Mechanical disconnect for rotation drive

1. A method of using a horizontal directional drilling system, the system comprising:

an exit-side horizontal directional drill comprising:

a rotationally-driven spindle coupled to a drill string;

a rotary motor having an output shaft; and

a rotational disconnect configured to transfer torque between the output shaft and the spindle when engaged, and to prevent the transfer of torque between the output shaft and the spindle when disengaged; and

a pilot horizontal directional drill;

in which the drill string is disposed between the horizontal directional drill and the pilot horizontal directional drill;

the method comprising:

pulling and rotating the drill string with the pilot drill; and

simultaneously, pushing the drill string with the exit side drill while the output shaft and spindle are not rotationally coupled.

2. The method of claim 1 wherein the exit-side horizontal directional drill further comprises an arm configured to disengage the output shaft and the spindle.

3. The method of claim 1 wherein the exit-side horizontal directional drill further comprises a rotary brake disposed between the rotational disconnect and the spindle.

4. The method of claim 1 wherein the pilot horizontal directional drill comprises:

a second rotationally-driven spindle coupled to the drill string;

a second rotary motor having a second output shaft; and

a second rotational disconnect configured to transfer torque between the second output shaft and the second spindle when engaged, and to prevent the transfer of torque between the second output shaft and the second spindle when disengaged.

5. The method of claim 1 wherein the system further comprises a backreamer positioned along the drill string between the horizontal directional drill and the pilot horizontal directional drill.

6. The method of claim 5 wherein the drill string between the backreamer and the horizontal directional drill defines a first diameter and the drill string between the backreamer and the pilot horizontal directional drill defines a second diameter, in which the second diameter and first diameter are unequal.

7. The method of claim 6 wherein the first diameter is greater than the second diameter.

8. A method of installing an underground pipe using a system comprising:

a pilot horizontal directional drill;

a pilot drill string having a first end and a second end, wherein the first end is operatively connected to the pilot horizontal directional drill;

a backreamer attached to the pilot drill string at its second end;

a first product pipe section; and

an exit side horizontal directional drill comprising a motor-driven spindle;

wherein the method comprises:

rotating and advancing the pilot drill string to an exit point using the pilot horizontal directional drill;

thereafter, attaching the backreamer to the pilot drill string;

rotating the first product pipe section wherein such rotation attaches the first product pipe section to the backreamer using the motor-driven spindle supported by the exit side horizontal directional drill;

thereafter, decoupling the motor from the spindle of the exit side horizontal directional drill;

thereafter, pulling and rotating the backreamer using the pilot horizontal directional drill; and

simultaneously with the step of pulling and rotating the backreamer, pushing the first product pipe section into the ground with the spindle of the exit side horizontal directional drill.

9. The method of claim 8 further comprising:

after pushing the first product pipe section into the ground, coupling the motor to the spindle of the exit side horizontal directional drill;

disconnecting the first product pipe section from the spindle;

thereafter, connecting a second product pipe section to the spindle;

rotating the second product pipe section with the spindle in order to connect the second product pipe section to the first product pipe section; and

thereafter, decoupling the motor from the spindle of the exit side drill.

10. The method of claim 8 wherein the step of decoupling the motor from the spindle of the exit side horizontal directional drill comprises:

disconnecting an input shaft from an output shaft in a mechanical disconnect disposed between the motor and the spindle.

11. A method of using a drilling system, the drilling system comprising:

a pilot drill;

a pilot drill string having a first end and a second end, wherein the first end is operatively connected to the pilot drill;

a drilling tool attached to the pilot drill string at its second end;

a product pipe attached to the drilling tool;

an exit side drill comprising:

a spindle operatively connected to the product pipe;

a motor configured to rotationally drive a shaft; and

a rotational disconnect configured to transfer torque between the output shaft and the spindle when engaged, and to prevent the transfer of torque between the shaft and the spindle when disengaged;

wherein the method comprises:

pulling and rotating the pilot drill string with the pilot drill;

simultaneously, pushing the product pipe with the exit side drill while the spindle and shaft are not rotationally coupled.

12. The method of claim 11 further comprising:

after pushing the product pipe with the exit side drill, ceasing rotation of the pilot drill string;

thereafter, coupling the spindle to the shaft; and

thereafter rotating the spindle to attach a product pipe segment to the product pipe.

13. The method of claim 11 wherein the pilot drill and exit side drill are positioned above ground and the drilling tool is located underground.