Abstract:
The present invention discloses a torque restraining device to resist the lateral shifting or rotation of a self adhering drill unit due to the torque generated by the drill motor. The torque restraining device includes a penetrating member mounted on the bottom of the drill unit for penetrating the work surface to prevent rotation of the drill unit during use. The penetrating member is embedded by the action of the drill unit being pulled to the work surface when the mounting base of the drill unit is activated. In the preferred embodiments, a protective sleeve is reciprocally mounted about the penetrating member to encase the penetrating member to prevent damage when the base is not activated. Upon activating the base, the sleeve retracts to expose the penetrating member for penetration into the work surface. The protective sleeve or glide post protects the conical end of the penetrating member and when the base is not activated lifts the rear of the drill unit from the work surface to disengage the penetration member and to facilitate easy sliding of the drill unit. In a further embodiment of the invention, a driving means is included to facilitate penetration.

Description:
BACKGROUND OF INVENTION 
     The present invention relates to portable drill units that are provided with a magnetic base, suction cup or other device to attach the drill unit to a work surface. More particularly, the present invention relates to a torque restraining device for resisting movement of the drill unit during operation. For clarity, the invention will be described with respect to a drill unit having an electromagnetic base. However, it should be understood that the electromagnet could be replaced by suction cups or equivalent means to make the portable drill unit self attaching. 
     Basically, a magnetic base drill is a portable drill press. It includes an electromagnet, a support affixed to the electromagnet and an electric drill motor reciprocally mounted to the support member so that it can be raised and lowered with respect to the work surface. The electromagnet is energized to create a magnetic flux between the electromagnet and the work surface to magnetically adhere the magnetic base drill to the work surface. In this way, holes may be drilled in a work surface at remote locations where a standard drill press could not be taken. Common uses for magnetic base drills are in the construction and repair of bridges, high-rise buildings, etc. 
     The torque of a magnetic base drill causes a twisting or torsional force which must be resisted by the magnetic base of the drill. The motor of the magnetic base drill produces high torques when loaded down, tremendous torques when bogged down and even greater torques when the motor is stalled. The highest torque, the torque obtained when the motor is stalled, is called the stall torque and occurs when the rotation of the motor is stopped or stalled in the work. This stall torque is significantly higher than normal operating torques of the motor. Unless the magnet of the magnetic base drill resists all of these torques, the magnetic base drill may slip or even break away from the work surface and spin out of control. 
     The electromagnet of a magnetic base drill creates a strong normal force to attract the drill to the work surface, but consderably less force to resis rotation. With standard magnetic base drills, not including a torque restraining device, the electromagnet cannot adequately resist this twisting rotation resulting in inadvertent movement. 
     An early attempt at solving the problem of inadvertent rotation of magnetic base drills is disclosed in U.S. Pat. No. 2,622,457 to Buck. Buck attempted to solve the problem by using two magnets spaced from one another. The difficulty with this attempt is the fact that magnets have very little resistance to torsional movement. Even though one of the magnets is spaced a distance from the other, the resistance to torsional movement is not greatly enhanced. 
     United States Patent No. 4,261,673, issued to Everett D. Hougen discloses a solution to the problem of inadvertent rotational movement. The solution involves the driving of a torque restraining device into the work surface to prevent rotational movement. It was discovered by Mr. Hougen that the amount of penetration needed to resist rotation is relatively small, even though the stall torque of the motor was very great. Mr. Hougen discovered a synergistic effect between a torque restraining pin that penetrates the work surface and the magnetic attraction of an electromagnet. Neither the magnet nor the torque pin when used separately provided enough resisting torque. When used together, the resistance torque was greater than the sum of the torque resistance provided by the pin and magnet and was found to be enough to prevent rotation and resist the stall torque of the motor. With a slight penetration of the pin and the force of the electromagnet, the resistance to rotation is dramatically increased over the available resistance from the electromagnet alone. As disclosed in the &#39;673 patent, there are several different ways to drive the torque restraining device into the surface. 
     In addition to the torque restraining pin, the &#39;673 patent discloses the use of a roller to permit the magnetic base drill to be easily aligned over the place where a hole is to be drilled. (This roller is also disclosed in U.S. Pat. No. 3,969,036.) Many times, holes must be drilled at exact predetermined locations and alignment is crucial. By using the roller, the drill can be easily slid across the work surface to each location and aligned. Further, the ability to slide the magnetic base drill across the work surface clears away metal chips which have been left on the surface during drilling. The front of the magnetic base drill with the rear raised by the roller acts as a scraper to clear the work surface of metal chips to provide a better surface for the magnet to adhere. 
     A disadvantage of the torque restraining device of the &#39;673 patent is the exposed torque restraining pin. If the magnetic base drill is handled roughtly, there is the possibility that the torque restraining pin may be dulled. The penetration of the torque restraining pin may be only about 0.015 inches, and therefore a dull or chipped pin may be insufficient to restrain the torque generated. Commonly, the operator&#39;s manuals for drill presses of this type advise the operator to maintain the sharpness of the pin. 
     A further disadvantage of the &#39;673 patent is the use of a separate torque restraining device and plunger. This requires a larger mounting area which increases the size, weight and manufacturing cost of the magnetic base drill. Still further, positioning the torque restraining device and/or plunger of the magnetic base drill center line can be disadvantageous in some applications. By combining the torque pin and glide or protective member into one unit both can be located where they are most effective, for example, along the center line of the magnet when used on tubing. 
     BRIEF SUMMARY OF THE INVENTION 
     The present invention overcomes the disadvantage of an exposed torque pin as found in the &#39;673 Hougen patent and provides the additional benefit of a single torque restraining member which provides restraint against rotational movement and a glide member for moving the unit. This eliminates the need for a separate glide roller and torque restraining device. 
     The torque restraining device of the present invention has a penetrating member or torque pin mounted on the bottom of the magnetic base drill for penetrating the work surface to prevent rotation of the magnetic base drill during use. A protective member is reciprocally mounted about the torque pin and axially moves with respect to the torque pin. The protective member is retractable to expose the penetrating member for penetration into the work surface. 
     When the magnet is not energized, the protective member encases the torque pin to prevent damage to the end of the pin. When the magnet is energized, the protective member retracts to expose the torque pin. 
     Preferably, the penetrating member is fixed to protrude beyond the bottom of the magnetic base drill for penetration into the work surface. Preferably, the protective member is a sleeve which is biased by a spring or equivalent biasing means to protrude beyond the bottom of the magnetic base and the penetrating member. The bias of the spring against the protective sleeve lifts the magnetic base drill with respect to the work surface when the magnet is not energized. Further, in the preferred embodiment, the end of the protective sleeve is rounded so that the magnetic base drill can be more easily slid upon the work surface so that it functions in a manner similar to the roller of the &#39;673 Hougen patent. 
     In the most preferred embodiment, the torque restraining device includes a bracket which can be easily mounted to the rear of a magnetic base drill, spacing the torque restraining device as far as practical from the drill but or cutting tool axis to provide maximum torque resistance. This bracket has a bore extending through it. The bore has two portions; a first portion which extends from the top partially through the mounting bracket and ends in a second portion. The second portion extends from the first portion through the bottom of the mounting bracket. The second portion has a smaller diameter than the first portion which creates a support ledge at the adjoining ends of the first and second portions. The protective sleeve includes a flange which is configured to rest upon this supporting ledge. In this way, the protective sleeve is retained within the bore and is free to reciprocate within the bore. 
     In the preferred embodiment, the torque pin includes an upper head portion and a depending shaft with an end for penetrating the work surface, such as a pointed or conical end. The shaft is received within the bore of the protective sleeve so that the protective sleeve can reciprocate with respect to the torque pin. The spring is mounted to bias against the upper portion of the torque pin. 
     In a further embodiment of the present invention, a driving means is provided to facilitate the penetration of the torque pin. In one embodiment, the torque pin is machined from a larger diameter rod which is threaded into the mounting bracket so that the machined penetrating pin extends below the bottom of the mounting bracket. In this embodiment, the magnet draws the pin into the work surface, and the rod is adapted to be driven or impacted to further penetrate the pin. A locking nut is threaded onto the rod to help absorb the impact. In another embodiment, a slide hammer can be mounted to the opposite end of the machined rod above the mounting bracket or above the head portion of the torque pin previously discussed. The protective sleeve is similar to the protective sleeve of the preferred embodiment in that it reciprocates with respect to the penetrating pin. When the magnetic base drill is energized the penetrating pin is pulled into the surface and then to assure full penetration or if greater penetration is desired the slide hammer can be raised and lowered rapidly against a locking nut ont he shaft or the mounting bracket to drive the torque pin further into the surface. 
     In a still further embodiment of the present invention, the protective member is a coil spring which is mounted about the torque pin. The spring is preferably mounted with a bore which opens from the bottom of the magnetic base drill. However, a bore is not necessary as the spring could be mounted to the base of the magnetic base drill, if for example, the base of the drill is offset vertically to provide clearance for the spring when retracted or compressed. The spring has sufficient bias to raise the magnetic base with respect to the work surface when the magnet is de-energized and will permit the drill to be more easily slid along the work surface similar to the protective sleeve of the preferred embodiment. 
     Other advantages and meritorious features of the present invention will be more fully understood from the following description of the invention, the appended claims, and the drawings, a brief description of which follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a perspective view of a magnetic base drill with the torque restraining device of the present invention shown in an exploded view. 
     FIG. 2 is a partial side view of a magnetic base drill employing the torque restraining device of the present invention. 
     FIG. 3 is a partial cut away view of the torque restraining device of the present invention penetrated into the work surface. 
     FIG. 4 is a cut away view of the torque restraining device of the present invention which is similar to the preferred embodiment except that a driving means is added to facilitate penetration of the torque pin. 
     FIG. 5 is a cross-sectional view of a further embodiment of the present invention. 
     FIG. 6 is a cross-sectional view of a still further embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     With reference to FIG. 1, the torque restraining device of the present invention is shown generally at 10 mounted within a rear support bracket 12 which is fixed to the rear of a magnetic base drill 14. Rear mounting bracket 12 may be integrally formed with the magnet portion 15 of drill 14 of it may be affixed by bolts or other conventional connecting means. 
     Bracket 12 includes a bore 16 extending through the top to the bottom of bracket 12. This bore has first and second communicating portions 18 and 20 respectively. Portion 18 extends partially through bracket 12 and ends in second portion 20 which extends the remaining distance of bracket 12. The inner diameter of the first portion 18 is greater than the inner diameter of the second portion 20 forming a support ledge 22 at the adjoining ends of the first and second portions 18 and 20 respectively. 
     Torque restraining device 10 is mounted within longitudinal bore 16. Device 10 includes a glide post or protective sleeve 24 which has a tubular body portion 26 and a flange 28. Flange 28 has an outer diameter which is slightly less than the inner diameter of the first portion 18 of bore 16. The outer diameter of tubular body portion 26 is slightly less than the inner diameter of second portion 20. Glide post 24 normally rests upon support ledge 22 but is free to reciprocate within bore 16. With reference to FIG. 2 it can be seen that when glide post 24 is resting upon support ledge 22, tubular body portion 26 protrudes below the bottom of bracket 12. 
     Mounted within bore 30 of glide post 24 is torque reactor 32. Preferably, reactor 32 has an upper, top or head portion 34 and a body portion 36 having an end which is configured to penetrate the work surface, such as for example a conical end or point 38. Mounted between head portion 34 and flange 28 of glide post 24 is a biasing means 40 to normally bias the torque reactor point 32 and glide post 24 in opposite directions. In the disclosed embodiment, biasing means 40 is a coil spring which has sufficient resiliency to force glide post 24 against support ledge 22 and raise the magnetic base drill 14 with respect to the work surface as shown in FIG. 2. 
     A locking plug 42 is mounted in the top internally threaded portion of bore 16 to retain the spring biased members within bracket 12 and to adjust the protrusion of reactor point 32 beyond the base of the drill. In the preferred embodiment, the upper portion of bore 16 is counter sunk at 44 and has internal threads 46 for receipt of threads 47 of plug 42. A lock nut 51 is threaded onto threads 47. Alternatively, plug 42 and head portion 34 could be integrally formed with plug 42, forming the head of reactor 32 with body portion 36 depending therefrom. 
     With reference to FIG. 2, the glide post 24 is shown in its normal position wherein it raises the rear of magnetic base drill 14 with respect to the work surface 49. The free end of the glide post 24 is preferably rounded at 48 so that the magnetic base drill 14 can be freely moved with respect to work surface 49. In this way, the end 38 of torque reactor point 32 is protected from abuse and the magnetic base drill 14 can be easily moved with respect to surface 49. An additional benefit is the contact of the front 50 of magnetic base drill 14 with work surface 49. The front 50 acts as a scraper to clear away any debris on the work surface which may interfere with the magnet 15 adhering to the work surface. Since magnetic base drills of this type are used on metal surfaces, large amounts of oil are needed to reduce heat in the cutting operation and metal chips result from the cutting operation. The chips and oil litter the work surface and interfere with the magnet 15. The combination of glide post 24 lifting the rear of the magnetic base drill 14 and the contact of the front 50 with the work surface scrapes the work surface as the drill is moved to provide a clean surface for electromagnet 15. 
     Once the magnetic base drill 14 is properly aligned for cutting a hole, the electromagnet 15 is energized which pulls the electromagnet 15 flush with the work surface 49 and simultaneously drives the end 38 of reactor 32 into the work surface. As the magnetic base drilll 14 is pulled to the surface, glide post 24 retracts within bracket 12 compressing spring 40 against head portion 34. Post 24 is retracted to expose the end 38 of reactor 32. The compression of spring 40 and its action against head portion 34 results in torque reactor point 32 being substantially rigid with bracket 12 facilitating penetration of end 38. 
     With reference to FIG. 3, point 38 is shown penetrating work surface 49. As can be seen, the penetration of point 38 creates bulges 52 in the work surface which are squeezed into the bore 30 of glide post 24. This bulge of material 52 protruding into the bore 30 of glide post 24 enhances the resistance of the unit to rotation or skidding about the cutting tool of the magnetic base drill. 
     Upon de-energizing the magnetic base drill, spring 40 biases glide post 24 in the direction of the work surface to raise the rear of magnetic base drill 14. This pulls conical point 38 out of the work surface releasing the magnetic base drill 14 for movement along the work surface. Once released, the magnetic base drill 14 may be pushed across the work surface to clean a path for the electromagnet 15 and to locate the cutting tool (not shown) to cut another hole. 
     With reference to FIG. 4, a further embodiment of the present invention is illustrated. In this embodiment, the restraining member is again shown generally at 10 with similar elements having identical numbering. In this embodiment, a penetration enhancer has been added to the torque restraining device. In some applications, it may be necessary to add an enhancing means to ensure proper penetration of end 38 for proper resistance. In this embodiment, instead of using plug 42, driving member 80 has been added. Member 80 includes a rod 82 which has a threaded end 84 that is threaded into the threaded opening 46 of bore 16. A slide hammer 86 is mounted over rod 82. Hammer 86 can be raised and then lowered rapidly to further drive end 38 into the work surface after the magnet is energized. The slide hammer 86 includes a bore 88 which is received over a guide portion 90 and fixed to rod 82 by a locking cap and screw 92. 
     The location of impactor 80 as illustrated in FIG. 4 is not critical. As will be understood, however, the torque restraining device should be spaced as far as practical from the drill bit or cutting tool to obtain the maximum mechanical advantage, preferably at the rearward portion of the magnet 15. Additionally, the alignment of torque restraining device 10 is not critical. It is shown positioned along the longitudinal center line of magnetic base drill 14 which is the preferred position; however, other locations of the impactor are within the scope of this invention because location on the center line is not critical. 
     With reference to FIG. 5, a further embodiment of the present invention is illustrated. In this embodiment, the torque restraining device is generally shown at 60. Elements which are similar to those previously discussed have the same number. The torque reactor point 32 of the present embodiment is formed by machining a cylindrical rod 62 to form the body portion 36 and end 38 of the reactor point 32. Just above the torque restraining point 32, rod 62 is threaded at 64 to form the head of reactor point 32 for receipt in the threaded opening 46 of bore 16. The glide post 24 is identical to the previous glide post and has a tubular body 26 and flange 28 which rests upon a support ledge 22. In this embodiment, the top 68 of rod 62 may be hit downwardly to further penetrate end 38 into a work surface after the electromagnet is energized. 
     In operation, the embodiment of FIG. 5 works substantially the same as the previous embodiments. Upon energizing the electromagnet 15 of the magnetic base drill 14, the glide post 24 is retracted within bore 16 against the bias of spring 40. This retraction exposes end 38 and due to the force of the electromagnet being pulled to the work surface and, if desired, the force applied to rod 62, end 38 is driven into the work surface. To ensure proper penetration of end 38, force may be applied to rod 62 to further drive the end 38 into the surface. This is helpful when drilling into a hard surface for example. If a deeper penetration is desired, rod 62 can be screwed into threaded opening 64 to lengthen the protrusion of end 38 past the bottom of the electromagnet 15 of magnetic base drill 14. Alternatively, rod 62 can be backed out of opening 64 to shorten the protrusion. 
     With reference to FIG. 6, a still further embodiment of the present invention is illustrated. In this embodiment, the glide post 24 of the previous embodiments is replaced with coil spring 108 which performs the function of glide post 24. In this embodiment, the torque reactor point 32 has a body portion 36 ending in a conical end 38 with an externally threaded head portion 100 at the opposite end. A lock nut 102 is threaded onto head portion 100. It should be understood that the torque restraining device 32 illustrated in FIG. 6 could be replaced by any of the previously described torque restraining devices or any equivalent devices which resist torque. 
     The torque restraining device 32 of FIG. 6 is mounted within a bore 104. A coil spring 108 is mounted around body portion 36 within bore 104. Preferably, spring 108 is held within bore 104 by a set screw 110 which is received with a small internally threaded hole 112 which intersects bore 104. By use of set screw 110, spring 108 can be threaded into bore 104 with set screw 110 being analogous to an internal thread. 
     As should be apparent, spring 108 functions in the same manner as glide post 24. Spring 108 extends below the bottom of the magnet or mounting bracket to raise the rear of the drill base when the magnet is not energized. When the magnet is energized, the magnet pulls the conical end 38 of reactor point 32 into the work surface and compresses or retracts spring 108 into bore 104. When the magnet is de-energized, spring 108 raises the rear of the drill unit and extracts reactor point 32 from the work surface. Additionally, the rounded wire of coil spring 108 permits easily sliding of the drill unit when the magnet is not energized. 
     As will be understood, various modifications may be made to this invention within the purview of the following claims. For example, the torque restraining device 10 may be mounted directly within the electromagnet 15 obviating the need for mounting bracket 12. Similarly, the bore 16 may extend from the bottom of bracket 12 or magnetic base 15 without extending through the top. If only a single partial bore is used, the glide post 24 could be retained within the bore by, for example, set screws or other retaining means which would permit the glide post to reciprocate within the bore. Additionally, the glide post of the present invention is readily adapted for use on any type of torque restraining device to protect the pointed end of the torque restraining point and to function as a glide post. As for example, in Hougen&#39;s prior patent &#39;673, the glide post of the present invention could be adapted for use on the torque restraining point as a protective sleeve and glide roller. Additionally, the coil spring of FIG. 6 could be used on the device of the &#39;673 patent. Other configurations may be used for the conical point of the reactor. Still further, the present invention is not limited to magnetic base drill. For example, the torque restraining device of the present invention could be used on a drill motor that is held in place by suction cups rather than an electromagnet. It will be apparent to those skilled in the art that the foregoing disclosures are exemplary in nature rather than limiting, the invention being limited only by the appended claims.