Drilling Operation

Before commencing drilling ensure all the hammer threads are correctly tightened. The following table shows the correct torque that should be applied when tightening the hammer. Incorrect make up torque can result in thread damage. When threads are not tightened prior to drilling the percussion of the hammer combined with the rotation of the drill string results in over tightening of the DTH hammer. This can damage the threads and also lock the hammer preventing bit change and hammer maintenance.

Thread Torque
Hammer AD108RC AD116RC AD117 AD124
Torque 3100-3600 ft-lbs 5000-5400 ft-lbs 6500-7000 ft-lbs

The Reverse Circulation DTH Hammer will begin to operate as soon as the air supply is turned on and the percussion bit is firmly pressed into the rock face. The weight or thrust required to efficiently operate the hammer can be obtained from the weight on hammer chart. The effect of the drill rods weight on the hammer should also be taken into account when drilling. Insufficient thrust pressure will make the hammer drill erratically resulting in premature wear to the percussion bit and drive sub splines with damage to threads also likely to occur.

Sufficient thrust must be applied to the hammer to achieve optimum drilling rates. ADHB Reverse Circulation hammers produce significant energy which needs to be accommodated for when applying thrust to the hammer. The following table shows the required thrust.

As the hole gets deeper less thrust will be required as the drill string gets heavier. Eventually hold back will be required to prevent excessive weight on the percussion bit.