Percussive or hammer drilling is most often used to drill rock. In Forest Service trail work, gasoline-powered hammer drilling is common. Hand drilling is sometimes necessary however, because machines cannot be used. This manual describes elementary tools and techniques for hand drilling rock.
Although hand drilling is slow work, it is a safe and simple way to prepare rocks for breaking with explosives, wedge and feather sets or expansion chemicals, or to accept anchor bolts. The driller drives the steel by methodical hammering and turning. When the hammer strikes the head of the steel, the bit is forced against the rock. After each blow of the hammer, the driller turns the steel slightly and strikes it again. With each blow the bit chips small amounts of rock that collect in the hole as "drilling dust." The driller removes the dust by adding water to the hole, which creates a mud that sticks to the sides of the steel. To clear the mud, the driller removes the steel and raps it against the rock. The procedure is continued until the hole is deep enough; longer steel is substituted as the hole lengthens.
The steel is manipulated with one hand while the other hand hammers (single jacking), or the steel is manipulated by two hands while another person hammers (double jacking). This manual describes correct techniques, discusses proper tool maintenance, and includes sources of tools and a bibliography.
Although hand drilling is not commonly used in the Forest Service, it can effectively remove rock from trails and does observe the Chief's directive to resurrect, develop, and utilize primitive skills in wilderness management. Hand drilling skills have been all but forgotten; we hope to preserve them with this manual.
No cost comparisons have been made between hand drilling and gasoline-powered drilling. Initial tool costs are much less for hand drilling, however, and the techniques can be learned by unskilled or low salary employees. Since gasoline-powered drills are prohibited in wilderness, hand drilling allows wilderness managers to maintain trails without violating wilderness guidelines.
Hand drilling is an effective method for maintaining forest trails.
Description of Tools
Hand Drilling Steel
|Rod||The rod is high carbon octagonal steel bar, 3/4 to 7/8 inches wide. Length may vary from 10 inches to several feet.||
Star pattern bit
|Bit||The bit is the sharpened end of the rod.|
|Bit Gage||The cutting edge is flared on 7/8 inch steel to a length of 1'/4 inches.* Other thicknesses of rod have similarly proportioned cutting edges.|
|Effective length||The effective length is the length of the steel that is available for drilling, the total length less the shank or hand hold area.|
|Shank||The shank is the area near the head where the driller or holder grips the steel.|
|Head||The head is the end of the rod opposite the cutting edge, and receives the blow of the hammer.||
Straight pattern bit
|Plastic caps||These are convenient for protecting sharpened cutting edges during transportation and storage. The top cap also keeps ragged edges from snagging other items.|
|Cutting edge angle||This angle must be precisely maintained during sharpening and reconditioning so the cutting edge remains in the center of the rod.|
|Star Pattern Bit||Two perpendicular cutting edges, flared and raised slightly, intersect at the center of the bit. These are common on modern drilling steel.|
|Straight Pattern Bit||These have a single flared, slightly raised, cutting edge. They are old style bits, and may be found in second hand or antique stores.|
*We have not arbitrarily chosen this size rod. Water gels approved for Forest Service blasting are packaged in polyester cartridges. The length of these varies, but the smallest available diameter package is 1 inch. A 1 1/4 inch hole is the minimum size that could easily accept that package.
Hand Drilling Hammers
|Head||The double face hammer head is made of heat-treated, high carbon steel.||
|Striking faces||The two striking faces should have beveled edges and should be heat treated.|
|Handle||Wood handles are usually made of hickory. They should have a tight, knot-free grain that runs parallel to the wedge slot. Other handles are made of fiberglass, or are a forged extension of the head.||
|Single jack||These are also called 'club' or hand drilling hammers. Handles are commonly 10 inches long, and heads weigh either 3 or 4 pounds. The short handle is uniquely suited to hand drilling because it resists breaking better than longer ones, and it facilitates accuracy by requiring the hand to be close to the head.|
|Engineer's hammer||These are also called long handle single jacks. They come with a 14-inch handle attached to a 3- or 4-pound head, and work well for the drilling technique we call modified double jacking.||
|Double jack||These large driving sledges have 36-inch handles and 6- or 8-pound heads. Because their use requires considerable expertise from both the driller and holder, we recommend that you use single jacking or modified double jacking until safety and proficiency with the double jack can be assured.|
Wedge and Feathers
|Wedge||This is a heat-treated steel rod that is generally the same diameter as the drilling steel.||
Wedge and feathers
|Blade||Wedges have a pointed, flattened blade opposite a head that receives the blow of the hammer.|
|Feathers||These are half round pieces of forged steel with a curved top, blunt bottom, and a flat inside edge running their entire length.|
A proposed trail may cross a rock face or, after prolonged trail use, hazardous points of solid rock often protrude into the tread. A trail is built in rock by cutting some rock away to form a ledge or by removing the rock entirely. Sometimes rocks may be chipped flat with a pick.
Hand drilling helps remove rock three ways: (1) A rock may be split into chunks of manageable size by steel drilled into a natural seam; (2) If the steel in the seam does not split the rock by itself, the hole may be fitted with the wedge and feathers. The wedge is driven between the feathers with a hammer until the rock breaks; (3) Finally a hole may be used to prepare a rock for blasting. In general, the larger the rocks, the more likely you will use explosives to move them.
Although most large rocks are moved with explosives, we will not discuss the safe and effective use of explosives in this manual. For this information we recommend the Forest Service Blasters Handbook.¹ Explosives are most efficient, however, when used in drilled holes.
There are several considerations that make hand drilling a preferable alternative to other drilling. Gasoline-powered rock drills are expensive, and trail operations often do not have enough drilling work to justify costly equipment. Moreover these machines are noisy, heavy to backpack into remote areas, and tedious to use when they are there. Ferrying in gasoline-powered drills and supplies must usually be coordinated with a packer. And since motorized equipment is prohibited in wilderness, permission to use power drills must be secured in advance.
In short, many small drilling jobs are delayed because of economic, logistical, or policy considerations. Personnel trained to use hand drilling equipment could accomplish these small drilling jobs economcially without violating the spirit of the 1964 Wilderness Act.
The building blocks for the Egyptian pyramids and obelisks were obtained by using hammers and wooden wedges to extract large sections of stone in carefully measured shapes and sizes. The wedges had a hole in the middle for holding and carrying.
Miners from the time of the Roman Empire though the Middle Ages often applied a "fire setting" system to break rock. A rock face was exposed to intense heat followed by a quick dousing with water. The sudden cooling caused the rock to crack and split along natural seams. Sometimes a suspended wooden ram with a hard stone ball on its front was used to open a hole in the center of a rock face, and the face was chipped into it radially.
Gun powder was first used to break rock during the Middle Ages. In 1683 a Saxon named Hemming Hutman used a drill forged of wrought iron with an inset bit of tempered steel to hammer holes in the rock at critical points. The charges placed in the holes broke the rock more effectively than those laid on or near it.
The early history of our country contains many accounts of legendary 'hammer and steel' drillers who were experts at both single and double jacking. Single jacking involved an individual holding and turning the steel with one hand while hitting the steel with a small hammer held in the other hand.
Single jack drilling, circa 1850. (Photo reprinted
courtesy of Compressed Air Magazine.)
Ambidexterity was very helpful for the single jack driller because he could work longer by shifting the hammer from one hand to the other to distribute the work. In double jacking one or two drillers hit a drilling steel with large sledge hammers while a holder turned the steel slightly after each blow. As the hole deepened, the holder substituted longer steels in a way that did not interrupt the driller's disciplined rhythm.
|'Down hole' double jacking, early 1800's.||'Up hole' double jacking, early 1800's.||A prospector single jacking, circa 1910.|
|(Photos reprinted courtesy of Compressed Air Magazine.)|
Since every mechanical advantage gained by drillers was considered desirable, hand drilling was generally abandoned as soon as pneumatic drills were developed. Still some hand drilling methods were retained by prospectors for small budget rock work. Drilling and breaking rock with hand tools is discussed in Forest Service manuals up to 1923, and in prospecting handbooks as recently as 1943.
Some of the older techniques are not applicable today. For example, we consider double jacking unsafe for inexperienced drillers. Since most of today's hand drilling will be done by beginners, we suggest you use either single jacking or modified double jacking, a technique we developed. Both of these methods are safe, effective, and readily learned.
Every section of rock has its own character, and experience and common sense will help determine the most effective method of dealing with it. Take time to carefully evaluate the rock's structure. Consider whether the rock is solid or 'seamy', stratified horizontally or vertically, or is igneous, sedimentary, or metamorphic before deciding where and how to attack it. Work with, not against, the rock.
The importance of properly planning the hole in advance, that is, deciding where and how deep to place it, cannot be overemphasized. Rock usually splits to the first horizontal seam below the drill bit or tip of the wedge. Proper placement will help assure that the rock will break at the proper angle and in the right place while using the least time and energy. Using the shortest steel necessary will also save time and energy.
Courtesy of the University of Montana
Mansfield Library Archives.
¹U.S. Department of Agriculture Forest Service. 1980. Blaster's Handbook. FSH 7109.51, 146 p. Washington, D.C.