Logo Picture Left SideLogo Picture Right SideLogo Text at Center
Home > Search > Site Map > Georgia > Elberton Granite

Elberton Granite
The Quarrying and Manufacturing Process

Elberton Granite Logo


Prepared by Elberton Granite Association, Inc.1
P. O. Box 640, Elberton, Georgia 30635


(The following is reproduced with permission of Elberton Granite.)


The Quarrying Process

Basically, granite quarrying involves cutting channels on all sides of large, rectangular sections of granite called quarry blocks. These blocks usually have an open face, and once the ends and backs of the doorstep-like ledges are channeled loose, horizontal lift holes are drilled along the bottom of the open face. The holes are then loaded with primer cord explosive and the resulting blast has just enough force to break the quarry block from the bed of the quarry. Then jackhammers drill 3-in.-deep holes about 6-in. apart the length of the block and steel wedges and shims are inserted in the holes. The wedges are hit with sledghammers and the long length of granite cracks loose. This section is then cross-cut by further drilling and wedging into individual saw blocks, usually three to four feet wide, three to four feet high, ten to twelve feet long, and weighing nine to ten tons. The dimensioned saw blocks are removed by derrick or mobile crane and shipped to monument plants for processing.

During the initial quarrying stage, when the long quarry blocks are being freed from the surrounding mass, several different methods are used by many quarries. These techniques include jet burner channeling, diamond wire sawing, and drilling-blasting.

Currently, the prevailing method is jet burner channeling. The burner is actually a miniature rocket motor attached to a long steel pipe which burns a pressurized mixture of fuel oil and air. The system is aptly named the "jet burner", for the flame leaves the pressurized combustion chamber at approximately five times the speed of sound, or 4,000 feet per second and generates a heat of 2,800 degrees Fahrenheit. The flame causes the granite to disintegrate or break down into small flakes or a dust as the heat crystallizes and expands the granite. The burner cuts a 4-in. wide channel as the heated granite flakes off each time the flame passes over a given area. Only the flame comes in contact with the stone and there is no damage to adjacent surfaces. Using the burner, it is possible to cut a vertical channel 12 to 15 feet deep at a rate of about 14 square feet per hour.

A newer method, which is really a modernized version of an old-style drilling method, uses a combination of burning, drilling, and blasting, to free the large, rectangular quarry blocks. In this method, burners still channel the blocks on the ends and blasting may still be used to crack the blocks loose on the bottom; but instead of using jackhammers, wedges and shims, to cut the granite into smaller sawblocks, a high-speed track drill sinks rows of holes 4 to 6" apart in which primer cord or pipe charges of explosive are strategically placed and when detonated split the sections loose. The high-speed drill bits penetrate the granite at a rate of up to three feet per minute and blocks up to 9-feet. Wide and 60 ft. long and 10-ft. deep will "jump" 18 inches or more from the surrounding mass when the powder charges in the vertical holes are detonated. This method, say quarriers, is twice as fast as using burners and drills exclusively.

The latest technique to free the boxcar-sized quarry blocks is the diamond saw which basically consists of an engine pulling wire cable through a system of pulleys and return wheels. The wire is a steel cable on which diamond grit-impregnated beads are held in place by plastic spacers. The wire saw strand is threaded through intersecting vertical and horizontal holes; the wire is jointed together making a large loop which simultaneously cuts the top, bottom, and one end of the granite mass. Water is fed continuously through the narrow cuts to cool the wire.

If a ledge has two open sides, the wire saw can cut the entire block free. However, the attached side must still be channeled with a burner or drilled and blasted free. Quarriers say the wire sawing method will cut 35 to 40 square feet of granite per hour, or four to five times faster than a jet burner.

Now that the whole section is free on all sides and the bottom, the jackhammers and plug drills will follow a chalk line down the block, placing small vertical holes 3" deep along the line. The length of the block has been determined by the size the quarry foreman needs to fill an order. An average-size saw block of rough granite ten feet long, three feet wide, and three feet high contains ninety cubic feet of stone weighing approximately 225 pounds per foot or a total weight of 20,250 pounds. All holes are now drilled and ready for the wedge and shims to be inserted. The wedge is a 3' piece of tapered steel placed between two shims in each hole. The quarry worker uses a sledge hammer and follows down the long row, tapping each wedge and forcing the pressure from the wedge to the shims, causing the granite to break evenly as though it were a block of wood.

The entire saw block is now free. Large hooks are placed in holes drilled in each end of the block. A derrick boom is slowly raised, tightening the hooks in their holes and the block is lifted from the quarry to be placed on a waiting truck for transporting to the manufacturing plant.

After careful examination, the granite selected for finishing is started on its way through the various manufacturing processes. The remainder-more than 60 percent of all Elberton granite quarried-is discarded on mountainous "grout" or waste piles. Because standards for monumental grade are so high, only the best can be used.

The Manufacturing Process (Sawing Methods)

To transform the huge block of rough granite into smaller pieces for manufacturing, the block must be sawed into "slabs". These slabs are usually cut into 6", 8", 10" and 12" thicknesses. In Elberton, there are three types of saws: the diamond rotary saw, the gang saw, and the wire saw. The diamond saw is a revolutionary new machine, and Elberton's granite manufacturers were among the first in the nation to utilize them.

The diamond rotary saw is usually equipped with a 9, 10, or 11-foot diameter solid steel blade impregnated with 140 or more industrial diamond segments. Tons of fresh water are used to cool the saw blade during operation. It will consistently cut an average of 23 to 25 square feet of Elberton Blue-Gray Granite per hour, and can be programmed to operate around-the clock by pre-setting the height and length of the blocks to be cut and the desired thicknesses of the slabs.

Gang saws use fine steel shot and dozens of thin blades powered by pitman drive and flywheel assemblies to operate the huge saw mechanisms primarily used to produce thin structural stone panels. Large pumps in pits below the saws maintain a constant flow of water and steel shot slurry onto the block being cut. The saws hold up to 10 elongated blades, but usually only around 70 or so blades are used to saw -in. to 1-in.-thick panels.

The versatile wire saw is a commonly-used device and accomplishes many "cuts" in granite. A small " spiral steel wire together with abrasives and water cuts the block at the rate of approximately 13" per hour. Some wire saws may contain several strands of wire totaling more than a mile in length. Smaller single-strand wire saws are used in the manufacturing plants to do a variety of sawing jobs. The intricate contour wire saw can cut perfect crosses or other geometric patterns through the granite. The wire follows a heavy plywood pattern as it zig-zags in cutting the design.

The Polishing Process

After most slabs are sawed, they are polished to a high gloss by automatic or manually-operated machines which grind, hone and buff the granite surfaces with water and abrasive grit or polishing bricks.

Many monument manufacturers now use computerized polishing lines utilizing abrasive bricks of varying grits to achieve the glass-like polish. These bricks, usually four or five, are mounted on grinding heads which revolve at high speeds. There are two types of automatic polishers. One is a computer-operated, gantry-type mounted on rails allowing the machine to move over an elongated bed in which 12 or more slabs can be placed. The polisher may be a single or twin head system on which the abrasive bricks are mounted to polish each slab individually. The heads are equipped with sensors which keep them from running off the edge of the slabs as they spin and traverse back and forth across the surface. The abrasive bricks on the polishing heads have to be changed as different grit sizes are required for different stages of polishing.

The other type of automatic polishing system is the continual line polisher. The slabs are on a large continually-moving conveyor belt and emerge from the polisher completely polished in a few minutes. Like the gantry polishers, the continual line systems are computerized and use abrasive bricks. These larger systems may have up to 25 polishing heads, each operated by its own electric motor. The heads and their motors may all be mounted on a single bar and move back and forth across the slabs simultaneously, or they may operate independently. Later models of continual line polishers are equipped with a "sensing bar" which electronically evaluates the dimensions of each slab as it enters the polishing system and relays this information to the individual polishing units. The grit sizes of the grinding heads vary from one end of the polishing line to the other. When the polished slabs emerge from the system, a spray washer is automatically activated and the clean slabs are blown dry to lessen the possibility that residual grit will scratch the mirror-like surface.

In a manually-operated system, the slab is placed flat in a large wooden box called a "bed" which is lined with heavy sheet metal to repel the water and abrasive during the polishing process. The operator manually guides a heavy revolving "scroll" wheel over the slab as abrasives and water smooth and hone the surface of the stone. The scroll wheel is removed and another steel circular emery ring wheel is attached.

Three different grades of emery abrasives are used. Large grains of silicon carbide are first used; then follows a medium grain, and the last grain is very fine, giving the slab a smooth honed finish. An experienced polisher will know when the granite has reached the stage where he will remove the emery wheel and attach a heavy buffing wheel which has thousands of tiny compressed felt pads inserted between steel rings. These soft pads are coated with a mixture of water and tin or aluminum oxide powder, and slowly guided over the entire slab until a brilliant mirror-like polish has been accomplished. From the time the scroll wheel was first attached, to the final application of the buffing wheel and powder takes about 45 minutes.

Shaping a Monument

The slabs then move via bridge crane or roller conveyor to the Breakout Department. Shop tickets specifying the sizes and shapes of an individual monument are taped to the large slab and the breakout man uses chalk to line off the slab to conform with the monument sizes required by the shop tickets.

The slabs are then split into the smaller sizes by a huge stone splitter called a guillotine. The machine has top and bottom rows of carbide-tipped chisel-like teeth on which hydraulic pressure is applied to cleanly and evenly split a slab up to 20-in. thick. The operator uses a hydraulic turntable on the infeed conveyor to position the slab so that its chalk size markings align with the guillotine teeth. He mashes a button and the machine exerts pressure up to 1800 lbs. per sq. in. on the chisel-like teeth which make a crunching sound as they press into the granite prior to the loud bang when the slab finally splits.

The smaller pieces may then be taken to a diamond shaping saws where the monument shaping process continues as edges are saws or cutouts, checks, or notches are created in the stone. These units then move to the Stonecutting Department where some of the Granite Industry's most skilled craftsmen use a variety of hand-held and air-powered, carbide-tipped, chisel-like pitching tools to craft the granite into a monument the exact size and shape specified on the shop ticket. The stonecutter uses a special pencil to line off the granite pieces to the specific monument size. His hammer strikes the pitching tool and pieces spawl off as he shapes the monument to the previously applied monument dimension line.

The shaped unit then moves to a profile grinding machine which grinds the top or ends to conform to a given shape. This machine traverses across a wooden pattern or "profile" of the monument shape, which may be straight, oval, serpentine, concave or some other configuration.

After the top and ends are shaped, the monument moves to the Top and End Polishing Department where a mirror-like polish is applied to the top and/or ends by small polishing heads.

The Sandblast Engraving Process

The monument then goes to the Engraving Department where the fascinating artistic process of carving symbols and letters in granite is accomplished. First, liquid glue is applied to the surface so that a sheet of rubber-like stencil will bond to the granite securely. While the glue dries, the stencil is carefully spread then pressed onto the polished surfaces. In the meantime, a draftsman has been preparing a pattern or "layout" of the exact size and contour of the monument. He has used a thin tracing paper in making this "full size detail" which will contain the family name, inscriptions, floral or other design. Metal letters of proportioned sizes have been selected form the variety of lettering styles available. As the paper is rubbed with a flat object, the carbon will imprint the letters on the backside. The draftsman now layouts the carved floral design. This requires an artistic talent for he must be exact in every minute detail in getting the correct size leaves and flowers or other ornamentation in proportion to the size memorial to be carved.

The full-sized layout is placed over the rubber stencil, the carbon backing is rubbed and transfers the carving and lettering to the stencil. Next, a rubber cutter guides his razor sharp knife along the tiny lines made by the carbon reproduction. As each line is cut, the stencil is pulled from the surface and discarded leaving the sections of granite underneath exposed to the sandblast abrasive.

As in the sawing and polishing processes, computerized technology is also now being used in the monument engraving process and is expected to revolutionize certain phases. The computer-assisted-design (CAD) system is already on line at several companies and more are on the way.

Instead of a draftsperson free-hand drawing or using a press to make a full-size layout for transfer onto stencil, a computer operator simply "calls up" a specific design from a programmed selection. The operator may then use the system's memory banks to select a wide range of lettering styles to be placed on the design. The machine then either makes a full-size layout; or, the tracing pencil may be replaced by a knife-like stylus which cuts out the carving and lettering on stencil mounted on the computer. This "sandblast-ready" stencil is taken directly from the computer and glued onto the surface of the granite monument to be engraved.

The monument is next moved to the metal sandblast room..powerful lights insure that the operator has a perfect view of each line. The operator stands outside the room, his hands protected by heavy rubber gloves. He holds the large rubber air hose inserted into a 4-in. long, tapered ceramic nozzle through which abrasive exits under 100 pounds of air pressure. The operator sprays abrasive evenly into each exposed area of the granite while the uncut stencil portions reflect and protect the polished surface. Through his years of experience, the sandblast operator knows when the correct depth has been achieved to bring out the contrast and beauty of the letters and the shape-carved flower designs.

When this has been completed, the monument is moved by overhead crane and deposited on the wash rack. Live steam removes the remaining glue and tiny particles of stencil. A soft fiber brush is used for the final cleaning. The monument dries thoroughly and is carefully wrapped in heavy paper or plastic to protect the highly polished surface from scratches while enroute to its destination. Heavy wooden crates are built to fit the monument tightly to prevent it being chipped or damaged when delivered to the retail monument dealer who has placed the order for this beautiful Elberton Granite memorial which will mark the final resting place of a loved one . . .

1 There is no date on this publication, although I received my copy in 1997.



[Top of Page]