Edged tool positioning device for use in a machine tool

Disclosed is an edged tool positioning device which is fixed to the quill of a machine tool for permitting the edged tool to reach a desired X- and Y-coordinate position on a workpiece and for permitting the edged tool thus put at the desired X- and Y-coordinate position to advance a desired distance in the thickness of the workpiece in the Z-direction. Every time the device is brought in contact with at least one selected side and upper surface of the workpiece, a warning unit built in the device informs a worker of the contact by the device with the workpiece, thus permitting him to find a start position and measure a desired distance in each direction.

BACKGROUND OF THE INVENTION 
Field of the Invention 
The present invention generally relates to a drilling machine, a milling 
machine, a lathe or any other machine tool, and more particularly to a 
positioning device for putting an edged tool exactly at a desired position 
on a workpiece to be machined. 
Description of the Prior Art 
In an attempt to eliminate the necessity of complicated markings to find in 
a workpiece a desired position at which the workpiece is to be machined, 
the inventor proposed a device for putting the center of an edged tool of 
a machine tool exactly on a selected side of a workpiece, from which side 
the edged tool can move a measured distance to the desired position (See 
Japanese Utility Model Publication No. 50-43434). 
Referring to FIG. 1, such a proposed device comprises an elongated hollow 
cylindrical section 21 and a shortened hollow cylindrical section 22, both 
aligned on a common axis and resiliently connected to each other. In use 
the two-sectioned cylindrical device is fitted in the chuck 7 of a machine 
tool in place of an edged tool. The two-sectioned cylindrical device is so 
adjusted on its level that its shortened end section 22 is below the upper 
surface level of the workpiece 12 and that its elongated secton 21 remains 
above the upper surface level of the workpiece. Then, the cylindrical 
device while rotating is moved towards a selected side of the workpiece 
12. When the cylindrical device is brought in contact with the selected 
side of the workpiece 12, the shortened end section is somewhat displaced 
with respect to the elongated section as a counter action to the contact 
with the workpiece, and then the rotation of the cylindrical device 
automatically stops, indicating that the cylindrical device is put in 
contact with the selected side of the workpiece 12. Then, the cylindrical 
device is replaced by an edged tool, and the edged tool is moved a 
measured distance plus the radius of the edged tool to reach a desired 
coordinate position in an X-or Y direction. 
The proposed device, however, has a few disadvantages: after having found a 
start position, it is necessary to replace the device by an edged tool for 
performing required machining. The proposed device is useful only in two - 
dimensional positioning, or in finding a desired X-and Y-coodinate 
position, but it is useless in detecting a desired depth in a Z-direction 
(i.e along the axis of rotation of the edged tool). 
Because the two-sectional cylindrical device cannot put its shortened end 
section offset with respect to its elongated section as a counter action 
to the contact with the upper surface of the workpiece, the device cannot 
find a start point from which a desired depth is to be measured in the 
Z-direction. 
With the drawbacks of the prior art in mind the object of the present 
invention is to provide an edged tool positioning device eliminating the 
necessity of replacing the positioning device by the edged tool, still 
permiting a three-dimensional positioning in X-,Y-and Z directions with 
ease. 
SUMMARY OF THE INVENTION 
To attain this object an edged tool positioning device according to the 
present invention comprises: an edged tool holder which is adapted to be 
fixed to the body of a machine tool in the electrical insulating 
relationship with the machine tool body; and a series-combination of a 
warning device and an associated electric battery, said warning device 
being electrically connected both to said edged tool through said edged 
tool holder and to one terminal of said electric battery, and the other 
terminal of said electric battery being electrically connected to the body 
of said machine tool, thereby permitting the energization of said warning 
device when said edged tool is brought in contact with a workpiece lying 
on the worktable of said machine tool. 
In use, in finding an X-and Y- coodinate position, the tip of the edged 
tool is brought down to a level below the upper surface of a workpiece, 
and then the workpiece is moved towards the edged tool. When the workpiece 
is brought in contact with the edged tool, the warning device is put in a 
closed circuit with the electric battery, thereby causing an electric 
current to flow from the electric battery to the warning device through 
the body of the machine tool, the workpiece and the edged tool, informing 
a worker of the contact by the edged tool with a selected side of the 
workpiece. Then, the workpiece is moved a measured distance plus the 
radius of the edged tool, thus allowing the edged tool to reach an exact 
X-coodinate position. 
Likewise, a Y-coordinate position is found, and then the rotary center of 
the edged tool is brought to a desired X-and Y-coordinate position. Next, 
in determining a Z-coordinate position, the edged tool thus put at the 
desired X-and Y-coordinate position is lowered until it is brought in 
contact with the upper surface of the workpiece. The warning device again 
informs the worker of the contact by the edged tool with the upper surface 
of the workpice. Thus, a start point in the Z-direction is found. Now, the 
machine tool is set for allowing the edged tool to advance a desired depth 
in the Z-coodination.

DESCRIPTION OF A PREFERRED EMBODIMENT 
FIG. 2 shows a positioning device according to one embodiment of the 
present invention. In the drawing the quill of a drilling machine is 
designated at 1, and a cylindrical holder 3 made of a dielectric material 
such as ceramic is fitted in a downward divergent hole 2 at the end of the 
quill 1, and the holder 3 is fixed to the end of the quill 1 by means of 
bolts (not shown). A buzzer 4 and a dry battery 5 are fitted in the upper 
straight hole contiguous with the downward-divergent hole of the holder 3, 
and the minus terminal of the dry battery is connected to the quill via an 
associated resilient contact piece 6. A chuck is designated at 7, and is 
shown as a hollow metal cylinder whose cylindrical wall has a plurality of 
longitudinal slits 8, thereby permitting the same to reduce diametrically, 
resiliently yielding when an external force is applied therto. The chuck 7 
is pushed into the downwardly-divergent hole of the holder 3. The holder 3 
has an associated cap 9 threadly engaged with the open end of the holder 
3. Rotation of the cap 9 will cause the cylindrical chuck 7 to advance in 
the downwardly-divergent hole, reducing the cross-sectional area of the 
cylindrical body, and accordingly increasing the force with which a twist 
drill 10 is held until it is firmly gripped. A coiled spring 11 is put 
between the top of the chuck 7 and the casing of the buzzer 4, thereby 
providing an electrical connection there between. 
In operation, first, a workpiece 12 is put aside from the space just below 
the twist drill 10 on a worktable 13, and the tip of the twist drill 10 is 
lowered to a level below the upper surface of the workpiece 12. Then, the 
workpiece 12 is moved towards the twist drill 10. When the twist drill 10 
is brought in contact with a selected side of the workpiece, an electric 
current flows from the dry battery to the buzzer 4 via the twist drill 10 
and the workpiece 12, which together constitute a switch. Then, a sound is 
generated. 
The twist drill is raised above the workpiece 12, and is moved horizontally 
a measured distance from the selected side to a point at which a hole is 
to be made plus the radius of the twist drill, thus putting the tip of the 
twist drill exactly at the X-coordinate position as desired. 
Similarly the tip of the twist drill is brought exactly to the Y-coordinate 
position. Then, the twist drill 10 is lowered towards the workpiece 12 at 
the exact X and Y coordinates, and when the tip of the twist drill 10 is 
brought in contact with the upper surface of the workpiece 12, again the 
buzzer 4 sounds, and then the descent of the twist drill is made to stop. 
The level at which the descent of the twist drill stops is selected as the 
origin from which a desired hole depth is to be measured. 
When a positioning device is applied to a milling machine, a milling cutter 
is combined with the positioning device in the same way as the twist drill 
is combined with the device in the drilling machine above described. When 
a positioning device is applied to a lathe, its edged tool holder is used 
as a chuck 7, and therefore the tool holder need be provided with an 
appropriate insulator. 
If a plurality of small holes are made in the chuck body 3, the sound from 
the buzzer 4 is easy to hear. In place of the buzzer a lamp may be used, 
and if the buzzer and the lamp are used in combination, a worker can be 
informed more assuredly. As for necessary insulation between the quill and 
the twist drill it suffices that the chuck metal is coated with a 
dielectric material. 
As may be understood from the above, an edged tool is fixed to the body of 
a machine tool in an electrical insulating relationship with each other, 
and the edged tool is electrically connected to the body of the machine 
tool through a warning device and an associated electric battery, thus 
putting the warning device in closed circuit with the electric battery to 
sound when the edged tool is brought in contact with a workpiece lying on 
a worktable of the machine tool, informing a worker of the contact of the 
edged tool with the workpiece. Every time he is informed of the contact of 
the edged tool with the workpiece in each of the X-,Y-and Z-direction, he 
can put the edged tool in the exact X-and Y-coordinate positions, and can 
set a desired hole depth in the Z-direction. 
Immediately after completing the setting of the edged tool he can start 
machining without further delay. This assures machining at an increased 
efficiency.