1. Drilling Weight - Thechoice of drilling weight is determined based on the recommendations of the bitmanufacturer and the number of cutters on the hole opener.
2. Number of Cutters - Thenumber of cutters placed on a hole opener is governed by the following facts:
1) Maximum number which willfit around the perimeter.
2) The greater the number ofcutters, the less the weight, which therefore reduces the penetration rate)
3) In softer formations, lessweight is needed to penetrate.
4) The greater the number ofcutters, the smoother the tool will run.
5) The greater the number ofcutters, the greater the cost.
6) The greater the number ofcutters, the longer the cutters will last
3. Rotary Speed - Maximumspeed is determined by the manufacturer's recommendation and the calculation toaccount for the linear distance the cutter is moving per revolution
4. Hole Cleaning - Afrequently over looked point of hole opener operation is hole cleaning. Thevolume of cuttings to remove from a hole increase by a squared factor with anincrease in hole diameter.