Figure 11.7. Horizontal CNC lathe (Courtesy Danville Metal Stamping)
Figure 11.8. Petrie’s Core 7 G, housed in the Petrie Museum, University College London, UC16036, granite, height 4.33 inches (11 centimeters)
Petrie’s drawing of Core 7 and his thorough description formed the basis of my analysis. Petrie describes it:
On the granite core, broken from a drill hole (No. 7), other features appear, which can only be explained by the use of fixed jewel points. Firstly, the grooves which run around it form a regular spiral, with no more interruption or waviness than is necessarily produced by the variations in the component crystals; this spiral is truly symmetrical with the axis of the core. In one part a groove can be traced, with scarcely an interruption, for a length of four turns. Secondly, the grooves are as deep in the quartz as in the adjacent feldspar, and even rather deeper. If these were in any way produced by loose powder, they would be shallower in the harder substance—quartz; whereas a fixed jewel point would be compelled to plough to the same depth in all the components; and further, inasmuch as the quartz stands out slightly beyond the feldspar (owing to the latter being worn by general rubbing), the groove was left even less in depth on the feldspar than on the quartz. Thus, even if specimens with similarly deep grooves would be produced by a loose powder, the special features of this core would still show that fixed cutting points were the means here employed.
Next the Egyptians adapted their sawing principle into a circular, instead of a rectilinear form, curving the blade round into a tube, which drilled out a circular groove by its rotation; thus, by breaking away the cores left in the middle of such grooves, they were able to hollow out large holes with minimum of labour. These tubular drills vary from ¼ inch to 5 inches in diameter, and from 1/30 to 1/5 thick. The smallest hole yet found in granite is 2 inches diameter, all the lesser holes being in limestone or alabaster, which was probably worked merely with tube and sand. A peculiar feature of these cores is that they are always tapered, and the holes are always enlarged towards the top. In the soft stones cut merely with loose powder, such a result would naturally be produced simply by the dead weight on the drill head, which forced it into the stone, not being truly balanced, and so always pulling the drill over to one side; as it rotates, this would grind off material from the core and the hole. But in the granite core, No. 7, such an explanation is insufficient, since the deep cutting grooves are scored out quite as strongly in the tapered end as elsewhere; and if the taper was merely produced by rubbing of powder, they would have been polished away, and certainly could not be equally deep in quartz as in feldspar. Hence we are driven to the conclusion that auxiliary cutting points were inserted along the side, as well as around the edges of the tube drill; as no granite or diorite cores are known under two inches diameter, there would be no impossibility in setting such stones, working either through a hole in the opposite side of the drill, or by setting a stone in a hole cut through the drill, and leaving it to project both inside and outside the tube. Then a preponderance of the top weight to any side would tilt the drill so as to wear down the groove wider and wider, and thus enable the drill and the dust to be the more easily withdrawn from the groove. The examples of tube drilling on Pl, viii. are as follow:—No. 7, core in granite, found at Gizeh. No. 8, section of cast of a pivot hole in a lintel of the granite temple at Gizeh; here the core being of tough hornblende, could not be entirely broken out, and remains to a length of .8 inch. No. 9, alabaster mortar, broken in course of manufacture, showing the core in place; found at Kom Ahmar (lat. 28° 5'), by Prof. Sayce, who kindly gave it to me to illustrate this subject. No. 10, the smallest core yet known, in alabaster; this I owe to Dr. Grant Bey, who found it with others at Memphis. No. 11, marble eye for inlaying, with two tube-drill holes, one within the other; showing the thickness of the small drills. No. 12, part of the side of a drill-hole in diorite, from Gizeh, remarkable for the depth and regularity of the grooves in it. No. 13, piece of limestone from Gizeh, showing how closely the holes were placed together in removing material by drilling; the angle of junction shows that the groove of one hole just overlapped the groove of another, probably without touching the core of the adjacent hole; thus the minimum of labour was required. The examples of tube drilling on a large scale are the great granite coffers, which were hollowed out by cutting rows of tube drill-holes just meeting, and then breaking out the cores and intermediate pieces; the traces of this work may be seen in the inside of the Great Pyramid coffer, where two drill-holes have been run too deeply into the sides; and on a fragment of a granite coffer with a similar error of work on it, which I picked up at Gizeh. At El Bersheh (lat. 27° 42') there is still a larger example, where a platform of limestone rock has been dressed down, by cutting it away with tube drills about 18 inches diameter; the circular grooves occasionally intersecting, prove that it was done merely to remove the rock.9
The most startling feature of the granite core Petrie describes is the spiral groove around the core indicating a feed rate of 0.100 inch per revolution of the drill. In my article, I stated that this feed rate was five hundred times faster than modern diamond drills, which penetrate at only 0.0002 inch per revolution. This has been incorrectly interpreted by some, who have concluded that a hole of the same dimension could be drilled five hundred times faster by the ancient Egyptians than by modern drills. The correct way to describe the feed rate would be to say it was five hundred times greater than modern diamond drills, but the rotation of the drill would not have been as fast as the modern drill’s nine hundred revolutions per minute.
When I read Petrie’s description of this drill core, I tried to imagine what kind of process could replicate it. It seemed very clear that the spiral groove that wound down the core like a drunken screw (Petrie’s description) could not have been made by any loose grains rubbing on the granite. Petrie notes that the groove cut deeper through the quartz than the feldspar, which in conventional drilling would actually be the reverse, because quartz is the harder material. The taper on the core and the hole were also quite puzzling, because they did not lend to the idea that the groove was cut while a rotating tool was withdrawn from the hole. Yet the action of a tool that reflected a feed rate of 0.100 inch per revolution of the drill was not the work of conventional drilling as we know it and demanded consideration of other processes in its creation. All of these features were considered without the physical examination of the artifact in question and were considered phenomenal not just by me alone, but also by colleagues with whom I discussed their relevance.
It seemed from the evidence described by Petrie that a sure way to create the spiral groove was to use a process whereby the tool oscillated, like a jack hammer or hammer drill, while it turned. I selected the method to be ultrasonic (see figure 11.10), because with quartz having resonant properties, it would respond to the vibration and this might explain the deeper cut through the quartz than the feldspar.
Figure 11.9. Egyptian core drilling hole and Core 7
Figure 11.10. Ultrasonic machining of granite
Figure 11.10 shows a basic concept of how the drill worked. The core drill was attached to an assembly that included a horn assembly and transducer and a threaded shaft (figure 11.10 B). While axially oscillating, the assembly was turned by way of a turn knob (figure 11.10 A) through a nut assembly (figure 11.10 C).
This idea, of course, while popular in some circles, was certainly not popular among Egyptologists, one of whom is Denys Stocks, who writes, “Despite this apparent abundance of evidence, many people still argue that these simple tools were not capable of producing the artifacts that survive and, therefore, that there had to be some as yet undiscovered technology that the Egyptians possessed. These supposed technologies include diamond-tipped saws and drills and even the use of sonic waves to cut stone.”10
Stocks goes on to claim in his article that he had been able to replicate and demonstrate the efficiencies of the tools we “know” were in the ancient Egyptians’ tool
box. His work is exhaustive and goes to great length in describing every step of his methods, and it includes photographs of bow drills, copper chisels, stone axes, and copper tubes for grinding into diorite using sand as well as an example of a small urn being drilled.
With such a comprehensive and complete study of how simple, primitive tools were applied in prehistory, and with the support of academia behind him, it would seem that the subject of ancient technology was an open-and-shut case. Yet because we have already examined two theories on ancient saws and found them lacking, Stocks’s efforts to prove how the ancient Egyptians drilled granite using core drills must be examined more closely.
Mike Brass, a South African Egyptology student, first advised me of Stocks’s effort to drill granite using a copper tube and sand. I must admit I did not take it seriously, as it conflicted with Petrie’s assertions based on his observations of the core in his possession, and the idea was counter to my own personal experience and knowledge of the capabilities of drills. Therefore, I did not refer to it when my article was reprinted. I probably should have given it more attention, for it is the simplest method devised because it demands the introduction of the least number of unproven assertions. The materials are already in the archaeological record, and pictorial images can be interpreted as ancient Egyptians using those materials in their working of stone. The experiments by Stocks are lodged firmly in the academic record and are referenced by Deiter Arnold in Building in Egypt.11 This should be enough, we might think, to accept those findings and look no further for answers.
Yet there is that nagging question spiraling around Core 7 in the Petrie Museum. Stocks described the results of a drilling experiment that was conducted in 1999 as part of his involvement with the Lehner/ Hopkins Nova obelisk experiment. Regarding a core that he ground out of granite using quartz sand and a copper tube attached to a shaft and manually driven by a bow and sand, he writes, “Horizontal striations similar to the ancient ones on rose granite were visible both in the wall of the hole . . . and upon the core.”12, 13
Stocks’s seemingly innocuous statement actually speaks to the heart of the debate regarding the technology used by the ancient Egyptians to drill granite. Horizontal striations, as opposed to helical grooves, would sink the sonic machining theory in a sea of vibrating quartz quicksand, where it will forever rest and, perhaps, be remembered by some as an interesting yet troublesome theory and by others as the product of an overactive imagination. When we look at Core 7 and the drunken crawl of the groove around its circumference, there seems to be a lack of order and certainty to them. Is it possible that Petrie was mistaken or confused when he described this core? Lucas and Harris were not convinced that his evidence supports his conclusion that jewel teeth were set in bronze saws and tubes to create these grooves, but they did not question his observations that the groove was spiral and not horizontal. In Ancient Egyptian Materials and Industries, they write:
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 advanced to prove their presence is as follows:*3
(a) A cylindrical core of granite grooved round and round by a graving point, the grooves being continuous and forming a spiral, within 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.14
Petrie’s observations of a helical groove were explained by Stocks to be the result of the random action of quartz sand in the drilling process. This process produces, for the most part, horizontal striations, which he noted in his drilling experiment.15
Other experiments were made by Leonard Gorelick and A. John Gwinnet of the School of Dental Medicine S.U.N.Y at Stonybrook, who show the results of drilling using a copper tube and emery grit, a component of which is magnetite and corundum. Corundum has a hardness of Mohs 9. Gorelick and Gwinnet claimed that by using emery, they were successful in grinding out concentric grooves in glass, but indicated that quartz sand would not perform as well.16
Seeking to resolve the question of helical versus horizontal grooves, two men set about verifying them by examining the central piece of evidence that was located in the Petrie Museum. John Reid, an acoustics engineer who is noted for his work on pyramid acoustics, and Harry Brownlee, an expert stonemason and sculptor, concluded after their inspection of Petrie’s Core 7 that the grooves were horizontal, not helical, as described by Petrie.
In their book Giza the Truth, Ian Lawton and Chris Ogilvie-Herald write:
They [Reid and Brownlee] make the critical distinction, not effectively made by Dunn, between the horizontal striations that are found on all cores—these being separate grooves, which are on close inspection randomly spaced—and spiral striations, which are genuinely connected spiral grooves. Petrie reports that he found these latter on only one piece, which he examined—our old friend drill core ‘No. 7’, whereon he described four connected spiral turns. Reid and Brownlee have examined and photographed this core in minute detail, and report that even on this they can detect only horizontal striations [see plate 26]; they can only conclude that there may be some confusion in the labeling of the artifact at the musem.17
While Lawton and Ogilvie-Herald stress that Petrie found the spiral striations on only one piece, this is not true. As Lucas and Harris state, other examples were found and noted by Petrie: “Another piece is part of a drill hole in diorite. This has been part of a hole 4½" in diameter, or 14" circumference as the seventeen equidistant grooves appear to be due to successive rotations of the same cutting point, we have here a single cut 20 feet in length.”18
Thanks to the publication of Lawton’s and Ogilvie-Herald’s book, I now had knowledge of where Core 7 was housed and went to London to examine it myself. I had taken Petrie’s word on his observations of a spiral groove and had made assertions based on his observations. Because of the controversial nature of my theory, and the questions raised by Lawton and Ogilvie-Herald, I suspended those assertions subject to my own observations. It should not have been a surprise to me that not only would I be criticized heavily for my theory of ultrasonic drilling, but also that Petrie’s critical observations, which I used to support my conclusions, would also be questioned and ultimately rejected, for if they were to stand as observed by Petrie, then the theory that ancient drill holes were cut using copper and sand would be difficult, if not impossible, to substantiate.
It is noteworthy that Reid and Brownlee are confident in describing horizontal striations. On a truncated cone such as Core 7, it requires more than visual inspection to determine if a groove with a slight pitch, or distance between the start and end point in a 360° turn, is helical or horizontal. Petrie provided dimensions in his analysis, while neither Stocks nor Reid nor Brownlee nor Lawton nor Ogilvie-Herald have produced any measurements to support their assertion that Petrie’s observations were incorrect—only that they “had examined the core in minute detail.”19 Petrie, on the other hand, following his lecture to the Royal Anthropological Institute on April 24, 1883, in which he received comments from several attendees who proposed that his findings were more likely to have been produced using abrasives such as emery powder or corundum, provided a footnote for his article that appeared in the RAI’s Journal the following year. The footnote provided a further analysis he had made of
the core in which he took specific measurements of the groove at 90° angles around its 360° circumference four times.
In consequence of remarks on the granite core I have examined it more carefully. It offers apparently a complete proof that the lines were cut by fixed points, and not by rubbing of a loose powder; for the grooves are cut as deeply in the quartz as in the feldspar. And the feldspar being somewhat rubbed down, by general friction, the lines are actually cut through a greater thickness in the harder quartz which stand above the feldspar. Now no loose power could cut down to exactly the same depth in material of different hardness like quartz and feldspar; still less would it cut more out of the prominent quartz; but a fixed point must cut to the same depth in each material.
Lost Technologies of Ancient Egypt: Advanced Engineering in the Temples of the Pharaohs Page 27