The Giza Power Plant Page 11
FIGURE 18. Tube-drilling a Granite Box
The errors Petrie noted are not uncommon in modern machine shops, and I must confess to having made them myself on occasion. Several factors could be involved in creating this condition, although I cannot visualize any one of them being a hand operation. Once again, while working their drill into the granite, the machinists had made a mistake before they had time to correct it.
Let us speculate for a moment that the drill was being worked by hand. How far into the granite would the Egyptian craftspeople have been able to cut before the drill had to be removed to permit cleaning the waste out of the hole? Would they be able to drill eight or nine inches into the granite without having to remove their drill? It is inconceivable to me that they could have achieved such a depth with a hand-operated drill without the frequent withdrawal of the drill to clean out the hole or without their making provisions for the removal of the waste while the drill was still cutting. By frequently withdrawing the drill, however, they would have been able to expose their error and notice the direction their drill was taking before it had cut a .200-inchgouge into the side of the coffer and before it had reached a depth of eight or nine inches. The same situation applies as easily with the drill as with the saw—a high-speed operation made an error before the operators had time to correct it.
Although the ancient Egyptians are not given credit for having the wheel, the fact is that archaeological evidence, when evaluated with a machinist's eye, proves that they not only had the wheel, but they used it in very sophisticated ways. The evidence of lathe work is markedly distinct on some of the artifacts housed in the Cairo Museum, as well as those that were studied by Petrie. And if the Egyptians indeed used a lathe, then they had developed the wheel, for the products turned on a lathe, being circular, have the elements of being wheels—in fact, the wheels that are used on locomotives are turned on lathes. So although the lathes used by the ancient Eygptians have long disappeared, Petrie was very clear that they had existed when he identified the marks of true lathe turning on two pieces of diorite in his collection. It is true that intricate objects can be created without the aid of machinery simply by rubbing the material with an abrasive such as sand or using a piece of bone or wood to apply pressure. The relics Petrie was looking at, however, in his words, "could not be produced by any grinding or rubbing process which pressed on the surface."6
FIGURE 19. Petrie's Bowl Shards
The simple rock bowl shards Petrie was studying would hardly be considered remarkable to the inexperienced eye. However, Petrie, devoting as much care to the observation of this artifact (a) as he did to others, found that the spherical concave radius forming the dish had an unusual feel to it. Upon closer examination, he detected a sharp cusp where two radii intersected, indicating that the radii were cut on two separate axes of rotation (see Figure 19).
I have witnessed the same condition when a component has been removed from a lathe and then worked on again without being recentered properly. On examining other pieces from Giza, Petrie found another bowl shard that had the marks of true lathe turning (b). This time, though, instead of shifting the workpiece's axis of rotation, a second radius was cut by shifting the pivot point of the tool. With this radius, they machined just short of the perimeter of the dish, leaving a small lip. Again, a sharp cusp defined the intersection of the two radii.
While browsing through the Cairo Museum, I found evidence of lathe turning on a large scale. A sarcophagus lid had distinct lathe turning marks. The radius of the lid terminated with a blend radius at shoulders on both ends. The tool marks near these corner radii were the same as those I have observed when turning an object with an intermittent cut. The tool is deflected under pressure from the cut, and then relaxes when the section of cut is finished. When the workpiece comes round again to the tool, the initial pressure causes the tool to dig in. As the cut progresses, the amount of "dig in" is diminished. On the sarcophagus lid in the Cairo Museum, tool marks indicating these conditions were exactly where one would expect to find them (see Figure 20).
Egyptian artifacts representing tubular drilling are clearly the most astounding and conclusive evidence yet presented to indicate the extent to which machining knowledge and technology were practiced in prehistory. The ancient pyramid builders used a technique for drilling holes that is commonly known as "trepanning." This technique leaves a central core and is an efficient means of hole making. When making holes that did not go all the way through the material, the workers drilled to the desired depth and then broke the core out of the hole. Trepanning was evident not only in the holes that Petrie studied, but on the cores cast aside by the masons who had done the work. Regarding tool marks that left a spiral groove on a core taken out of a hole drilled into a piece of granite, Petrie wrote, "On the granite core, No.7, the spiral of the cut sinks .1 inch in the circumference of 6 inches, or 1 in 60, a rate of ploughing out of the quartz and feldspar which is astonishing."7 After reading this, I had to agree with Petrie. This was an incredible feedrate (distance traveled per revolution of the drill) for drilling into any material, let alone granite. I was completely confounded as to how a drill could achieve this feedrate. Petrie was so astounded by these artifacts that he attempted to explain them at three different points in one chapter of his book.8 To an engineer in the 1880s, what Petrie was looking at was an anomaly. The characteristics of the holes, the cores that came out of them, and the tool marks would be an impossibility according to any conventional theory of ancient Egyptian craftsmanship, even with the technology available in Petrie's day. Three distinct characteristics of the hole and core, as illustrated in Figure 21, make the artifacts extremely remarkable:
FIGURE 20. Sarcophagus Lid in the Cairo Museum
A taper on both the hole and the core.
A symmetrical helical groove following these tapers showing that the drill advanced into the granite at a feedrate of .10 inch per revolution of the drill.
The confounding fact that the spiral groove cut deeper through the quartz than through the softer feldspar.
In conventional machining the reverse would be the case. In 1983 Donald Rahn of Rahn Granite Surface Plate Co. told me that diamond drills, rotating at nine hundred revolutions per minute, penetrate granite at the rate of one inch in five minutes. In 1996, Eric Leither of Tru-Stone Corp. told me that these parameters have not changed since then. The feedrate of modern drills, therefore, calculates to be .0002 inch per revolution, indicating that the ancient Egyptians drilled into granite with a feedrate that was five hundred times greater or deeper per revolution of the drill than modern drills! The other characteristics of the artifacts also pose a problem for modern drills. Somehow the Egyptians made a tapered hole with a spiral groove that was cut deeper through the harder constituent of the granite. If conventional machining methods cannot answer just one of these questions, how do we answer all three?
For those who may still believe in the "official" chronology of the historical development of metals, identifying copper as the metal the ancient Egyptians used for cutting granite is like saying that aluminum could be cut using a chisel fashioned out of butter. What follows is a more feasible and logical method, and it provides an answer to the question of techniques the ancient Egyptians may have used in all aspects of their work.
FIGURE 21. Petrie's Valley Temple Core & Hole
The fact that the feedrate evenly spirals along the length of the granite cores is quite remarkable considering the proposed method of cutting. The taper indicates an increase in the cutting surface area of the drill as it cut deeper, hence an increase in the resistance. A uniform feed under those conditions, using manpower, would be impossible. Petrie's theory of a ton or two of pressure being applied to a tubular drill consisting of bronze inset with jewels does not take into consideration that under several thousand pounds of pressure the jewels would undoubtedly work their way into the softer substance (the bronze), leaving the granite relatively unscathed after the attack. Nor does
this method explain the groove being deeper through the quartz.
It should be noted that Petrie did not identify the means by which he inspected the core, whether he used metrology instruments, a microscope, or the naked eye. It also should be noted that Egyptologists do not universally accept his conclusions. In Ancient Egyptian Materials and Industries, A. Lucas takes issue with Petrie's conclusion that the grooves were the result of fixed jewel points. He wrote:
In my opinion, to suppose the knowledge of cutting these gem stones to form teeth and of setting them in the metal in such a manner that they would bear the strain of hard use, and to do this at the early period assigned to them, would present greater difficulties than those explained by the assumption of their employment. But were there indeed teeth such as postulated by Petrie? The evidence to prove their presence is as follows.
(a) A cylindrical core of granite grooved round and round by a graving point, the grooves being continuous and forming a spiral, with in one part a single groove that may be traced five rotations round the core.
(b) Part of a drill hole in diorite with seventeen equidistant grooves due to the successive rotation of the same cutting point.
(c) Another piece of diorite with a series of grooves ploughed out to a depth of over one-hundredth of an inch at a single cut.
(d) Other pieces of diorite showing the regular equidistant grooves of a saw.
(e) Two pieces of diorite bowls with hieroglyphs incised with a very free-cutting point and neither scraped nor ground out.
But if an abrasive powder had been used with soft copper saws and drills, it is highly probable that pieces of the abrasive would have been forced into the metal, where they might have remained for some time, and any such accidental and temporary teeth would have produced the same effect as intentional and permanent ones. . . .9
Lucas went on to speculate that the workers withdrew the tube-drill in order to remove waste and insert fresh grit into the hole, thereby creating the grooves. However, there are problems with this theory. It is doubtful that a simple tool that is being turned by hand would remain turning while the artisans draw it out of the hole. Likewise, placing the tool back into a clean hole with fresh grit would not require that the tool rotate until it was at the workface. There also is the question of the taper on both the hole and the core. Both would effectively provide clearance between the tool and the granite, thereby making sufficient contact to create the grooves impossible under these conditions.
In contrast, ultrasonic drilling fully explains how the holes and cores found in the Valley Temple at Giza could have been cut, and it is capable of creating all the details that Petrie and I puzzled over. Unfortunately for Petrie, ultrasonic drilling was unknown at the time he made his studies, so it is not surprising that he could not find satisfactory answers to his queries. In my opinion, the application of ultrasonic machining is the only method that completely satisfies logic, from a technical viewpoint, and explains all noted phenomena.
Ultrasonic machining is the oscillatory motion of a tool that chips away material, like a jackhammer chipping away at a piece of concrete pavement, except much faster and not as measurable in its reciprocation. The ultrasonic tool bit, vibrating at 19,000-to 25,000-cycles-per-second (hertz), has found unique application in the precision machining of odd-shaped holes in hard, brittle material such as hardened steels, carbides, ceramics, and semiconductors. An abrasive slurry or paste is used to accelerate the cutting action.10
The most significant detail of the drilled holes and cores studied by Petrie was that the groove was cut deeper through the quartz than through the feldspar. Quartz crystals are employed in the production of ultrasonic sound and, conversely, are responsive to the influence of vibration in the ultrasonic ranges and can be induced to vibrate at high frequency. When machining granite using ultrasonics, the harder material (quartz) would not necessarily offer more resistance, as it would during conventional machining practices. An ultrasonically vibrating tool bit would find numerous sympathetic partners, while cutting through granite, embedded right in the granite itself. Instead of resisting the cutting action, the quartz would be induced to respond and vibrate in sympathy with the high-frequency waves and amplify the abrasive action as the tool cut through it.
The tapering sides of the hole and the core are perfectly normal when we consider the basic requirement for all types of cutting tools. This requirement is that clearance be provided between the tool's nonmachining surfaces and the workpiece. Instead of having a straight tube, therefore, we would have a tube with a wall thickness that gradually became thinner along its length. The outside diameter becomes gradually smaller, creating clearance between the tool and the hole, and the inside diameter becomes larger, creating clearance between the tool and the central core. This would allow a free flow of abrasive slurry to reach the cutting area. By using a tube-drill of this design, the tapering of the sides of the hole and the core is explained. Typically this type of tube-drill is made of softer material than the abrasive, and the cutting edge would gradually wear away. The dimensions of the hole, therefore, would correspond to the dimensions of the tool at the cutting edge. As the tool became worn, the hole and the core would reflect this wear in the form of a taper (see Figure 22).
The requirement for advancing an ultrasonic tool into a workpiece is for the cutting edge of the tool to apply pressure to the workpiece as the vibratory motion of the tool does the actual cutting. This can be accomplished two ways: The tool can plunge straight down, or it can be screwed into the workpiece. We can explain the spiral groove if we select the latter method as the most likely one used. It should be made clear that the rotational speed of the drill is not a major factor in this cutting method; it is merely a means to advance the drill and apply pressure to the workpiece. Using a screw-and-nut method, the tube-drill could be efficiently advanced into the workpiece by turning it in a clockwise direction (see Figure 22). The screw would gradually thread through the nut, forcing the oscillating drill into the granite. It would be the ultrasonically induced motion of the drill that would do the cutting, not the drill-bit's rotation. The latter would be needed only to sustain a cutting action at the workface. By definition, the process is not a drilling process by conventional standards, but a grinding process in which abrasives are caused to impact the material in such a way that a controlled amount of material is removed.
The fact that there is a groove at all in the Valley Temple core may be explained several ways. An uneven flow of energy may have caused the tool to oscillate more on one side than the other, the tool may have been improperly mounted, or a buildup of abrasive on one side of the tool may have cut the groove as the tool spiraled into the granite.
FIGURE 22. Ultrasonic Drilling of Granite
Another method by which the grooves could have been created was through the use of a spinning trepanning tool that had been mounted off-center to its rotational axis. Clyde Treadwell of Sonic Mill Inc. explained to me that when an off-centered drill rotated into the granite, it would gradually be forced into alignment with the rotational axis of the drilling machine's axis. The grooves, he claimed, could be created as the drill was rapidly withdrawn from the hole.
If Treadwell's theory is the correct one, it still requires a level of technology that is far more developed and sophisticated than what the ancient pyramid builders are given credit for. This method may be a valid alternative to the theory of ultrasonic machining, even though ultrasonics resolves all the unanswered questions where other theories have fallen short. When we search for a single method that provides an answer for all the data, we find that neither primitive nor most conventional machining methods provide that answer; consequently, we are forced to consider methods that are cutting-edge technologies even in our own time.
It goes without saying that further studies need to be made. One way to decide between opposing theories is to replicate the cores using the advanced machining methods I propose and the more primitive methods proposed by so
me Egyptologists. Following such a replication, the cores can be compared using metrology equipment and a scanning electron microscope in order to detect the microscopic changes in the structure of the granite that can result from the pressure and heat exerted or created by the tool. I doubt many Egyptologists share my conclusions regarding the pyramid builders' drilling methods, so it would be beneficial to perform these tests in order to prove conclusively the most likely method the builders used for cutting stone.
As this book was being prepared for publication, I received an unexpected e-mail from NOVA's stonemason, Roger Hopkins, who had read my article about ancient Egyptian technology on the Internet. He wrote: