Patent Description:
A core drilling machine is a mechanical apparatus for drilling a hole into a wall, a ceiling, etc. upon piping construction in a building. Generally, such a core drilling machine constitutes a core drill assembly together with various devices configured to manipulate a core drill.

A general core drill assembly, which is currently used, includes a base fixed to a structure, into which a hole is to be drilled, by an anchor bolt, a stand disposed to be perpendicular to the base and formed with a rack at one side surface thereof, a driving body with a pinion mounted therein, the driving body being vertically reciprocable along the stand in accordance with a rotating operation of a handle, and a core drill mounted to the driving body and configured to drill a hole into a particular portion of the structure. Here, the core drill is constituted by a core bit configured to drill a hole into the structure through frictional contact between the core bit and the structure, and a drive motor configured to rotate the core bit at a high speed.

The core drill assembly having the above-mentioned configuration operates as follows. When the handle installed at the driving body is rotated in a state in which the base is fixed to a wall or a bottom surface of the structure using a plurality of anchor bolts, the pinion of the driving body, which engages with the rack of the stand, moves along the rack. As a result, the driving body reciprocates vertically along the stand. In this state, when electric power is applied to the drive motor, the core bit is rotated. The core bit, which rotates at a high speed, drills a hole into the structure while moving forwards.

However, such a conventional core drilling machine performs drilling using only one core bit mounted thereto. For this reason, for drilling of a plurality of holes, the core drilling machine should be moved to hole positions one by one, and tasks for fixing the core drilling machine using anchor bolts and drilling a hole should be performed for the hole positions one by one. As a result, there are problems in that work is troublesome, and a lot of time is taken.

In particular, in a working environment in a large-scale factory requiring rapid drilling of a number of holes, use of only the conventional core drilling machine may cause a problem in that high costs are taken because a number of workers should be committed, in addition to a problem of an increased working time. <CIT> describes a drilling machine, particularly a core drilling machine, that includes a stand. A carriage is guided by the stand so as to move toward the working direction along a guide by means of a driving section. A drilling unit having a spindle to be driven by a motor is received in the carriage to drive a drill. A driving section includes a stepper motor. <CIT> discloses a two-hole core drilling machine as per the preambles of appended claims <NUM> and <NUM>.

The present invention proposes alternative two-hole core drilling machines.

It is an object of the present invention to provide an alternative two-hole core drilling machine.

In accordance with an aspect of the present invention, the above and other objects can be accomplished by the provision of a two-hole core drilling machine including a body, a vertically reciprocating carriage vertically reciprocably mounted to the body, a fixing plate coupled to one side surface of the carriage, to rotatably support a drive shaft of a motor, a pivoting plate fastened to the fixing plate, a pivot angle of the pivoting plate is changeable; a moving plate fastened to the pivoting plate, a length of the moving plate from the pivoting plate is variable; a belt or chain mounted between a drive pulley coupled to the drive shaft and a driven pulley coupled to a driven shaft rotatably mounted to the moving plate, a first core bit coupled to the drive shaft, and a second core bit coupled to the driven shaft. The body may include a base fixed to a structure to be drilled, and a stand vertically coupled to the base and formed with a gear at one side surface thereof. The carriage may be provided with a pinion engaged with the gear, and may be vertically reciprocably mounted to the stand. The fixing plate may include a pivot guide slit formed through the fixing plate while having an arc shape. The pivoting plate may include a plurality of fastening holes formed to extend vertically through the pivoting plate. The pivoting plate may be fixed at a predetermined pivot position with respect to the fixing plate by fasteners fastened to the plurality of fastening holes and the pivot guide slit. The pivoting plate may include a movement guide slit formed lengthily in a longitudinal direction. The moving plate may include a plurality of fastening holes formed to extend vertically through the moving plate. The moving plate may be fixed at a predetermined position in a longitudinal direction with respect to the pivoting plate by fasteners fastened to the plurality of fastening holes and the movement guide slit. The moving plate may further include a tension roller configured to be fixed after a rotation shaft of the tension roller moves toward the belt or chain loosened in accordance with movement of the moving plate, thereby applying tension to the belt or chain. Water supply hoses may be connected to lower portions of the drive shaft and the driven shaft, respectively, to supply cooling water. The gear may include a rack.

In accordance with another aspect of the present invention, there is provided a two-hole core drilling machine including a body, a vertically reciprocating carriage vertically reciprocably mounted to the body, a fixing plate coupled to one side of the carriage, to rotatably support a drive shaft of the motor, a pivoting plate fastened to the fixing plate, a pivot angle of the pivoting plate is changeable; a moving plate fastened to the pivoting plate, a distance of the moving plate from the fixing plate is variable, a driven shaft being rotatably mounted to the moving plate, a gear train coupled between the drive shaft and the driven shaft, to transmit rotation force of the drive shaft to the driven shaft, a first core bit coupled to the drive shaft, and a second core bit coupled to the driven shaft.

The body may include a base fixed to a structure to be drilled, and a stand vertically coupled to the base and formed with a gear at one side surface thereof. The carriage may be provided with a pinion (for example, a hydraulic cylinder) (for convenience of description, referred to as a "pinion") engaged with the gear, and may be vertically reciprocably mounted to the stand. The fixing plate may include a plurality of fastening holes arranged on a circumference having a predetermined radius from the drive shaft. The pivoting plate may include a plurality of fastening holes extending vertically through the pivoting plate. The pivoting plate may be fixed at a predetermined pivot position with respect to the fixing plate by fasteners fastened through the plurality of fastening holes of the fixing plate and the plurality of fastening holes of the pivoting plate. The pivoting plate may include a plurality of slots lengthily formed in a longitudinal direction. The moving plate may include a plurality of fastening holes formed to extend vertically through the moving plate. The moving plate may be fixed at a predetermined position in a longitudinal direction with respect to the pivoting plate by fasteners fastened to the plurality of fastening holes and the plurality of slits. The gear train may include a first link bracket pivotably mounted to the drive shaft, a second link bracket pivotably connected, at one end thereof, to the first link bracket while being pivotably mounted, at the other end thereof, to the driven shaft, a drive gear coupled to the drive shaft, to be rotatable by the drive shaft, a first intermediate gear mounted to the first link bracket while engaging with the drive gear, a second intermediate gear mounted to connection portions of the first link bracket and the second link bracket while engaging with the first intermediate gear, a third intermediate gear mounted to the second link bracket while engaging with the second intermediate gear, and a driven gear coupled to the driven shaft while engaging with the third intermediate gear, to be rotatable by the third intermediate gear. Water supply hoses may be connected to a middle portion of the drive shaft and an upper portion of the driven shaft, respectively, to supply cooling water. A guide groove configured to guide movement of the moving plate may be formed at an upper surface of the pivoting plate. A protrusion may be formed at a side surface of the moving plate, and a groove engaging with the protrusion may be formed in a longitudinal direction at the pivoting plate, to prevent separation of the moving plate.

In accordance with the two-hole core drilling machine of the exemplary embodiment of the present invention, it may be possible to simultaneously drill two holes by simultaneously rotating the two core bits.

In addition, in the two-hole core drilling machine of the exemplary embodiment of the present invention, the relative pivot angle between the two core bits and the distance between the two core bits may be adjusted and, as such, it may be possible to easily simultaneously drill two holes while appropriately adjusting the distance between the two holes to be drilled within a predetermined range.

Embodiments may be variously varied and may have various forms. In connection with this, specific embodiments will be illustrated in the drawings, and will be described in detail in the specification, but embodiments should not be construed as limited to the specific embodiments. It is to be appreciated that all changes, equivalents, and substitutes that do not depart from the scope of the appended claims are encompassed in the embodiments.

It should be noted that the terms used herein are merely used to describe a specific embodiment, not to limit the present invention. Incidentally, unless clearly used otherwise, singular expressions include a plural meaning.

It is noted that the same reference numerals in the drawings designate the same constituent elements, respectively. For similar reasons, in the accompanying drawings, a part of constituent elements is exaggerated, omitted, or schematically illustrated.

<FIG> is a perspective view schematically showing a two-hole core drilling machine according to an exemplary embodiment of the present invention. <FIG> is a front view schematically showing an inner structure of the two-hole core drilling machine according to the exemplary embodiment of the present invention.

The two-hole core drilling machine according to the exemplary embodiment of the present invention, which is designated by reference numeral "<NUM>", includes a base <NUM> fixed to a structure to be drilled (for example, a concrete floor, etc.), a stand <NUM> vertically coupled to the base <NUM> and formed with a gear (for example, a rack) <NUM> at one side surface thereof, a vertically reciprocating carriage <NUM> provided with a pinion engaged with the rack <NUM> and vertically reciprocably mounted to the stand <NUM>, a fixing plate <NUM> coupled to one side surface of the carriage <NUM>, to rotatably support a drive shaft <NUM> of a motor <NUM>, a pivoting plate <NUM> fastened to the fixing plate <NUM> under the condition that a pivot angle of the pivoting plate <NUM> is changed, and a moving plate <NUM> fastened to the pivoting plate <NUM> under the condition that an extension length of the moving plate <NUM> is varied. The two-hole core drilling machine <NUM> also includes a belt <NUM> mounted between a drive pulley <NUM> coupled to the drive shaft <NUM> and a driven pulley <NUM> coupled to a driven shaft <NUM> rotatably mounted to the moving plate <NUM>, a first core bit <NUM> coupled to the drive shaft <NUM>, and a second core bit <NUM> coupled to the driven shaft <NUM>.

Among the constituent elements of the two-hole core drilling machine <NUM> according to the exemplary embodiment of the present invention, the base <NUM> and the stand <NUM> may be collectively referred to as a "body".

The two-hole core drilling machine <NUM> is a core drilling machine configured to drill a hole into a horizontal bottom, a wall, or an inclined or curved surface having various shapes in a concrete structure.

The base <NUM> is provided with at least one pair of anchor bolts <NUM> therein and, as such, may be fixed to a surface of a structure. Although the anchor bolts <NUM> are shown in <FIG> as being disposed at opposite ends of the base <NUM>, a hole may be disposed at a central portion of the base <NUM>, and an anchor bolt <NUM> may be fixed to a surface of the structure through the hole. In addition, the base <NUM> is provided with at least one pair of wheels <NUM> and, as such, the entirety of the two-hole core drilling machine <NUM> may be easily movable.

The stand <NUM> is vertically coupled to the base <NUM>. The stand <NUM> may be formed to have a rectangular column shape. A connecting frame <NUM> may be coupled between a middle portion of the stand <NUM> and the base <NUM>, to support the stand <NUM> with respect to the base <NUM>. The rack <NUM> may be formed at one side surface of the stand <NUM>, to vertically reciprocate the carriage <NUM> mounted to the stand <NUM>.

The carriage <NUM> may be provided with the pinion (not shown) engaged with the rack <NUM> and, as such, may be vertically reciprocably mounted to the stand <NUM>. The carriage <NUM> may be provided with a lever <NUM> configured to rotate the pinion. Accordingly, upon operating the drilling machine <NUM>, the operator may rotate the lever <NUM>, thereby vertically reciprocating the carriage <NUM>. In addition, guide grooves <NUM> may be formed at opposite side surfaces of the stand <NUM>, respectively, to guide and support vertical reciprocation of the carriage <NUM>.

The motor <NUM> may be coupled to an upper portion of one side surface of the carriage <NUM>, and the fixing plate <NUM> may be coupled to a lower portion of the side surface of the carriage <NUM>. The motor <NUM> may be, for example, an electric motor, and the drive shaft <NUM> thereof may be rotatably supported by a bearing <NUM> mounted to the fixing plate <NUM>.

The pivoting plate <NUM> may be mounted to an upper surface of the fixing plate <NUM> such that the pivoting plate <NUM> is pivotable about the drive shaft <NUM>. The pivoting plate <NUM> may be fixed to the fixing plate <NUM> by a fastener under the condition that a pivot angle of the pivot plate <NUM> is changed.

In addition, the moving plate <NUM> may be mounted to an upper surface of a front portion of the pivoting plate <NUM> under the condition that a relative position of the moving plate <NUM> with respect to the pivoting plate <NUM> in a longitudinal direction is varied, in order to vary an extension length of the moving plate <NUM>. The driven shaft <NUM> may be rotatably mounted to the moving plate <NUM> by means of a bearing <NUM>.

The drive pulley <NUM> is coupled to the drive shaft <NUM>, and the driven pulley <NUM> is coupled to the driven shaft <NUM>. The belt <NUM> is connected to the drive pulley <NUM> and the driven pulley <NUM> and, as such, the motor <NUM> may simultaneously rotate the drive shaft <NUM> and the driven shaft <NUM>. In this case, the first core bit <NUM> is configured to be fixed, whereas the second core bit <NUM> may be configured to be rotatable in left and right directions such that the second core bit <NUM> has a desired rotation angle.

Meanwhile, a chain may be connected in place of the belt <NUM>. In this case, a drive sprocket and a driven sprocket may be connected to the chain, in place of the drive pulley <NUM> and the driven pulley <NUM>.

The first core bit <NUM> is coupled to a lower end of the drive shaft <NUM>, and the second core bit <NUM> is coupled to a lower end of the driven shaft <NUM>. The first core bit <NUM> and the second core bit <NUM> may have the same size. However, two core bits having various and different sizes, may be coupled to the drive shaft <NUM> and the driven shaft <NUM>, respectively.

In the two-hole core drilling machine <NUM> according to the exemplary embodiment of the present invention, the first core bit <NUM> and the second core bit <NUM> may be provided to be fixed in a state in which pivot angle positions of the first core bit <NUM> and the second core bit <NUM> with respect to the base <NUM> and a relative length between the first core bit <NUM> and the second core bit <NUM> are adjusted. Thus, the two-hole core drilling machine <NUM> may simultaneously drill two holes in a state in which a relative pivot angle and a relative length between the two holes are appropriately adjusted.

<FIG> is a top view showing a pivot angle and length adjusting structure of the two-hole core drilling machine. <FIG> is a top view showing a state in which the moving plate is coupled to the fixing plate after moving with respect to the fixing plate from a state of <FIG>.

The fixing plate <NUM> may be formed to take the form of a rectangular plate having an arc shape at one side thereof. Linear sides of the fixing plate <NUM> may be coupled to the carriage <NUM> and, as such, the fixing plate <NUM> may be vertically reciprocable together with the carriage <NUM>. A pivot guide slit <NUM> having an arc shape may be formed through the fixing plate <NUM> near an edge of the arc-shaped side of the fixing plate <NUM>.

The pivoting plate <NUM> may be mounted to the upper surface of the fixing plate <NUM> such that the pivoting plate <NUM> is pivotable about the drive shaft <NUM> concentric with the fixing plate <NUM>. The pivoting plate <NUM> may be formed to have a rectangular shape in which one side thereof facing the carriage <NUM> is formed to have an arc shape, and the other side thereof extends lengthily beyond the arc-shaped side of the fixing plate <NUM>. A pair of fastening holes <NUM> is formed through the pivoting plate <NUM> at positions corresponding to the pivot guide slit <NUM> of the fixing plate <NUM> such that the fastening holes <NUM> extend vertically through the pivoting plate <NUM>.

As shown in <FIG>, it may be possible to fix the pivoting plate <NUM> on the fixing plate <NUM> at a predetermined pivot position by fastening fasteners <NUM> constituted by bolts and nuts through the pair of fastening holes <NUM> of the pivoting plate <NUM> and the pivot guide slit <NUM> of the fixing plate <NUM>.

As shown in <FIG> and <FIG>, the pivoting plate <NUM> may be provided with a pair of movement guide slits <NUM> formed lengthily in a longitudinal direction. The pair of movement guide slits <NUM> may be formed through the pivoting plate <NUM> in parallel to have a predetermined length. A portion of the pivoting plate <NUM> overlapping with the moving plate <NUM> may have a reduced thickness and, as such, the pivoting plate <NUM> may be formed to have a step. In this case, the pair of movement guide slits <NUM> may be formed at the stepped thin portion of the pivoting plate <NUM>, and a limit position of the moving plate <NUM>, at which movement of the moving plate <NUM> toward the pivoting plate <NUM> is limited by the step, may be set.

The moving plate <NUM> may be provided with two pairs of fastening holes <NUM> formed through the moving plate <NUM> at positions corresponding to the pair of movement guide slits <NUM>. In the case in which an upper surface of the pivoting plate <NUM> at one side of the pivoting plate <NUM> is formed to be stepped, the moving plate <NUM> may also have a reduced thickness at one side thereof and, as such, a lower surface of the moving plate <NUM> at the side of the moving plate <NUM> may be formed to be stepped. The moving plate <NUM> may be formed to have a plate shape, and a cover may be coupled to the moving plate <NUM> in order to cover the bearing <NUM>, the driven pulley <NUM>, and the belt <NUM> mounted on the moving plate <NUM>. Alternatively, the plate and the cover are coupled to each other to be integrated and, as such, the moving plate <NUM> may be configured in the form of a case. In the latter case, a plurality of fastening holes <NUM> may be formed to extend through upper and lower surfaces of the moving plate <NUM> having the form of a case.

As shown in <FIG>, it may be possible to fix the moving plate <NUM> with respect to the pivoting plate <NUM> at a predetermined position in a longitudinal direction by fastening fasteners <NUM> through the plurality of fastening holes <NUM> of the moving plate <NUM> and the pair of movement guide slits <NUM> of the pivoting plate <NUM>. The fasteners <NUM> are constituted by bolts and nuts, and the two pairs of fastening holes <NUM> may be disposed outside the belt <NUM> in a width direction, in order to prevent the belt <NUM> from interfering with the bolts.

As shown in <FIG>, it is preferred that the moving plate <NUM> further include a tension roller <NUM> configured to adjust tension of the belt or chain <NUM> in such a manner that a rotation shaft of the tension roller <NUM> applies tension to the belt or chain <NUM> loosened in accordance with movement of the moving plate <NUM> in a state of being fixed after moving toward the belt or chain <NUM>. The following description will be given in conjunction with an example in which the belt <NUM> is used. Although the tension roller <NUM> is shown in <FIG> as being disposed at opposite outsides of the belt <NUM> in a width direction, it is more preferred that the tension roller <NUM> be disposed alone at one outside of the belt <NUM>. That is, only one tension roller <NUM> may be provided. In particular, although the tension roller <NUM> is shown in <FIG> as being disposed at the outsides of the belt <NUM> in the width direction in a lower region where the moving plate <NUM> is disposed, the tension roller <NUM> may be disposed at the outsides of the belt <NUM> in the width direction in an upper region where the fixing plate <NUM> is disposed. In addition, although not shown in <FIG>, a fixed roller may be provided at a right side of the movement guide slits <NUM> and an outside of the belt <NUM> in the width direction in the lower region when viewed in <FIG>, such that the belt <NUM> passes the fixed roller.

When the moving plate <NUM> is fastened in a state in which the moving plate <NUM> is disposed far from the pivoting plate <NUM>, as shown in <FIG>, the distance between the drive pulley <NUM> and the driven pulley <NUM> is increased. In this case, loosening of the belt <NUM>, which has a constant length, is relatively decreased.

On the other hand, when the moving plate <NUM> is fastened in a state in which the moving plate <NUM> is disposed nearer to the pivoting plate <NUM>, as shown in <FIG>, the distance between the drive pulley <NUM> and the driven pulley <NUM> is decreased. In this case, loosening of the belt <NUM>, which has a constant length, is relatively increased. To this end, the loosened belt <NUM> should be tensioned so that the belt <NUM> may transmit rotation force of the drive shaft <NUM> to the driven shaft <NUM>.

For this reason, the moving plate <NUM> may be provided with at least one tension roller <NUM> configured to push the belt <NUM> disposed over the moving plate <NUM> in a direction from an outside of the belt <NUM> to an inside of the belt <NUM> in the width direction. A pair of slits <NUM> extending in the width direction may be formed through the moving plate <NUM>, and rotation shafts <NUM> of tension rollers <NUM> may be firmly fastened to the slits <NUM> after being moved to appropriate positions in the slits <NUM>, respectively.

Although the belt <NUM> may be loosened in accordance with movement of the moving plate <NUM> with respect to the pivoting plate <NUM>, the belt <NUM> may be kept tensioned as the tension rollers <NUM> are fastened after being moved and, as such, rotation force may be smoothly transmitted.

Meanwhile, water supply hoses <NUM> may be connected to lower portions of the drive shaft <NUM> and the driven shaft <NUM>, respectively, to supply cooling water. That is, the two-hole core drilling machine <NUM> according to the exemplary embodiment of the present invention may be a wet core drilling machine configured to drill two holes by simultaneously rotating a plurality of core bits <NUM> while supplying water.

The water supply hoses <NUM> are detachably connected to a water supply pipe provided with a valve, and may be connected in parallel in order to supply water along channels communicating with interiors of respective core bits <NUM> after passing through interiors of the drive shaft <NUM> and the driven shaft <NUM>. Since the distance between the drive shaft <NUM> and the driven shaft <NUM> is variable, the water supply hoses <NUM> connected between the drive shaft <NUM> and the driven shaft <NUM> may be formed of a flexible material and may be connected while having a sufficient length.

In addition, the relative pivot angle between the two core bits and the distance between the two core bits may be adjusted and, as such, it may be possible to easily simultaneously drill two holes while appropriately adjusting the distance between the two holes to be drilled within a predetermined range.

<FIG> is a perspective view schematically showing an improved two-hole core drilling machine according to an exemplary embodiment of the present invention. <FIG> is a partial perspective view showing a structure configured to adjust the distance between two core bits and a rotation force transmission structure in the improved two-hole core drilling machine according to the exemplary embodiment of the present invention. <FIG> is a top view showing a pivot angle and length adjustment structure in the improved two-hole core drilling machine according to the exemplary embodiment of the present invention. <FIG> is a partial bottom perspective view corresponding to <FIG> in a state in which two core bits are omitted. <FIG> is a top view showing a state in which a moving plate is coupled to a fixing plate after moving with respect to the fixing plate from a state of <FIG>.

The two-hole core drilling machine according to the exemplary embodiment of the present invention, which is designated by reference numeral "<NUM>", includes a base <NUM> fixed to a structure to be drilled, a stand <NUM> vertically coupled to the base <NUM> and formed with a rack <NUM> at one side surface thereof, a vertically reciprocating carriage <NUM> provided with a pinion engaged with the rack <NUM> and vertically reciprocably mounted to the stand <NUM>, a motor <NUM> coupled to one side surface of the carriage <NUM>, a fixing plate <NUM> coupled to one side of a lower portion of the carriage <NUM>, to rotatably support a drive shaft <NUM> of the motor <NUM>, a pivoting plate <NUM> fastened to the fixing plate <NUM> under the condition that a pivot angle of the pivoting plate <NUM> is changed, and a moving plate <NUM> fastened to the pivoting plate <NUM> under the condition that a distance of the moving plate <NUM> from the fixing plate <NUM> is varied, and provided with a driven shaft <NUM> rotatably mounted thereto. The two-hole core drilling machine <NUM> also includes a drive force transmission (for example, a gear train) (in the following description, referred to as the "gear train" for convenience of description) <NUM> coupled between the drive shaft <NUM> and the driven shaft <NUM>, to transmit rotation force of the drive shaft <NUM> to the driven shaft <NUM>, a first core bit <NUM> coupled to the drive shaft <NUM>, and a second core bit <NUM> coupled to the driven shaft <NUM>.

The base <NUM> may be provided with at least one pair of anchor bolts <NUM> and, as such, may be fixed to a surface of a structure. In addition, the base <NUM> may be provided with at least one pair of wheels <NUM> and, as such, the entirety of the drilling machine <NUM> may be easily movable.

The carriage <NUM> may be provided therein with the pinion (not shown) engaged with the rack <NUM> and, as such, may be vertically reciprocably mounted to the stand <NUM>. The carriage <NUM> may be provided with a lever <NUM> configured to rotate the pinion. Accordingly, upon operating the drilling machine <NUM>, the operator may rotate the lever <NUM>, thereby vertically reciprocating the carriage <NUM>. In addition, guide grooves <NUM> may be formed at opposite side surfaces of the stand <NUM>, respectively, to guide and support vertical reciprocation of the carriage <NUM>.

The motor <NUM> may be coupled to an upper portion of one side surface of the carriage <NUM>, and the fixing plate <NUM> may be coupled to a lower portion of the side surface of the carriage <NUM>. The motor <NUM> may be an electric motor, and the drive shaft <NUM> thereof may be rotatably supported by a bearing (not shown) mounted to the fixing plate <NUM>.

The pivoting plate <NUM> may be mounted to a lower surface of the fixing plate <NUM> such that the pivoting plate <NUM> is pivotable about the drive shaft <NUM>. The pivoting plate <NUM> may be fixed to the fixing plate <NUM> by fasteners <NUM> under the condition that a pivot angle of the pivot plate <NUM> is changed.

In addition, the moving plate <NUM> may be firmly fastened to the pivoting plate <NUM> under the condition that a relative position of the moving plate <NUM> with respect to the pivoting plate <NUM> is varied, in order to vary a distance between the moving plate <NUM> and the fixing plate <NUM>. The driven shaft <NUM> may be rotatably mounted at a through hole formed at a center of the moving plate <NUM>.

The gear train <NUM> is coupled between the drive shaft <NUM> and the driven shaft <NUM>, to transmit rotation force of the drive shaft <NUM> to the driven shaft <NUM>. The gear train <NUM> may be constituted by two link brackets and five gears. A concrete configuration of the gear train <NUM> will be described later. A drive gear <NUM> may be coupled to the drive shaft <NUM>, and a driven gear <NUM> may be coupled to the driven shaft <NUM>, and, as such, the motor <NUM> may simultaneously rotate the drive shaft <NUM> and the driven shaft <NUM>. As shown in <FIG>, the driven shaft <NUM> may be disposed to pass through a shaft hole <NUM> formed through a central portion of the pivoting plate <NUM> at one side of the pivoting plate <NUM> in the form of a large slot.

The first core bit <NUM> is coupled to a lower end of the drive shaft <NUM>, and the second core bit <NUM> is coupled to a lower end of the driven shaft <NUM>. The first core bit <NUM> and the second core bit <NUM> may have the same size. However, two core bits having various sizes may be coupled to the drive shaft <NUM> and the driven shaft <NUM>, respectively.

In the two-hole core drilling machine <NUM> according to the exemplary embodiment of the present invention, the first core bit <NUM> and the second core bit <NUM> may be fixed in a state in which pivot angle positions of the first core bit <NUM> and the second core bit <NUM> with respect to the base <NUM> and a relative distance between the first core bit <NUM> and the second core bit <NUM> are adjusted. Thus, the two-hole core drilling machine <NUM> may simultaneously drill two holes in a state in which a relative pivot angle and a relative distance between the two holes is appropriately adjusted.

The fixing plate <NUM> may be formed to take the form of a rectangular plate having an arc shape at one side thereof. Linear sides of the fixing plate <NUM> may be coupled to the carriage <NUM> and, as such, the fixing plate <NUM> may be vertically reciprocable together with the carriage <NUM>. The fixing plate <NUM> may be provided with a plurality of fastening holes arranged on a circumference having a predetermined radius from the drive shaft <NUM>.

The pivoting plate <NUM> may be provided with a plurality of fastening holes <NUM> extending vertically through the pivoting plate <NUM>. The plurality of fastening holes <NUM> of the pivoting plate <NUM> may be formed at positions corresponding to the plurality of fastening holes of the fixing plate <NUM>, respectively. The pivoting plate <NUM> may be formed to take the form of a rectangular plate having an arc shape at both shorter sides thereof.

The moving plate <NUM> may be formed to take the form of a substantially-square plate chamfered at four corners thereof. A guide groove <NUM> may be formed in a longitudinal direction at an upper surface of the pivoting plate <NUM>, to guide movement of the moving plate <NUM> seated therein.

A protrusion (not shown) may be formed at one side of a lower surface of the moving plate <NUM> contacting the guide groove <NUM>. A groove (not shown), which engages with the protrusion, thereby allowing stable movement of the moving plate <NUM> while preventing separation of the moving plate <NUM>, may be formed at the pivoting plate <NUM>.

It may be possible to fix the pivoting plate <NUM> at a predetermined pivot position with respect to the fixing plate <NUM> by fastening the fasteners <NUM> through the plurality of fastening holes of the fixing plate <NUM> and the plurality of fastening holes <NUM> of the pivoting plate <NUM>. In the case in which eight fastening holes <NUM> are formed at the pivoting plate <NUM>, as shown in <FIG>, it may be possible to firmly fasten fasteners <NUM> at positions where the pivoting plate <NUM> is pivoted with respect to the fixing plate <NUM> through <NUM>°, respectively.

As shown in <FIG>, the pivoting plate <NUM> may be provided with a plurality of slits <NUM> formed lengthily in a longitudinal direction, and the moving plate <NUM> may be provided with a plurality of fastening holes <NUM> extending vertically through the moving plate <NUM>. In the shown embodiment, three pairs of slits <NUM> may be formed at the pivoting plate <NUM>, and three pairs of fastening holes <NUM> may be formed at the moving plate <NUM>.

As shown in <FIG>, the gear train <NUM> may include a first link bracket <NUM> pivotably mounted to the drive shaft <NUM>, a second link bracket <NUM> pivotably connected, at one end thereof, to the first link bracket <NUM> while being pivotably mounted, at the other end thereof, to the driven shaft <NUM>, the drive gear <NUM> coupled to the drive shaft <NUM>, to be rotatable by the drive shaft <NUM>, a first intermediate gear <NUM> mounted to the first link bracket <NUM> while engaging with the drive gear <NUM>, a second intermediate gear <NUM> mounted to connection portions of the first link bracket <NUM> and the second link bracket <NUM> while engaging with the first intermediate gear <NUM>, a third intermediate gear <NUM> mounted to the second link bracket <NUM> while engaging with the second intermediate gear <NUM>, and the driven gear <NUM> coupled to the driven shaft <NUM> while engaging with the third intermediate gear <NUM>, to be rotatable by the third intermediate gear <NUM>.

The first link bracket <NUM> may be disposed over and under three gears, and rotation shafts of the three gears may be mounted to the first link bracket <NUM>. The first link bracket <NUM> may be formed to take the form of a pair of rectangular plates each having a semicircular shape at both shorter sides thereof. One side of the first link bracket <NUM> may be pivotably mounted to the drive shaft <NUM>.

The second link bracket <NUM> may also be formed to take the form of a pair of rectangular plates each having a semicircular shape at both shorter sides thereof. Rotation shafts of three gears may be mounted between the pair of second link brackets <NUM>. Other-side portions of the pair of first link brackets <NUM> and one-side portions of the pair of second link brackets <NUM> may be formed to have a thickness reduced by half, thereby forming steps, respectively, and, as such, may be interconnected to be pivotable with respect to each other about a rotation shaft of the second intermediate gear <NUM>.

The drive gear <NUM> may be coupled to the drive shaft <NUM> rotated by the motor <NUM> and, as such, may rotate together with the drive shaft <NUM>.

The first intermediate gear <NUM> may be rotatably mounted between middle portions of the pair of first link brackets <NUM>, and may engage with the drive gear <NUM> and, as such, may be rotated.

The second intermediate gear <NUM> may be mounted between the connection portions of the first link bracket <NUM> and the second link bracket <NUM>, and may engage with the first intermediate gear <NUM> and, as such, may be rotated.

The third intermediate gear <NUM> may be mounted between the middle portions of the pair of second link brackets <NUM>, and may engage with the second intermediate gear <NUM> and, as such, may be rotated.

The driven gear <NUM> may be coupled to the driven shaft <NUM> mounted to the other-side portions of the pair of second link brackets <NUM>, and may engage with the third intermediate gear <NUM> and, as such, may be rotated.

As shown in <FIG>, it may be possible to fix the moving plate <NUM> by slightly unfastening the fasteners <NUM> fastened to the slits <NUM> of the moving plate <NUM> and the fastening holes <NUM> of the moving plate <NUM>, moving the moving plate <NUM> rightwards, and then again fastening the fasteners <NUM>. In this case, the moving plate <NUM> may be fixed at a position farther from the fixing plate <NUM>, as compared to the case of <FIG>. In this case, the angle between the first link bracket <NUM> and the second link bracket <NUM> may be fixed in a slightly diverged state.

Meanwhile, as shown in <FIG>, water supply hoses <NUM> may be connected to a side surface of a middle portion of the drive shaft <NUM> and a side surface of an upper portion of the driven shaft <NUM>, respectively, to supply cooling water. That is, the core drilling machine <NUM> according to the exemplary embodiment of the present invention may be a wet core drilling machine configured to drill holes by simultaneously rotating core bits while supplying water.

Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope of the invention as disclosed in the accompanying claims.

Claim 1:
A two-hole core drilling machine (<NUM>) comprising:
a body;
a vertically reciprocating carriage (<NUM>) vertically reciprocably mounted to the body;
a fixing plate (<NUM>) coupled to one side surface of the carriage (<NUM>), to rotatably support a drive shaft (<NUM>) of a motor (<NUM>);
the two-hole core drilling machine (<NUM>) being characterized by comprising:
a pivoting plate (<NUM>) fastened to the fixing plate (<NUM>), a pivot angle of the pivoting plate (<NUM>) is changeable;
a moving plate (<NUM>) fastened to the pivoting plate (<NUM>), a length of the moving plate (<NUM>) from the pivoting plate (<NUM>) is variable;
a belt or chain (<NUM>) mounted between a drive pulley (<NUM>) coupled to the drive shaft and a driven pulley (<NUM>) coupled to a driven shaft (<NUM>) rotatably mounted to the moving plate (<NUM>);
a first core bit (<NUM>) coupled to the drive shaft (<NUM>); and
a second core bit (<NUM>) coupled to the driven shaft (<NUM>).