Air Drilling Handbook was written by H. Van Ormer and published in 1987. It contains 167 pages. It’s still available, and is the best book I’ve read on hammer drilling.
Drilling HammersMy experience with down-hole hammers has been self-taught, and usually has come only after making many mistakes.
The first thing with hammer drilling is to have the drill set up perfectly level. The next is to rotate the hammer slowly enough so that each stroke of the hammer hits a new spot. I’ve been told that approximately 20 rpm is best. After a time – and a few bits – you get a feel for your preferred rpm. Too slow wears out the bit prematurely, and too fast can cause the buttons to shear or break. There are some hammer bit companies that supply manuals with photos of bit wear and the reasons for each type of wear. An indication of a severely worn bit is a squealing sound coming from the hole.
You learn the downward feed by the sound of the hammer. Generally, after a few feet of drilling, you start holding back instead of pulling down. With the proper hold-back, you will have a straighter hole. Most times, at 700 feet, I can rotate the drill stem by hand while it’s suspended on the hoisting line. Now that’s a straight hole. If the hole is straight, you usually can see the water in the hole by using a mirror reflecting the sunlight down the hole. An indication of a crooked hole is when the drill stem rotates hard or is jerky when lifting up or down when not rotating.
Adding water keeps the dust down. Too little water injected can cause dust to build up on the hole walls (wall cake). Too much water is just a mess and a waste. Again, you will find what works best for you with experience. The advantage of adding mud, foam and polymers is gained by experience in the geographical area that you drill. I suggest that you contact your favorite mud supplier for assistance and recommendations. That’s what they do.
Most down-hole hammer drills include a hammer oiler. To extend the life of your hammer, it is important to keep oil in the oiler, and be sure oil is constantly injected into the drill stem.
The best way to do hammer drilling is to purchase a hammer and start drilling – you will gain experience fast.
Roller-cone BitsIn hard rock, turn the bit slow and apply lots of weight. In clays, shales and unconsolidated (sand) formations, turn the bit fast with medium pull-down pressure.
Long-tooth bits are for soft formations, while short-tooth bits are for medium formations. Short-tooth bits with webs on the outer teeth are for hard formations. Tungsten carbide insert (TCI) roller-button bits are for very hard formations. These bits require a lot of weight to drill properly.
Drag Bits Aid StabilityI think one of the most important things when drilling in sands and sticky clays is to have a mud ring welded around the bit, just smaller than the outer cutting edge of the bit. It keeps the bit from wobbling in the hole when rotating and not drilling (usually making a larger hole). When coming out of the hole, the ring will slice off wall packs (boots) in the hole, allowing them to fall to the bottom of the hole, or it will pull the boot out of the hole ahead of the bit. This allows the geothermal loops, casing and/or pack sand to reach the hole bottom easier.
I like long reaming sides on drag bits about 8 inches to 12 inches long. They provide a stabilizing effect in the event you don’t run a stabilizer above the bit. This helps keep the hole straight, and prevents doglegs in the hole, allowing your geothermal loops, casing and pack sand to enter the drilled hole more easily.
Cable-tool BitsCable-tool drilling is becoming a lost art, however, it works anywhere in the world. The drilling tools and bits are many, and each driller has his own preference.
About cable-tool button bits, these bits are somewhat new to cable-tool drilling and preferred by those who have used them. They are manufactured in United States and Brazil.