Correct rotation speed has a direct effect on both bit life and hammer performance. Proper rotation is essential for long hammer and bit life. Some common elements involving rotation speed are:

• Bit Life

1. Rotation Too Slow - The main purpose of rotating a down hole hammer and bit is to index the carbide button inserts to fresh rock on every impact. If the rotation is too slow the buttons may tend to bury themselves and this will result in an erratic rotation. Slow rotation can also result in the recrushing of the rock, also known as regrinding, which results in a rapid carbide wear.

2. Rotation Too Fast - Increasing the rotation speed will not necessarily increase the penetration rate. It will usually result in rapid gage carbide wear due to the high scraping forces rather than a crushing force.

• Hammer Performance

Rotation when drilling with a down hole hammer serves only two simple purposes.

1. Turning in a clockwise direction keeps the tool joints tight.

2. Rotation indexes the carbide buttons to fracture fresh rock with each impact.

   Note: Reverse rotation and impact without rotation may cause tool joints to become loose. Loose joints may cause drilling equipment to break free and be lost down the hole.

An operator must learn to have a feel for finding the proper rotation speed that will deliver optimum penetration rate without sacrificing bit life. As a starting point an operator can use the following:

       R.P.M. = 1/2 Penetration rate per hour in Feet.

       R.P.M. = 1.6 X Penetration rate per hour in Metres.

As an example, if the average penetration rate is 60 feet (18.3 m) per hour the revolutions per minute should be around 30 (29.3).