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A drill assembly and method for reducing plunge of a drill bit upon breaking through a workpiece. The drill assembly contains a motor to advance and retract the drill bit, the motor is controlled by a control unit in a feedback loop to achieve a desired stiffness. The control unit determines when th

A drill assembly and method for reducing plunge of a drill bit upon breaking through a workpiece. The drill assembly contains a motor to advance and retract the drill bit, the motor is controlled by a control unit in a feedback loop to achieve a desired stiffness. The control unit determines when the drill bit breaks through the workpiece and stops or retracts the movement of the drill bit.

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1. A drill assembly comprising: a drill body;a drill bit rotatably coupled to the drill body;a motor for advancing and retracting the drill bit relative to the drill body;at least one sensor for monitoring the advancement and retraction of the drill bit; anda control unit connected to the motor and

1. A drill assembly comprising: a drill body;a drill bit rotatably coupled to the drill body;a motor for advancing and retracting the drill bit relative to the drill body;at least one sensor for monitoring the advancement and retraction of the drill bit; anda control unit connected to the motor and at least one sensor, the control unit being configured to measure a change in speed of advancing motion of the drill bit relative to the drill body to detect breakthrough of a workpiece and, on detecting a breakthrough, control the motor to reduce plunge of the drill bit. 2. The drill assembly of claim 1, wherein the control unit monitors the at least one sensor to maintain a desired stiffness of the drill bit. 3. The drill assembly of claim 1, further comprising a support attached to the drill body. 4. The drill assembly of claim 3, wherein the support is a stabilizer extending from drill body to a workpiece to resiliently support the drill body. 5. The drill assembly of claim 4, wherein the control unit is configured to measure an increase in speed of the advancing motion of the stabilizer to detect breakthrough. 6. The drill assembly of claim 1, wherein the control unit is configured to measure an increase in speed of the advancing motion of the drill bit relative to the drill body to detect breakthrough. 7. The drill assembly of claim 1 wherein the at least one sensor is a microphone connected to the control unit, wherein the control unit is configured to measure a change in pitch from the microphone to detect breakthrough. 8. The drill assembly of claim 1 further comprising a second motor for rotating the drill bit, wherein the control unit is configured to measure a change in torque of the second motor to detect breakthrough. 9. The drill assembly of claim 8, wherein the control unit is configured to measure a reduction in power used by the second motor to detect breakthrough. 10. The drill assembly of claim 8, wherein the control unit is configured to control the second motor to maintain a constant rate of rotation of the drill bit. 11. The drill assembly of claim 8, wherein the control unit is configured to control the second motor to stop the rotation of the drill bit upon retraction. 12. The drill assembly of claim 8, wherein the control unit is configured to control the second motor to reverse the rotation of the drill bit upon retraction. 13. The drill assembly of claim 8 further comprising a variable trigger connected to the control unit to control the second motor to maintain a constant rate of rotation of the drill bit as selected by the variable trigger. 14. The drill assembly of claim 8, wherein the motors are selected from the group of pneumatic motors and electric motors. 15. The drill assembly of claim 3, wherein the stabilizer is spring loaded. 16. The drill assembly of claim 3, wherein the stabilizer is damping loaded. 17. The drill assembly of claim 4, wherein the stabilizer surrounds the drill bit. 18. The drill assembly of claim 4, wherein the stabilizer is transparent. 19. The drill assembly of claim 3, wherein the control unit is configured to stiffen the stabilizer upon breakthrough. 20. The drill assembly of claim 3, wherein the control unit is configured to actuate the stabilizer to move the drill body away from the workpiece upon breakthrough. 21. The drill assembly of claim 3, wherein the control unit monitors the at least one sensor to maintain a desired stiffness of the stabilizer. 22. The drill assembly of claim 1, wherein the control unit is configured to measure a displacement of the drill bit after the drill bit has made contact with the workpiece. 23. The drill assembly of claim 22, wherein the control unit is configured to retract the drill bit upon the displacement of the drill bit reaching a threshold. 24. The drill assembly of claim 1, wherein the control unit is configured for multilayer drilling. 25. The drill assembly of claim 1 further comprising an indicator to identify breakthrough. 26. The drill assembly of claim 23, wherein the indicator is a speaker connected to the control unit. 27. The drill assembly of claim 23, wherein the indicator is a light emitting device connected to the control unit. 28. A method for reducing plunge of a drill bit through a workpiece, the method comprising: initiating advancement of the drill bit towards the workpiece; anddetecting the drill bit breaking through the workpiece by measuring a change in speed of advancing motion of the drill bit relative to a drill body. 29. The method of claim 28 further comprising maintaining a desired stiffness of the drill bit. 30. The method of claim 29 further comprising retracting the drill bit on detecting the drill bit breaking through the workpiece. 31. The method of claim 29 further comprising stopping the advancement of the drill bit on detecting the drill bit breaking through the workpiece. 32. The method of claim 28, wherein detecting comprises measuring an increase in rate of advancement of the drill bit towards the workpiece. 33. The method of claim 28, wherein detecting comprises measuring a change in audible pitch from the drill bit. 34. The method of claim 28, wherein detecting comprises measuring a change in torque of a motor for rotating the drill bit. 35. The method of claim 30, wherein retracting the drill bit further comprises stopping rotation of the drill bit. 36. The method of claim 30, wherein retracting the drill bit further comprises reversing rotation of the drill bit. 37. A method for measuring penetration depth of a drill bit through a workpiece, the method comprising: initiating advancement of the drill bit towards the workpiece;detecting contact of the drill bit with the workpiece to begin measuring drill bit penetration;detecting the drill bit breaking through the workpiece to end measuring drill bit penetration, where the drill breaking through the workpiece is detected by measuring a change in speed of advancing motion of the drill bit relative to a drill body; andoutputting penetration measurement to a display.