Getting the Drill Ready
Be certain the drill operator is familiar with the drill unit, particularly with safe drilling practices. Be sure the entire drill rig has been properly lubricated. Have sufficient drilling accessories and tools on hand to meet your requirements. Inspect drilling accessories for damage during shipping. Keep rock bits in their containers, under cover and clean. Keep bits from colliding during transportation, as tungsten carbide inserts can chip if they strike one another. Set drill steel on wooden planks or horses to protect them.
Make certain the striking face of the hammer is square and true. Check to see that it is not beveled, worn or chipped, as this can rapidly ruin a new shank. Check the chuck bushing for wear and proper fit with the shank. Check the shank end to be certain it is square and not worn or chipped. A damaged shank can ruin the drill piston and the drill. Start the drill at low throttle and make certain the lubrication is working.
Starting the Drill
Position the drill on firm footing before you start to drill. Maintain alignment as you collar the hole. Misalignment can cause stuck steel; broken shanks, couplings or steel; and excessive wear of drill chuck parts and the bits.
Collar the hole properly. Be certain the mast or guide shell is firmly supported against the ground or the face and the centralizer is closed. Begin drilling oh a tight feed and a low throttle. After the bit has buried itself, open up the throttle and adjust the feed.
Maintain enough rotation for good penetration Excessive rotation will wear the gauge of the bit.
Maintain Correct Feed Pressure
Insufficient Air Pressure
If you have insufficient air pressure, you will be unable to maintain sufficient feed pressure. This will result in a loose drill string which will prematurely wear threads and bits. Excessive heat will generate in the drill string and wear the drill parts.
Sufficient Air Pressure
With sufficient air pressure, always keep the bit against the bottom of the hole while drilling. Maintain enough pressure on the bits to keep it from bouncing on the bottom.
Too Much Feed Pressure
If too much feed pressure is applied, the steel will buckle and bind in the hole and stop rotation.
In hard rock, over-feeding will reduce penetration. Penetration is slower in hard rock and the feed pressure must be reduced accordingly.
Don't over-feed in soft rock either. You may bury the bit and hang the steel. If you must reduce feed pressure in soft rock, remember to reduce the hammer throttle also.
Keep the Hole Clean
In deep hole drilling, blow the hole frequently. In soft ground or where seepage occurs, a mud collar can form or the steel can hang up. With every rod added to the string, blow the hole. This way, you will know if you have a plugged steel.
Do Not Allow the Drill to Diesel
This will happen if you are operating the drill with insufficient feed pressure. It can also happen when running the hammer at full throttle while withdrawing the bit. Dieseling is caused by burning drill oil. This heats up the drill and burns off the lubricant. The result can be a destroyed hammer. To stop dieseling, slow down the drill throttle and increase feed pressure.
If you must change bits while drilling a longhole, always remember to put a smaller bit on to follow the starter bit. Otherwise, the steel can become jammed and the bit pinched and broken.
Care and Maintenance
Whenever possible, use new bits with new steel. If new bits are used on worn steel, excessive thread wear will develop on the bit. Threads can be prematurely worn on the drill steel if used with worn bits. Use thread lubricant in the couplings and in the bit. The thread lubricant should be covered to avoid contamination with dust and dirt. The shank, coupling, drill steel and bit threads should be kept clean. This will yield maximum life from all drill string components.
Make certain all joints are kept tight on the drill string. Threads are intended to keep the components together. They are not designed to transmit the energy of the hammer. The drill steel ends must contact each other firmly in the coupling and contact the bottom of the rock bit. In many locations, primarily in mines or tunnels, water can be highly corrosive. This and other corrosive materials can form corrosion pits which result in fatigue failures. This corrosion can also shorten the life of rock drill parts. If rust or corrosion occurs, clean it off thoroughly and apply protective oil or grease.
If drill rods and couplings are dropped or thrown, small nicks, notches and dents can start fatigue cracks that will cause early failure. Do not hammer on drill steel or use drill steel sections for prying, propping or as a lever.
Rotate drill steel. When using sectional drill steel, rotate the steel so that thread life will be even throughout the drill string. It is also helpful to turn the steel end-for-end to equalize thread wear.
Check the threads of the drill string and discard when worn. It is false economy to try to get every last bit of life from the thread. Referring to the earlier tip, try to keep new rods with new steel. Replace components that have spalled threads or damaged rod ends. Keep all threads clean to resist un-necessary thread wear from dirt and grinding dust.
If couplings become over-heated or joints are so tight they will not come loose, something is wrong. Look for dulled bits or worn threads on rods and couplings. Excessive feed pressure can jam couplings.
To remove rock bits, do not beat on them with a steel hammer. The tungsten carbide inserts can shatter or nicks in the body can result in split or wrung-off bit bodies. Use a bit wrench or "rattle" bits loose by running the drill at low throttle and no rotation.
Remember to recondition bits periodically. Greater penetration, production, drill life and drill string life can be obtained when drilling with sharp bits.
If a bit breaks while drilling a hole, be certain you can flush all particles out of the hole, especially steel or tungsten carbide. If you can't, abandon the hole. Drilling against broken carbide or steel guarantees another broken bit.
In abrasive rock, cross face bits can wear to a square shape and drill a rifled hole in a long spiral pattern. If this occurs, it is difficult or impossible to withdraw the bit and steel. When this happens either gauge grind the cross bit back to its original circular shape or throw it away. Using an X cutting face bit will avoid rifling.