Powered tap driver with rotary control structure

[0001] This application relies for priority on Provisional Application Ser. No. 60/779,533, filed Mar. 6, 2006, entitled “Hand-Held Powered Tap Driver.”

[0002] “Tapping” is a cutting process in which a tap is rotated into a starting hole in a workpiece. The workpiece is usually metal, and the starting hole is usually slightly larger than the thread root diameter. The tap has threads formed thereon in a configuration corresponding to the threads to be cut in the workpiece. It is fluted to form cutting edges and provide for chip clearance. In workshop environments, when the starting hole is to be tapped, the tap is usually held in a tap wrench and is manually rotated while it is pressed into the starting hole. The tap must be started axially into the starting hole. The front, entry end of the tap is tapered so that the full cut of the threads is not taken by the first tap threads. This permits entry of the tap into the starting hole. The tap is rotated in the clockwise direction (for right-hand threads) and is pressed into the starting hole at the same time, which requires care and dexterity.

[0003] After chip cutting is started and chips are forming, it is desirable to rotate the tap in the unscrewing direction to break loose the cut chips. When there are four flutes on the tap, it is desirable to advance the tap in the cutting direction more than half a turn and then back and out more than a quarter turn. In workshop environments, tapping has previously been done by hand. It is desirable to provide a hand-held powered tap driver for an artisan or a workman. The hand-held powered tap driver should be light and easy to handle so that an artisan can easily and quickly create tapped holes.

[0004] In order to aid in the understanding of this invention, it can be stated in essentially summary form that it is directed to a hand-held powered tap driver which has a body. The body has a drive shaft which carries a tap chuck for rotation around the axis of the drive shaft. A motor is mounted in the body and is connected to drive the drive shaft. A manually accessible switch on the body causes energization of the motor. The energization is such as to cause rotation of the tap in the tapping direction. A control circuit periodically causes reversing of the tap to partially withdraw it from the tapped hole to break the chips. When tapping is complete and the workman wants to withdraw the tap, he presses a reverse switch which rotates the tap out of the tapped hole.

[0005] It is thus, a purpose and advantage of this invention to provide a hand-held tap driver which is easy to use and which conveniently presents a tap to a hole and drives it in tapping manner into the hole.

[0006] It is another purpose and advantage of this invention to provide a hand-held tap driver wherein energization in the forward direction is caused by actuating a switch on the body of the tap driver, and withdrawal of the tap is accomplished by actuating a reverse switch which rotates the tap out the tapped hole.

[0007] It is another purpose and advantage of this invention to provide a hand-held powered tap driver which automatically makes intermittent forward cutting rotations of the tap interspersed with reverse motion of a smaller angular amount so that the tap is intermittently forwardly driven to tap a hole in the workpiece.

[0008] It is a further purpose and advantage of this invention to provide a hand-held powered tap driver which senses the tapping torque and when the tapping torque reaches a selected value, reverse rotates the tap for less than one turn to loosen the chips.

[0009] It is another purpose and advantage of this invention to provide a unitary structure which contains all the necessary equipment in a hand-held body so that tapping can be accomplished by appropriately pressing the tap into the starting hole and actuating forward and reversing switches to accomplish tapping and removal of the tap from the tapped hole.

[0010] Other purposes and advantages of this invention will become apparent from a study of the following portion of the specification.

[0016] The hand-held powered tap driver of this invention is generally indicated at 10 in FIG. 1. It has a body 12 which is sized and configured to be conveniently held in the hand. In FIG. 1, the near cover of the body has been removed to show the interior structure. When the driver 10 is complete, the devices seen in FIG. 1 are enclosed. Drive shaft 14 is rotatably mounted in bearing 16 at the tap end of the body. Drive shaft 14 carries chuck 18 in which tap 20 is removably mounted. Shaft 14 is connected to motor 22 and is rotatable in bearing 16. The motor 22 is reversible.

[0017] Body 12 contains a power supply, which may be an external plugin to a central supply system. However, in order to be completely portable, the power supply is preferably a battery 24. The battery 24 is preferably a rechargeable battery with a suitable external tap 25 for connection to a recharging source. The battery is connected through line 28 to the control switch 26, see FIG. 2. Control switch 26 is a double-throw switch with the unactuated position being normally off. The control switch 26 is a rocker switch with its rocker 30 being rockable downward toward the tap 20, see FIG. 1, or upwards. When rocked downward, the switchblade 32 energizes line 34 to signal forward rotation of the motor 22 to cause the tap to rotate in the clockwise, cutting direction. The energization of line 34 acts through reversing circuit 36 which initially energizes line 38 to rotate the motor in the forward, tapping direction.

[0018] As discussed above, it is desirable to reverse the tap at appropriate times to break loose the chips which are cut during tapping. As seen in FIG. 2, timer 40 is connected to the reversing circuit through switch 42. Switch 42 is normally closed. As tapping proceeds, the timer 40 actuates the reversing circuit to reverse the motor and the tap for a short time period. When this occurs, the tap reverses long enough in time and far enough in rotation to break loose the chips. A one-quarter revolution is all that is necessary. After the timer 40 times out, the reversing circuit 36 drives the motor in the forward direction as long as the rocker switch is actuated to energize line 34. As long as the rocker switch is in this position, the tap rotates forward for a time predetermined by timer 40. This time is preferably sufficient to provide for about one turn of the tap. When the timer times out, reversing occurs for the time equivalent to about one-quarter of a reverse turn. When tapping is complete, the rocker switch is actuated to energize line 35 to reverse the tap out of the newly tapped hole. In the reverse direction, the timer 40 is not effective.

[0019] Switch 42 is provided so that this timed reversal does not occur. When timer switch 42 is open, the motor rotation is controlled only by rocker switch 26. This is useful when tapping thin metal. It is also useful for driving devices other than taps, such as screws or drills.

[0020] FIGS. 3, 4 and 5 illustrate an embodiment of a tap driver 50 which has most of the same physical characteristics. In this embodiment, the reversal of the tap is directed by torque instead of time. Torque is sensed by motor current in line 38 with the sensor line 52 connecting the motor current signal to the motor current sensing circuit 54. The motor current and motor torque are related. The torque should be selectable, in accordance with tap size and material being tapped. There are other factors which influence the amount of tapping torque, but these are the most significant ones. In order to accommodate for these differences in tapping torque, an external torque selecting knob 56 is provided. This adjusts the potentiometer 58, which is supplied from a constant voltage circuit, see FIG. 5. The motor current signal and the torque set point signal are compared in comparator 60. When the torque reaches the preselected set point, a signal in line 62 causes reversal of the reversing circuit 36. Now, the motor is energized by reversing circuit 36 to rotate in the tap unscrewing direction. It is desirable that the tap rotate in the unscrewing direction for about a one-half turn to break loose the chips, to reduce the tapping torque.

[0021] Timer 66 permits the motor to drive the tap in the unscrewing position for about half a turn. Thereupon, the timer times out. Since low forward torque is sensed, the torque sensing circuit 54 energizes the motor 22 to rotate in the tapping direction. This forward tapping rotation continues until the torque set point is reached, whereupon a reversal again takes place. This action continues until the workman has determined that the tapping is complete. When tapping is complete, the workman releases the rocker 30 from the forward, tapping position and rotates it upward to the tap removal position. In this position, the line 35 is energized. This causes the reversing circuit 36 to rotate the motor 22 in the tap unscrewing direction. As long as the rocker switch is in this position, the motor continues in that rotation to rotate the tap free of the newly tapped hole. For convenience, most of the circuitry can be collected together and mounted in a control circuit board 64.

[0022] This invention has been described in its preferred embodiment, and it is clear that it is susceptible to numerous modifications and embodiments within the ability of those skilled in the art. Accordingly, the scope of this invention is defined by the scope of the following claims.