Kitagawa HW-08 Instruction Manual Download

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3. Relationship between gripping force and rotation speed

As  the  rotation  speed  becomes  higher,  the  centrifugal  force  of  the  jaw  increases  and  the  gripping  force  lowers.  The
curves  displayed  in  Fig.  6  shows  relationships  between  the  rotation  speed  and  the  centrifugal  force  when  using  the
standard  soft  jaw.  The  centrifugal  force  differs  significantly  depending  on  the  size  and  shape  of  the  top  jaw  and  the
attaching  position,  therefore,  when  the  rotation  speed  is  high,  actual  measurement  using  a  Kitagawa  gripping  force
meter is required.

To avoid serious accidents caused by the chuck or work flying out:
・Determine the gripping force required for processing by the machine tool manufacturer or user, and check that

the required gripping force is provided before processing. The gripping force of the chuck must not exceed the
maximum static gripping force.

・Determine the rotation speed required for processing by the machine tool manufacturer or user based on the

gripping force required for the processing. The rotation speed at this point must not exceed the allowable
maximum rotation speed.

・When determining the cutting conditions, refer to pages 14-16.
・Pay attention since the gripping force is different depending on the state of the oil supply, grease in use, height of

the jaw, performance of the pump and the pressure reducing valve, piping state, etc.

3-2. Relationship between gripping force and rotation speed

1. Maximum static gripping force

The static gripping force is the gripping force when the chuck is at a stop.
The power chuck has a mechanism to convert input force (piston thrust force, draw pipe drawing force) from the cylinder
to gripping force. Therefore, the gripping force when the allowable maximum input force becomes the maximum static
gripping force.
However, the gripping force is different depending on the state of grease lubrication, grease in use, height of the jaw,
etc. The maximum static gripping force specified in the specification is the value under the following conditions:
・The Kitagawa standard soft jaw is used as the

jaw.

・The attaching bolts of the soft jaw are tightened

at the specified torque. (Refer to page 9)

・The numerical values are obtained with the

Kitagawa  gripping  force  meter  .  The  gripping
position  of  the  gripping  force  meter  is  at  a
position  1/2  of  the  height  of  the  soft  jaw  top
surface (height from the chuck surface to the top
surface of the jaw).

・CHUCK GREASE PRO is used. (Refer to page

21).

・A variable displacement pump with the discharge

volume  of  20  liters/min  or  more  is  used  as  the
hydraulic  source.  The  pressure  is  set  by  the
pressure control equipment of the pump itself, or
the  pressure  reduction  valve  equipped
separately.

2. Allowable maximum rotation speed

In the case of outside diameter gripping, when the chuck is rotated, the gripping force lowers due to the centrifugal force
of the top jaw. Therefore, the rotation speed when the dynamic gripping force (gripping force during rotation) becomes
approximately 1/3 of the maximum static gripping force is set as the allowable maximum rotation speed. The centrifugal
force is different depending on the mass of the top jaw and the barycentric position as well as the rotation speed. The
allowable maximum rotation speed specified in the specification is the value under the following conditions:
・The Kitagawa standard soft jaw is used.
・Grip the gripping force meter in the center of the jaw stroke, and at this point, the soft jaw is attached at the position

where the periphery side end of the soft jaw and the chuck periphery are almost lined up.

・The numerical values are obtained by the Kitagawa gripping force meter. The gripping position of the gripping force

meter is at a position 1/2 of the height of the soft jaw top surface (height from the chuck surface to the top surface of
the jaw).

・In the case of processing a considerably unbalanced work, lower the rotation speed. The work will fly out and this is

dangerous.

・Vibration is generated if there is unbalance due to the work and the jig, etc. Vibration decreases process precision

and shortens the working life of the chuck, even possibly breaking it. Correct the unbalance by using a balance
weight, etc., or lower the rotation speed for use.

・In the case of heavy cutting at high rotation speed, vibration is easily generated in the same manner as the unbalance

of the chuck, therefore, set the cutting conditions appropriate for the dynamic gripping force and machine rigidity.

Fig.6

3-3. Relationship between gripping part center height,

static griping force and input force /

Relationship between top jaw mass moment and gripping force loss

If the gripping part center height of the used top jaw (dimension H in Fig. 7) is higher than the gripping part center height of
the standard soft jaw, a large load is applied to the master jaw, T nut, jaw attaching bolts, etc. To prevent these parts from
being broken, it is necessary to use the machine by using a lower input force than the allowable maximum input force.
Additionally, if the top jaw is larger and heavier, the centrifugal force generated at the top jaw will increase. It is necessary
to examine the dynamic gripping force considering the centrifugal force and to use the machine at a rotation speed that
can withstand the cutting force.

Fig.7

A=B

G: Center of mass of the top jaw

m: Mass of the top jaw

r : Distance from the center of mass of the top jaw to the chuck center

H: Gripping center height

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