Magnetic based drill assemblies (magdrills) are used extensively in the metal fabricating field for forming holes in various workpieces where it is either impractical or inconvenient to move the workpiece to a conventional drill press. Accordingly, as the magdrill is moved to the workpiece, it is advantageous to provide the most portable and compact drill assembly possible. Additionally, as the drill assembly is operated in a construction environment it is preferable that the magdrill have a minimum number of exposed moving parts. The minimization of exposed parts not only decreases the likelihood of injury to an operator, but also improves the durability and the maintenance requirements of the magdrill.

Typically, magnetic based drill assemblies have an arbor coupled to a motor which is attached to a slide assembly. The slide assembly is mounted for vertical movement in relation to a magnetic base. A handle is typically used to rotate a gear which rectilinearly moves the slide assembly between a retracted position and an extended position to form a hole in a workpiece. Thus, to drill a hole, the entire motor, arbor, slide, and drill tool must be slidably actuated in a vertical plane relative to the magnetic base.

Drilling a precision hole in a substantial workpiece such as a steel I-beam, pipe or plate, requires a relatively powerful electrical motor an acceptable rate of operation. Due to the strength and precision required to moveably support the entire motor, arbor, slide, and drill tool, the drill assembly is relatively bulky and difficult to maneuver along a workpiece. Additionally, the quantity, weight and height of the moving parts provide an unbalanced drill assembly having a center of gravity which changes as the moving parts are vertically manipulated during drilling operations.

The multiple moving parts, bulkiness, and unbalanced nature of conventional magdrill assemblies thus increase the danger to an operator and increase the amount of maintenance required to keep the drill assembly operational.

Further, it is preferable to introduce a liquid coolant to the drill tool and workpiece during operation of the drill assembly to reduce friction and heat. The liquid coolant is commonly provided from a storage tank to the drill tool by gravity or pressure. To introduce coolant to a drill tool through typical arbors commonly requires a series of intricately formed passageways or the installation of an adaptor adjacent the drill tool. However, in addition to the complexity of either method, the coolant is not fed directly into the drill tool which thereby reduces coolant and drill tool effectiveness.

Thus, there is a need for a magnetic based drill which is compact, has a minimum number of exposed moving parts and is of a relatively light weight.

SUMMARY OF THE INVENTION The present invention provides a magnetic based drill assembly comprising a support platform mounted to the magnetic base for attachment to a work piece. A support housing is mounted to the platform for supporting a motor in a stationary position. A gear train operatively interconnects the motor and a splined arbor. A feed mechanism is operatively connected to the platform for rectilinear movement between a fully retracted position and a fully extended position. The feed mechanism includes a splined collar slidably mounted to the splined arbor for movement relative to the splined arbor and for rotatably supporting a drive tool.

Having mounted the motor in a stationary position off the slide, the subject invention reduces the strength and precision requirements of the slide. In addition, by placing the motor in a stationary position on the support housing opposite the arbor, the overall package size of the present invention is relatively compact compared

to typical magnetic based drill assemblies as the motor does not move vertically with the drill tool during operation.

Moreover, as the splined arbor is located within a cylindrical feed arbor a liquid coolant can be directly injected into the drill tool during operation of the drill assembly. Preferably, a through bore is located in the splined arbor to direct coolant from a storage tank directly into the drill tool. Further, as the splined arbor and feed arbor are solid the coolant can be directed under pressure thus allowing drilling operation to take place out of the horizontal plane while maintaining drill tool effectiveness.

Accordingly, the present invention provides a magnetic based drill assembly which is compact, has a minimum number of exposed moving parts, is of a relatively light weight, has a relatively stationary center of gravity and integrates pressurized coolant allowing overhead drilling operations.

BRIEF DESCRIPTION OF THE DRAWINGS The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows: Figure 1 is a perspective view of the present invention Figure 2 is a sectional view from the opposite side of the present invention shown in figure 1; Figure 3 is an exploded view of the feed mechanism assembly of the present invention; Figure 4 is a side view of the of the feed mechanism assembly of figure 3 shown between the fully retracted and extended positions; and Figure 5 is an exploded view of a feed sensing device of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Figure 1 illustrates a magnetic based drill assembly 10 according to the present invention. For purposes of clarity, the present invention will be described with respect to a magnetic based drill with it being understood that pneumatic bases, couplings, etc. could be used.

As shown in Figures 1 and 2, the magdrill assembly 10 includes a support platform 12 mounted to a magnetic base 14. A support housing 16, presenting a front end 18 and a rear end 20 opposite the front end 18, is mounted to the support platform 12. A motor 22, presenting a drive axis A,, is mounted to the support housing 16 adjacent to the rear end 20 of the support housing 16. A 180° gear train 17, of a type known in the art, is disposed in the support housing 16 and is operatively connected to the motor 22. A splined arbor 24, presenting a driven axis A2, is rotatably supported by the gear train 17 for rotation about the driven axis A2.

A feed mechanism, generally indicated at 26, is slidably connected to the splined arbor 24.

With reference to figures 3 and 4, the feed mechanism 26 includes a splined arbor collar 28 which operatively mates with the splined arbor 24 along splines 25. The arbor collar 28 has a stepped portion 32 which is received within the head 33 of the hollow feed arbor 34. The head 33 has a recess 35 for receipt of stepped portion 32. A set screw 37 or the like can be used to connect the collar 28 to the head 33.

The head 33 includes a stepped portion 39 which is received within a bearing 42 which allows the collar 28 to rotate with respect to the support bracket 38. The feed arbor is press fit into bearing 42. The splined arbor 24 is telescoped into the hollow feed arbor 34 so that the feed arbor 34 can be moved rectilinearly with respect to the splined arbor 24.

The feed mechanism 24 further includes a slide 36 slidably supported by the support platform 12 for movement between fully retracted and fully extended positions along arrow 15. The slide 36 is dove-tailed into the support platform and includes a

reduced friction material therebetween. Preferably, adjustable brass gibbs 11 and multiple set screws 17 (figure 1) allow friction and wear between the slide 36 and the support platform 12 to be regulated Movement of the slide 36 is controlled in a manner known in the art and includes a rack 60 and pinion 62 arrangement (figure 2). The rack 60 is attached to slide 36 and the pinion 62 is attached to a handle 64. By rotating the handle 64, the pinion 62 rotates and moves the rack 60 and slide 36 up and down in the direction of arrow 15. The present invention further provides for the pinion axil 66 to pass through the support platform 12 allowing the handle 64 to be removably affixed to either side. The same handle 64, rack 60, and pinon 62 arrangement thus provide for both left or right hand operation. Additionally, by replacing pinion 62 with an alternate gear assembly the rotation of handle 64 to slide 36 movement can be controlled.

A support bracket 38 is fastened to the slide 36. The support bracket 38 includes an aperture 40 at the distal end of the support bracket 38. Bearing 42 is rotatably retained in the aperture 40 of the support bracket 38. The feed arbor 34 is press fit in the bearing 42, whereby the feed arbor 34 is moved between the fully retracted and extended positions while being free to rotate.

The assembly 10 further includes a guide bracket 44 mounted to the magnetic base 14 for guiding the feed arbor 34. The guide bracket 44 includes a guide collar 46 at the distal end of the guide bracket 44. An annular bearing ring 48 is rotatably retains the feed arbor 34 in the guide collar 46. Although a bearing ring 48 is preferred, it will be recognized that a metallic or composite bushing could also be installed.

The feed arbor 34 is slidably disposed in the annual bearing ring 48, wherein a pin 50 is disposed in a slot opening 52 extending lengthwise in the feed arbor 34.

The bearing ring 48 allows the feed arbor 34 to rotate and move rectilinear while pin 50 controls the vertical limits of feed arbor 34.

To inject a liquid coolant directly to the drill tool a quick attach coupling 27 is provided on support housing 16 (figure 2). The coupling 27 feeds coolant into a bore 29 drilled centrally along the length of splined arbor 24. By injecting coolant by gravity or under pressure from a coolant tank (not shown) attached to coupling 27 through bore 29 the coolant is directed directly to the drill tool 68. Further, the solid cylindrical configuration of feed bore.

The feed arbor 34 further includes a positive slug ejection assembly 74. To drill a hole with the present invention the drill tool 68 is preferably a rotorbroach tool which creates a slug of material during the drilling operation. This slug of material is commonly retained within the tool 68 and must be removed prior to the next drilling operation. To remove the slug a spring 76 forces an ejector pilot 78 through the hollow rotorbroach tool to positively eject the slug. On some occasions the spring 76 is insufficient to eject the slug. The present invention thus provides for the feed arbor 34 to be retracted in the normal manner to allow the splined arbor 24 to contact the ejector pilot 78 and forcibly expel the slug from the rotorbroach. By this method the slug is easily and quickly removed without delaying the drilling operation.

In operation, the motor 22 rotates about the drive axis A, driving the gear train. In turn, the gear train rotates the splined arbor 24 about the driven axis A2.

At the same time, the collar 28 forces the feed arbor 34 to rotate, which causes the drill tool 68 to rotate.

As described hereinabove, the movement of the slide 36 between the fully retracted and extended positions is controlled by a pinion 62 and rack 60 in a manner known in the art. As the slide 36 moves, the feed arbor 34 moves relative to the splined arbor 24 and guide bracket 44. The splined arbor 24 telescopes into and out of the hollow feed arbor 34. To protect the few exposed rotating parts, a plastic bellows 70 (figure 1), cover 72 (figure 2), or the like, can be placed over the splined arbor 24 or the entire frontal portion 18 of assembly 10.

As shown in Figure 5, to control the drill tool 68, the assembly 10 includes an electrical feed rate monitor 80 for providing a signal to the user as to the optimal

feed rate of the drill tool 68. The monitor includes a red 82, a green 84 and a yellow 86 Light Emitting Diode. The LED's are selectively triggered by the amount of current drawn by the motor 22. For example only, if an inadequate amount of pressure is applied, the yellow LED 86 is triggered to signal the user to increase the feed rate. The green LED 84 signals the user to maintain the current feed rate and if to much pressure is applied the red LED 82 indicates that the feed rate should be decreased.

Furthermore, the assembly includes a sensing device 88 (figures 1 and 2) for disconnecting the power to the motor 22 when the movement of the magnetic base 14 causes an acceleration in excess of a specified limit. The sensing device preferably includes an accelerometer mounted to the magnetic base 14. In the event the torque transmitted by the drill tool 68 causes the magnetic base 14 to move, the accelerometer provides an input signal to a signal conditioner. In turn, the signal conditioner outputs an amplified signal to a circuit board. Provided the amplified signal exceeds a specified value corresponding to the acceleration limit, the circuit board provides a signal activating a switch disconnecting the power to the motor 22.

The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, wherein reference numerals are merely for convenience and are not to be in any way limiting, the invention may be practiced otherwise than as specifically described.