Drill, drilling unit, and drilling method

According to one implementation, a drill includes: a body without a back taper and a cutting edge part. The body has a flow path of a cutting oil. The flow path is branched to first and second flow paths inside the body. The cutting edge part has a first supply port that supplies the cutting oil toward a workpiece. The first supply port is an outlet of the first flow path. The body has a second supply port that supplies the cutting oil to a clearance between the body and a bush for positioning the body. The second supply port is an outlet of the second flow path. The second flow path has a pressure loss by which the cutting oil is not scattered from the second supply port in a radial direction of the body but exuded from the second supply port.

CROSS REFERENCES TO RELATED APPLICATIONS

This application is based upon and claims the benefit of priority from Japanese Patent Application No. 2018-231043, filed on Dec. 10, 2018; the entire contents of which are incorporated herein by reference.

FIELD

Implementations described herein relate generally to a drill, a drilling unit, and a drilling method.

BACKGROUND

Conventionally, a drilling method using a drilling jig, such as a drilling plate and/or a guide bush, is known as one of drilling methods. As a specific example, a drilling method for deep hole processing with high precision using a guide bush, which can supply cutting oil inside, has been proposed (for example, refer to Japanese Patent Application Publication JP2015-120216 A).

In drilling using a drill, supplying cutting oil leads to improvement in drilling precision and a tool life. Accordingly, a technique to form a flow path of cutting oil inside a drill to supply the cutting oil toward a workpiece from a cutting edge of the drill is known. As a specific example, a drill in which discharge ports of cutting oil have been formed in cutting edges in addition to lands has been proposed (for example, refer to Japanese Patent Application Publication JP2009-83092 A).

An object of the present invention is to allow drilling with higher precision in the case of drilling by inserting a drill into a guide bush.

SUMMARY OF THE INVENTION

In general, according to one implementation, a drill includes: a body without a back taper and a cutting edge part. The body has a flow path of a cutting oil inside. The flow path is branched to a first flow path and a second flow path inside the body. The cutting edge part is integrated with the body. The cutting edge part has a first supply port that supplies the cutting oil toward a workpiece. The first supply port is an outlet of the first flow path. The body has a second supply port that supplies the cutting oil to a clearance formed between the body and a bush for positioning the body. The bush is used by inserting the body inside the bush. The second supply port is an outlet of the second flow path. The outlet of the second flow path is formed on an outer peripheral surface of the body. The second flow path has a pressure loss by which the cutting oil is not scattered from the second supply port in a radial direction of the body but exuded from the second supply port.

Further, according to one implementation, a drilling unit includes the above-mentioned drill and the bush.

Further, according to one implementation, a drilling method for producing a drilled product includes: using at least the above-mentioned drill and the bush for drilling the workpiece; and supplying the cutting oil.

DETAILED DESCRIPTION

A drill, a drilling unit, and a drilling method according to implementations of the present invention will be described with reference to the accompanying drawings.

FIG. 1shows a structure of a drilling unit including a drill according to the first implementation of the present invention.FIG. 2shows a state where the drilling unit shown inFIG. 1is drilling a workpiece.

A drilling unit1drills a workpiece W using a handheld drill driving device, having at least a rotor for rotating a desired cutting tool. The drilling unit1has a drill2, a guide bush3, and a drilling plate4. The guide bush3is used for positioning the drill2, by being inserted into a through hole, for positioning, formed in the drilling plate4or another drilling jig.

Since the drilling plate4should have a structure to be easily placed depending on the structure of the workpiece W, it is often appropriate that the drilling plate4is produced by a user of the drilling unit1. Therefore, the drilling unit1may be composed of the drill2and the guide bush3, without the drilling plate4being an element of the drilling unit1. The drilling plate4shown in the figures has a structure in which a through hole for inserting the guide bush3has been formed on a platy member. The guide bush3inserted into the through hole of the drilling plate4is fixed to the drilling plate4by a setscrew4A.

The workpiece W is a laminate material composed by overlapping three plate materials W1, W2, and W3. As a specific example, the workpiece W composed by overlapping the plate material W1made of CFRP (carbon fiber reinforced plastics), the plate material W2made of aluminum, and the plate material W3made of titanium can be an object to be drilled by the drilling unit1. As a matter of course, a laminate material, a simple platy portion, a block-shaped portion or the like, each made of a same material, such as a metal or a composite material, can be an object to be drilled by the drilling unit1.

The drill2has a body5, without a back taper, and a cutting edge part6forming the desired number of cutting edges. The drill2held by a handheld drill driving device or the like is also called a drill bit in order to distinguish from a drill driving device. One end of the body5is used as a shank5A for holding the drill2with a holder of a drill driving device while the other end of the body5is integrated with the cutting edge part6. At least the cutting edge part6side of the body5without a back taper has a constant diameter, and is inserted into the guide bush3.

In the example shown inFIG. 1, the diameter of the cutting edge part6is longer than the diameter of the body5. Therefore, the guide bush3has a cylindrical structure having a step through hole consisting of the first hole, having the first diameter, which guides the cutting edge part6in the workpiece W side, and the second hole, having the second diameter smaller than the first diameter, which guides the body5on the opposite side of the workpiece W.

Since the guide bush3is used by being inserted into a through hole for positioning formed in the drilling plate4or the like, the outline of the guide bush3in the workpiece W side is determined so that the tolerance between the outline of the guide bush3in the workpiece W side and the diameter of the through hole for positioning formed in the drilling plate4or the like become a tolerance corresponding to clearance fit.

When a ring-shaped convex portion is formed on an outer surface of the guide bush3, the guide bush3can be positioned in the tool axis direction by making a ring-shaped stepped surface, perpendicular to the tool axis direction, contact with a surface of the drilling plate4or the like, as shown in the figures. Furthermore, the guide bush3can be fixed to the drilling plate4by holding the ring-shaped convex portion of the guide bush3between the setscrew4A and the drilling plate4, as shown in the figures.

The cutting edges of the drill2may be attached to the cutting edge part6interchangeably. A drill whose cutting edge can be exchanged as an insert or a head is also called an insert drill. When the drill2is an insert drill, the body5and a portion of the cutting edge part6except the cutting edges also function as a holder for holding each cutting edge interchangeably.

A two flute insert, which has been on the market for conventional insert drills, can also be used as an insert for the drill2. Therefore, the drill2may be composed of the body5and the cutting edge part6having a structure, in which each cutting edge can be attached while an existing general-purpose insert may be used as the cutting edges.

The diameter of the end portion in the holder side of the body5, which is not inserted in the guide bush3, may be larger than not only the inside diameter of the guide bush3but the diameter of the cutting edge part6in order to secure rigidity. In other words, another connecting member, such as the shank5A or a screw, thicker than the diameter of the body5may be coupled to the holder side of the body5. In that case, the drill2is a non-straight drill in which the diameter of the cutting edge part6is larger than the diameter of the body5in the cutting edge part6side. Also in that case, the diameter of a portion of the body5in the cutting edge part6side, which is used by being inserted in the guide bush3, is constant.

Regardless of the diameter of the shank5A, it is appropriate to form a flute or flutes for discharging chips in the cutting edge part6side of the body5. For example, helical flutes can be formed in the cutting edge part6side of the body5similarly to a twist drill. Alternatively, linear flutes may be formed in the cutting edge part6side of the body5similarly to a straight fluted drill.

The length of a portion of the body5, having a constant diameter without a back taper, is determined so that the drill2can be fed out in the tool axis direction. Therefore, the longer the length of the portion of the body5without a back taper is, the longer a distance that the drill2can be fed out in the tool axis direction can be. Accordingly, the diameters of the body5, including a portion used as the shank5A for holding with a holder, may be constant as shown in the figures.

As a matter of course, not only limited to the examples shown in the figures, the diameter of the cutting edge part6may be same as the diameter of the body5to compose a straight drill, or the cutting edge part6and the body5may be made of a same material to compose a solid type drill. Also in that case, the cutting edge part6side of the body5does not have a back taper, and a tool diameter is constant.

When the drill2is an insert drill as described above, the price of the drill2can be reduced since only a cutting edge made of an expensive material, such as carbide or ceramics, can be exchanged when the cutting edge is worn while the body5is made of a cheap material, such as high-speed steel, similarly to the conventional insert drill. Since there are few straight drills without a back taper in recent years, to manufacture a straight drill newly requires large scale equipment. By contrast, since a holder for an insert drill whose diameter of cutting edge is larger than the diameter of the holder does not contact with a workpiece, a holder without a back taper has also been marketed. Therefore, when the drill2is an insert drill, the drill2can be manufactured using the conventional equipment as much as possible.

At least one flow path7of a cutting oil is formed inside the body5. The cutting oil is supplied to the flow path7in the body5from the holder side of the body5. Therefore, it is practical to form an entrance of cutting oil on an end face in the holder side of the body5. In the example shown in the figures, the linear flow path7of cutting oil has been formed on the tool axis of the body5whose diameter is constant. In this case, the body5has a cylindrical structure.

Note that, the flow path7of the cutting oil may be formed at a position which is not on the tool axis of the body5. Alternatively, a plurality of the flow paths7, parallel to the tool axis, may be formed in the body5.

The cutting oil supplied to the flow path7in the body5is mainly supplied from the cutting edge part6to the workpiece W through the flow path7in the body5. Therefore, at least one outlet of the cutting oil is formed in the cutting edge part6. Each outlet of the cutting oil is used as the first supply port8A for supplying the cutting oil toward the workpiece W from the tip of the drill2. In the example shown in the figures, the four first supply ports8A have been formed in the cutting edge part6of the drill2.

Furthermore, some of the cutting oil supplied to the flow path7in the body5is supplied to a space formed between the guide bush3and the body5. Then, the cutting oil supplied to the space is used for lubrication between the guide bush3and the body5. For that purpose, the body5has the second supply port8B or the second supply ports8B for supplying the cutting oil to the gap formed between the guide bush3and the body5.

Accordingly, the flow path7of the cutting oil can be branched to the first flow paths7A and the second flow paths7B inside the drill2. Thus, the cutting oil can be supplied to the first supply ports8A through the first flow paths7while the cutting oil can be supplied to the second supply ports8B through the second flow paths7B. Thereby, the structure of the body5can be simplified with one entrance of the cutting oil into the body5.

It is appropriate to open each second supply port8B on the outer periphery of the body5in order to supply sufficient amount of the cutting oil to the clearance gap formed between the guide bush3and the body5. In particular, it is appropriate to form the second flow paths7B and the second supply ports8B so that the central axes of holes, which forms the second flow paths7B and the second supply ports8B, are directed toward interior surface of the guide bush3.

Therefore, for example, the second supply port8B can be opened on the outer periphery of the body5by forming the flow path7parallel to the tool axis and branching the second flow path7B in the direction perpendicular to the tool axis. When the central axis of the second flow path7B is made perpendicular to the tool axis, processing for forming the second flow path7B in the body5becomes easy.

Alternatively, the second flow path7B oblique toward the workpiece W side may be formed in the body5so that the cutting oil promptly permeates the workpiece W side through the clearance formed between the guide bush3and the body5. Therefore, the second flow path7B can also be formed in the body5so that an angle formed between the central axis of the second flow path7B and the tool axis becomes not less than 10 degrees and not more than 90 degrees. When flutes for discharging chips are formed in the body5, the second supply port8B may be opened in a flute or in a margin portion formed between the flutes.

As long as oil film of the cutting oil is formed, lubrication between the guide bush3and the body5can be fully obtained. On the other hand, the cutting oil supplied toward the workpiece W from the first supply ports8A formed in the cutting edge part6is used for the purpose of discharging chips, reducing cutting resistance, cooling or the like.

Therefore, while most of the cutting oil is supplied to the workpiece W from the first supply ports8A, supplying a minute amount of the cutting oil to the second supply port8B or the second supply ports8B leads to effective use of the cutting oil. Accordingly, it is preferable to form the flow paths7inside the body5so that the quantity of the cutting oil supplied to the second supply port8B or the second supply ports8B is less than the quantity of the cutting oil supplied to the first supply ports8A. For that reason, the single second supply port8B may be formed as shown in the figures, for example. Thereby, the structure of the body5can be simplified with allocating appropriate amounts of the cutting oil. Note that, a plurality of the second supply ports8B may be formed on the body5in order to obtain a sufficient amount of supply of the cutting oil to the space between the guide bush3and the body5regardless of drilling conditions.

When the workpiece W is drilled by the drill2, the drill2is fed out in the tool axis direction with making the body5slidably fit to the guide bush3as shown inFIG. 2. Therefore, a relative position of the second supply port8B to the guide bush3changes. It is desirable to supply the cutting oil to the space formed between the guide bush3and the body5at the latest by the time drilling starts, i.e., until the cutting edges of the drill2contact the workpiece W.

For that reason, the second supply port8B can be formed at the position where the second supply port8B opens inside the guide bush3in the state that the cutting edge part6is not protruding from inside the guide bush3as exemplified inFIG. 1. Thereby, the cutting oil can be certainly supplied between the guide bush3and the body5before drilling starts.

When the feeding amount of the drill2is longer than the length of the portion of the guide bush3, which slidably fits the body5, the second supply port8B is exposed outside the portion of the guide bush3, which slidably fits the body5, as exemplified inFIG. 2. Nevertheless, the lubricity between the guide bush3and the body5can be maintained since oil film of the cutting oil remains between the guide bush3and the body5once the cutting oil is supplied between the guide bush3and the body5.

What is necessary in order to direct the second supply port8B inside the guide bush3which slidably fits the body5as much as possible after applying a feed to the drill2is to form the second supply port8B at a position where the second supply port8B opens at the end portion inside the guide bush3on the opposite side to the workpiece W at the time when the tip of the cutting edge part6has contacted the workpiece W. Therefore, when a gap is formed between the guide bush3and the workpiece W as shown in the figures, a position of the second supply port8B may be determined in consideration of a distance between the guide bush3and the workpiece W.

A drilled product can be manufactured by drilling the workpiece W with supplying the cutting oil using at least the drill2and the guide bush3which have the above-mentioned structures.

As described above, the drilling unit1and the drilling method use the drill2, used by being inserted in the guide bush3, without a back taper and having at least one oil hole for supplying a cutting oil between the guide bush3and the drill2.

Effects

According to the drilling unit1and the drilling method, the accuracy in drilling can be improved. The reason is as follows.

FIG. 3shows an example case of drilling using the conventional straight drill10having a back taper and the guide bush11.

The typical drill10has a back taper. The back taper is formed so that the drill10does not contact with inner walls of a hole even when the drill10expands with heat during drilling. The back taper is standardized, and the taper which becomes thin toward the direction of a shank is formed in the drill10so that the diameter of the drill10is thinned by 0.04 mm to 0.1 mm per 100 mm in length.

On the other hand, in the case of using the guide bush11with inserting the drill10, the more the drill10is fed out to the workpiece W, the larger the gap between the drill10and the guide bush11becomes. As a result, the accuracy of positioning of the drill10deteriorates and it leads to the degradation of a drilling accuracy.

On the contrary, in the case of the drill2without a back taper, even when the drill2is fed out with guiding by the guide bush3, the gap between the drill2and the guide bush3does not become larger. In addition, cutting oil is supplied as lubricating oil between the drill2and the guide bush3. Therefore, the frictional force between the drill2and the guide bush3can be reduced fully. As a result, even when the drill2without a back taper expands with heat, transmission fit between the drill2and the guide bush3is maintainable. Thereby, the deterioration in the accuracy of positioning of the drill2can be prevented and drilling quality can be improved.

As mentioned above, candidates of a material of the workpiece W, for which drilling quality can be improved, include a metal, such as aluminum or titanium, a composite material, such as CFRP, which consists of a resin reinforced with a fiber and a laminate material which consists of overlapped metal and composite material.

FIG. 4is an enlarged vertical longitudinal sectional view showing a structure of a body composing a drill according to the second implementation of the present invention.FIG. 5is a right side view of the body shown inFIG. 4.

The drilling unit1A in the second implementation shown inFIG. 4is different from the drilling unit1in the first implementation in the point that the second flow path7B formed in the body5composing the drill2is made exchangeable. Other structures and functions of the drilling unit1A in the second implementation does not substantially differ from those of the drilling unit1in the first implementation. Therefore, only the body5composing the drill2is illustrated. Then, same signs are attached to the same elements and corresponding elements and explanation thereof is omitted.

As shown inFIG. 4andFIG. 5, a through hole having a diameter larger than that of the second flow path7B can be formed at the position of the body5at which the second flow path7B should be formed, and a female screw can be formed inside the through hole. On the other hand, a cylindrical member20of which outer surface forms a male screw and which has the second flow path7B along the center can be fastened to the female screw formed in the through hole of the body5. That is, the cylindrical member20in which the second flow path7B is formed can be inserted into the through hole which has been formed in the body5.

Then, the member20can be detached and attached from and to the body5of the drill2. In the example shown inFIG. 4andFIG. 5, a groove for a flat-bladed screwdriver is formed in the end surface in the outside of the member20so that the member20can be easily detached from and attached to the body5of the drill2.

Thereby, preparing the members20in which the second flow paths7B and the second supply ports8B having diameters D different from each other have been formed allows changing the size of the second flow path7B and the second supply port8B by exchanging one of the members20with another one. In this case, any one of the members20forming the second supply ports8B and the second flow paths7B in different sizes respectively is to be attached to the body5of the drill2so that the member20can be exchanged.

As a specific example, the member20of which the diameter D of the second flow path7B and the second supply port8B is 0.5 mm and the member20of which the diameter D of the second flow path7B and the second supply port8B is 1 mm may be prepared, and one of them can be chosen in accordance with the drilling conditions. As a matter of course, the member20in which the second flow path7B and the second supply port8B having another diameter D have been formed may be prepared.

When the diameter D of the second flow path7B and the second supply port8B is determined to an appropriate size in accordance with the drilling conditions, the cutting oil supplied to the flow path7of the body5from a drill driving device can be distributed to the first flow paths7A and the second flow path7B with appropriate amounts. Specifically, supplying an excess quantity of the cutting oil to the gap between the guide bush3and the body5from the second supply port8B can be prevented while supplying an insufficient quantity of the cutting oil to the gap between the guide bush3and the body5from the second supply port8B can be prevented.

The important drilling conditions which should be taken into consideration in determining the diameter D of the second flow path7B and the second supply port8B as an appropriate size include a cutting resistance and an oil pressure of the cutting oil supplied to the drill2from a drill driving device. Specifically, when the oil pressure of the cutting oil supplied to the body5of the drill2from a drill driving device is high enough, sufficient quantity of the cutting oil can be injected towards the workpiece W from the first supply ports8A even when the cutting resistance is large. On the contrary, when the diameter D of the second flow path7B and the second supply port8B is set excessively large in the case where the oil pressure of the cutting oil supplied to the body5of the drill2from a drill driving device is low and the cutting resistance is large, an excess amount of the cutting oil may be supplied to the gap between the guide bush3and the body5from the second supply port8B while the amount of the cutting oil supplied from the first supply ports8A to the workpiece W may become insufficient.

As main conditions which influence to the cutting resistance, a depth of hole to be drilled, a material of the workpiece W, and a material of cutting edges are mentioned. That is, the cutting resistance changes in accordance with a depth of hole to be drilled, a material of the workpiece W, and a material of the cutting edges. Accordingly, the diameter D of the second flow path7B and the second supply port8B can be changed in accordance with a pressure of the cutting oil supplied from a drill driving device to the drill2, a depth of hole to be drilled, a material of the workpiece W, and a material of the cutting edges.

More specifically, when the cutting resistance is small and a supply pressure of the cutting oil from a drill driving device is high, the diameter D of the second flow path7B and the second supply port8B can be made large so that a sufficient quantity of the cutting oil can be led from the second flow path7B and the second supply port8B to the gap between the guide bush3and the body5. On the contrary, when the cutting resistance is large and the supply pressure of the cutting oil is low, the diameter D of the second flow path7B and the second supply port8B can be made small so that most part of the cutting oil is prevented from being supplied from the second flow path7B and the second supply port8B to the gap between the guide bush3and the body5while the amount of the cutting oil supplied from the first supply ports8A to the workpiece W can be secured.

Some drilling examinations can experientially determine a size of the second flow path7B and the second supply port8B appropriate for every conditions, such as a pressure of the cutting oil supplied from a drill driving device to the drill2, a depth of hole to be drilled, a material of the workpiece W and a material of the cutting edges.

According to the above-mentioned drilling unit1A in the second implementation, the size of the second flow path7B and the second supply port8B for supplying the cutting oil to the space between the guide bush3and the body5can be adjusted. Thereby, the cutting oil supplied from a drill driving device to the drill2can be distributed to a part to be drilled of the workpiece W, and the space between the guide bush3and the body5with adequate amounts.

When flutes for discharging chips are formed in the body5of the drill2, the second flow path7B and the second supply port8B may be formed on a flute or a margin of the body5, similarly to the first implementation. Therefore, the through hole and the female screw for inserting the member20can also be formed on a flute or margin of the body5. Then, the member20can be attached to the flute or margin of the body5.

FIG. 6shows a structure of a drilling unit including a drill according to the third implementation of the present invention.FIG. 7shows a state where the drilling unit shown inFIG. 6is drilling a workpiece.

The drilling unit1B in the third implementation shown inFIG. 6is different from the drilling unit1A in the second implementation in the point that members20each forming the second flow path7B and the second supply port8B can be attached at positions different in the tool axis direction of the drill2. Other structures and functions of the drilling unit1B in the third implementation does not substantially differ from those of the drilling unit1A in the second implementation. Therefore, same signs are attached to the same elements and corresponding elements and explanation thereof is omitted.

As shown inFIG. 6, the through holes and the female screws for inserting the members20, each forming the second flow path7B and the second supply port8B, may be formed at plural positions of the body5different in the tool axis direction. Then, the second flow paths7B and the second supply ports8B can be formed at different positions in the tool axis direction of the drill2. In the example shown inFIG. 6, the members20are respectively attached to two different positions of the body5in the tool axis direction so that the members20can be attached and detached to and from the body5.

When the second flow paths7B and the second supply ports8B are formed at different positions in the tool axis direction, even after the second supply port8B closest to the cutting edge part6has been exposed from the space between the guide bush3and the body5, to which the cutting oil should be supplied, because of the progression of drilling the workpiece W, the cutting oil can be continuously supplied to the space between the guide bush3and the body5from another second supply port8B formed at a different position in the tool axis direction. Consequently, the length of the body5which can be fed out in the tool axis direction toward the workpiece W with sliding fit to the guide bush3by supply of the cutting oil can be increased. As a result, a deep hole can be drilled using the guide bush3as shown inFIG. 7.

Therefore, the distance between the adjacent second supply ports8B can be determined according to a length of the guide bush3to which lubricity to the body5should be given. As explained in the first implementation, the cutting oil discharged out from each second supply port8B remains as an oil film, during a certain length of period, on the surface of the body5and inside of the guide bush3. Accordingly, it is appropriate to determine the distance between the adjacent second supply ports8B so that an oil film may not break off between the guide bush3and the body5even when the body5is slid relative to the guide bush3by sending out the drill2in the tool axis direction.

When it is a case where reducing the number of the members20is thought as important, the second supply ports8B can be arranged at an interval at which an oil film would not break off between the guide bush3and the body5. As a concrete example, the distance between the second supply ports8B can be determined so that the cutting oil discharged out from the second supply port8B adjacent the shank5A side of the body5may arrive at the space, to which the cutting oil should be supplied, between the guide bush3and the body5through the body5before the second supply port8B in the cutting edge part6side is exposed from the space between the guide bush3and the body5.

Alternatively, when it is a case where ensuring the lubricity between the guide bush3and the body5is thought as important, the distance between the second supply ports8B can be determined so that the second supply port8B adjacent the shank5A side of the body5may arrive at the space, to which the cutting oil should be supplied, between the guide bush3and the body5before the second supply port8B in the cutting edge part6side is exposed from the space between the guide bush3and the body5, for example. That is, the distance between the second supply ports8B can be determined to not more than the length in the tool axis direction of the space, to which the cutting oil should be supplied, between the guide bush3and the body5, i.e., the length of the guide bush3which slidingly fits to the body5.

On the other hand, it is enough to form the single second supply port8B in the same position in the tool axis direction, as explained in the first implementation. Accordingly, forming the single second supply port8B in the same position in the tool axis direction leads to simplification of the structure of the drill2and reduction of a manufacturing cost of the drill2. Nevertheless, the number of the second supply ports8B formed in the same position in the tool axis direction may be more than one in order to obtain a sufficient amount of supply of a cutting oil to the space between the guide bush3and the body5regardless of drilling conditions.

In the case of enabling it to form the second supply ports8B at different positions in the tool axis direction, the second supply port B in the shank5A side of the body5may become unnecessary for drilling a shallow hole. Accordingly, a plug member for blockading the second flow path7B and the second supply port8B may be inserted to the through hole and the female screw which have been formed in the body5, instead of the member20for forming the second flow path7B and the second supply port8B.

FIG. 8is a longitudinal sectional view of the body5showing an example case where the through hole for inserting the member20shown inFIG. 6is blockaded with the plug member21.

As exemplified inFIG. 8, when the columnar plug member21of which a male screw has been formed on the outer circumference is produced, the plug member21can be attached and detached to and from the body5. Thereby, the second flow path7B and the second supply port8B can be blockaded by fastening the male screw of the plug member21to the female screw formed in the through hole for insertion of the member20, as necessary, such as a case of drilling a shallow hole. As a result, supply of useless cutting oil can be reduced.

The plug member21which blockades the second flow path7B and the second supply port8B can be also used to the drill2in the second implementation. When the second flow path7B and the second supply port8B which can be formed in the drill2in the second implementation are blockaded by the plug member21, the drill2can be used even in the case of drilling without using the guide bush3. Namely, flexibility can be given to the drill2.

Next, an example case where the drilling unit1B is composed by an insert drill of which cutting edges can be exchanged will be described.

FIG. 9is a longitudinal sectional view showing an example case where the drilling unit1B is composed by an insert drill2A of which body5has helical flutes and cutting edges can be exchanged.FIG. 10is a longitudinal sectional view showing a state where the drilling unit1B shown inFIG. 9is drilling a workpiece W.FIG. 11is an enlarged vertical longitudinal sectional view near the tip of the insert drill2A shown inFIG. 9.FIG. 12is a longitudinal sectional view showing an example of structure in the cutting edge part6A of the insert drill2A shown inFIG. 9.

As exemplified inFIG. 9toFIG. 12, the drilling unit1B can be composed of the insert drill2A. The structure of the cutting edge part6A of the insert drill2A can be made to the structure in which the width of the slit31can be changed by fastening the bolt30as shown inFIG. 12, for example. Specifically, when the bolt30is fastened to make the width of the slit31narrow, the cutting edge32can be inserted and held by the cutting edge part6A. On the contrary, when the bolt30is loosened to make the width of the slit31expanded, the cutting edge32can be removed from the cutting edge part6A.

Such structure of the cutting edge part6A including one having oil holes is already put into practical use, and can be manufactured easily. Then, the drilling unit1B can be configured by the insert drill2A of which the cutting edge part6A and the body5function as a holder of the cutting edge32.

In the example shown inFIG. 9andFIG. 10, the body5of the insert drill2A on which helical flutes have been formed has the six second flow paths7B and the six second supply ports8B. Specifically, the two second flow paths7B and the two second supply ports8B are formed at each of three positions different in the tool axis direction. Accordingly, a deep hole can be processed using the insert drill2A. The second flow path7B and the second supply port8B can be formed in any of a flute portion and a margin portion, as exemplified inFIG. 9andFIG. 10.

The insert drill2A can be used with being attached to a handheld drill driving device40. In the example shown inFIG. 9andFIG. 10, the male screw2B is formed in the back end side of the insert drill2A so that the male screw2B of the insert drill2A is fasten to the female screw41which has been formed in the handheld drill driving device40, thereby the insert drill2A is held by the drill driving device40.

The drill driving device40has the cylindrical nosepiece42which shields the insert drill2A, and the nosepiece42is connected with the guide bush3. Specifically, the male screw which has been formed on the external surface of the guide bush3is fastenable to the female screw which has been formed inside of the tip side of the nosepiece42, thereby the nosepiece42is connected with the guide bush3.

Therefore, not only the insert drill2A and the guide bush3but the handheld drill driving device40having the nosepiece42which has a structure connectable to the guide bush3may be an element of the drilling unit1B. This is the same in the first implementation and the second implementation.

According to the drilling unit1B in the above mentioned third implementation, the second flow paths7B and the second supply ports8B can be formed at different positions in the tool axis direction of the drill2so that a deep hole can be processed. Moreover, the second flow path7B and the second supply port8B can also be blockaded by the plug member21so that a shallow hole can also be processed.

FIG. 13is a perspective view showing the first structural example of a member inserted into at least one through hole formed in a body of a drill according to the fourth implementation of the present invention.FIG. 14is a perspective view showing the second structural example of a member inserted into at least one through hole formed in a body of a drill according to the fourth implementation of the present invention.

The drilling unit1C in the fourth implementation shown inFIG. 13orFIG. 14is different from each of the drilling unit1, the drilling unit1A and the drilling unit1B in the other implementations in the point that the respective pressure losses of the second flow paths7B formed in the body5of the drill2are determined so that the cutting oil may be exuded from the second supply ports8B formed on the outer peripheral surface of the body5as the outlets of the second flow paths7B respectively without being scattered from the second supply ports8B in the radial direction of the body5. Other structures and functions of the drilling unit1C in the fourth implementation do not substantially differ from those of the drilling unit1, the drilling unit1A and the drilling unit1B in the other implementations. Therefore, only a member20A, a member20B and a member20C each forming the second flow path7B are illustrated. Then, the same signs are attached to the same elements and the corresponding elements, and explanation thereof is omitted.

The pressure loss of each second flow path7B becomes larger as the area of the cross section is smaller since the frictional resistance with the cutting oil increases. Thus, the cross section area of at least a part of each second flow path7B can be determined so that the pressure loss of the second flow path7B becomes one with which the cutting oil is exuded without being scattered from the second supply port8B in the radial direction of the body5.

As a practical example, the pressure loss of each second flow path7B can be increased by inserting the column-shaped member20A, made of a porous material as exemplified inFIG. 13, in a hole reaching the first flow path7A from the outer surface of the body5. Specifically, forming at least a part of each second flow path7B with a porous material makes it possible to make the pressure loss of each second flow path7B be a pressure loss by which the cutting oil is not scattered from the second supply port8B in the radial direction of the body5but exuded from the second supply port8B.

Concrete examples of porous material include porous aluminum in addition to felt (a non-woven fabric), pumice stone and the like. In particular, when porous aluminum of which workability and wear resistance are preferable is used, it becomes easy to produce the member20A, which forms the second flow path7B, and attach the member20A to the body5.

As another concrete example, the member20B forming the second flow path7B whose cross section area has been adjusted as exemplified inFIG. 14may also be inserted in each through hole formed in the body5, similarly to the second implementation. AlthoughFIG. 14shows an example case where a slit having a rectangular cross section has been formed, as the second flow path7B, in the member20B, the second flow path7B having a circular cross section may be formed in the member20B. Alternatively, the second flow path7B having an adjusted cross section area may be formed directly in the body5, similarly to the first implementation.

When a male screw is formed in the outer surface of the member20B and fastened to a female screw formed in each through hole of the body5, similarly to the second implementation, the member20B forming the second flow path7B can be exchanged. Therefore, the plurality of the members20B respectively forming the second flow paths7B having pressure losses different from each other may be prepared so that one of the members20B can be interchangeably attached to the body5. When a slit is the second flow path7B as exemplified inFIG. 14, a direction of the slit may also be changed. Accordingly, a direction of a slit and/or the size of the second flow path7B may be changed according to cutting conditions, such as a supply pressure and a kind of the cutting oil, the size and rotation speed of the drill2, a material of the workpiece W and a depth of a hole to be drilled.

Some actual drilling examinations under various conditions revealed the following fact. A condition that the maximum width of the cross section of at least a part of the second flow path7B is not more than 0.5 mm is important in order to prevent the cutting oil from scattering from the second supply port8B in the radial direction of the body5even when the body5is rotated while the cutting oil is supplied to the flow path7in the body5. Therefore, it is appropriate that each second flow path7B is a small clearance of which inside diameter or width is about not more than 0.5 mm.

For that reason, the columnar member20which is not hollow and has a male screw on the outer surface, like the plug member21shown inFIG. 8, may be fastened to a female screw formed in each through hole of the body5so that a clearance formed between the male screw formed on the columnar member20and the female screw formed in each through hole of the body5can be used as the second flow path7B.

FIG. 15is an enlarged partial sectional view of the body5and the columnar member20C, showing an example in which a clearance formed between a male screw and a female screw is used as the second flow path7B.

As shown inFIG. 15, a male screw50A can be formed on the outer surface of the columnar member20C while a female screw50B can be formed in each through hole of the body5. When the male screw50A formed on the columnar member20C is fastened to the female screw50B formed in a through hole of the body5, a clearance, called a crest clearance of the male screw50A, is formed between the thread of the male screw50A and the root of the female screw50B while a clearance, called a root clearance of the male screw50A, is formed between the root of the male screw50A and the thread of the female screw50B, as long as tolerance classes of the male screws50A and the female screw50B are typical respectively.

Accordingly, each of the clearances formed between the male screw50A and the female screw50B can be used as the second flow path7B for discharging and exuding the cutting oil from the body5. In this case, the second flow path7B become spiral and the width of the second flow path7B can be adjusted by selecting tolerance classes of a male screw and a female screw which classify fitting between the male screw and the female screw into classifications including precise, middle and rough.

On the contrary, when the second flow path7B is blockaded by the plug member21shown inFIG. 8, it is important to adopt a specification of a pair of screws in which a clearance from which the cutting oil may leak is not generated between the male screw formed on the plug member21and the female screw formed in each through hole of the body5, similarly to a case using a pipe thread.

In addition to the above-mentioned example, at least one of central axes of the second flow paths7B may be slanted in the workpiece W side so that the cutting oil may be discharged not in the rotating radial direction of the body5but toward the workpiece W side. Moreover, it is experientially important to form the flow paths7so that the amount of the cutting oil supplied to the first supply ports8A formed as the outlets of the first flow paths7A respectively becomes not less than twice the amount of the cutting oil supplied to the second supply ports8B formed as the outlets of the second flow paths7B respectively, from a viewpoint of avoiding shortage in the cutting oil which should be supplied to the first flow paths7A and the first supply ports8A, as a result that an excess amount of the cutting oil has been supplied to the second flow paths7B and the second supply ports8B.

According to the drilling unit1C in the above-mentioned fourth implementation, it can be prevented that an excess amount of the cutting oil is supplied to the second flow paths7B and the second supply ports8B. As a result, it becomes possible to prevent the cutting oil from scattering from the second supply ports8B which have been exposed to the outside of the guide bush11. Alternatively, the amount of the cutting oil scattering from the second supply ports8B which have been exposed to the outside of the guide bush11can be reduced.

On the other hand, a sufficient amount of the cutting oil can be supplied to the first flow paths7A and the first supply ports8A. That is, a pressure of the cutting oil supplied to the first flow paths7A and the first supply ports8A can be secured since a pressure loss due to scattering of the cutting oil from the second supply ports8B can be remarkably reduced.

Moreover, cleaning work after drilling of the workpiece W becomes easy since the cutting oil scattering from the second supply ports8B can be eliminated or at least an amount of the cutting oil scattering from the second supply ports8B can be decreased.