the blade, or feedrate per full turn in mm.
D is the diameter of the part machined in mm.
N
S
is the turning speed of the spindle in r.p.m.
ηη
ηη
η
C
is the mechanical efficiency (varies from 0.7 to 0.85).
S
C
is the cutting efficiency, that is, cut volume per kilowatt each minute in cm
3
/kW/min.
In the case of a milling machine, the cutter is mounted on the spindle itself and turns with this
to cut the material as shown in the Illustration. The power required in this case P
F
is
calculated as follows :
where:
K
S
is the relative cutting resistance in N/mm
2
.
d is the depth of the cut in mm.
W is the width of the cut in mm.
f is the feedrate in mm/min.
ηη
ηη
η
F
is the mechanical efficiency (varies from 0.7 to 0.8).
SF is the cutting efficiency that is, cut volume per kilowatt each minute in cm
3
/kW/min.
P
KdLV
dLV
S
C
S
CCC
=
60 1000** *
ηη
= (kW)
V
DN
S
=
π *
1000
(m / min)
P
KdWf
dWf
S
F
S
FFF
==
60 1000 1000
22
** ** ηη
(kW)