Principles of tubular free abrasive drilling

Олег Кругляков

February 2018–June 2018

Tubular free abrasive drilling is a drilling technique in which abrasive particles are trapped and transported in the hole being drilled by the inner and the outer surfaces of a tube made of soft metal or metal alloy.

Translated by Dmitrij Kazak

Copper and tubes

Figure 2 — Copper statue of King Pepi I

It is assumed that copper melted from the ore was poured onto a stone surface. After cooling down, the obtained “pancakes” were hammered with stone hammers to the necessary thickness, annealed in order to eliminate the strain hardening, cut to sheets of the necessary size, and were likely stored in this form until needed. It is a widely known fact that Ancient Egyptians were masters in working with sheet metal. Furthermore, copper is a perfect material for raising, dishing, and other types of tinsmithing works. Examples from the 20^th century are diving bell helmets hammered out of copper sheets. Examples from the time of the Old Kingdom are copper bushings, fittings of a bed canopy from the tomb of Hetepheres (a Queen of Egypt and the mother of King Khufu), and elaborate and finely made hollow statues of King Pepi I.

“The twenty-five different pieces of which the canopy is composed were joined by tenons and sockets in which the tenons fitted. These parts were all cased in copper to form practical bearing surfaces.” (Reisner, George A. “The Bed Canopy of the Mother of Cheops.” Bulletin of the Museum of Fine Arts, Boston 30, no. 180 (August 1932), pp. 56–60.)

Figure 1 — Copper fittings of the canopy of Queen Hetepheres’s bed

The canopy is constructed of a whole grove of wooden poles encased in tubes rolled from a metal sheet.

“The ten tent-pole supports (columns) around the sides were of especially heavy gold. The shaft was a tube made by rolling a single sheet into cylindrical form and welding the edges together.” (Ibid.)

It should be mentioned that a split tube is much more efficient in drilling than a solid one. Why? We will discuss this later. Meanwhile, let’s just say that there is no need to cut the latter in order to make the former: a split tube can be made by wrapping a metal sheet around a wooden bar.

Abrasives

The abrasive used with a tube made of soft metal (copper) shall be a suspension of mineral particles in water, and the particles shall be at least as hard as the hardest component of the material intended for drilling. For a long time it has been thought by geologists that the hardest loose abrasive available in Egypt is desert sand, which to a large extent consists of quartz particles (Mohs hardness 7).

But the shape of the grooves in some drill holes suggests that the abrasive used for drilling was harder and coarser than sand: edges of grooves are ragged and the surface in general is considerably rough (Figure 3). Experiments show that sand suspension makes groove edges and the inner surface of a drill hole smoother.

And this suspicion has been confirmed: recently, a fragment of stone with traces of drilling has been found in Amarna.

The bottom of these drill holes were covered with a dried-out greenish pulp – a mixture of particles of abrasive, ground stone, and oxidized copper from a tube. The abrasive component consisted of corundum grains (Mohs hardness 9) a large deposit of which has been revealed at Wadi Hafafit.

Drive

A copper tube was fixed to the bottom end of a wooden axle which was rotated as part of a bow drill. This method was used by ancient Egyptians only for drilling very small holes with a diameter of perhaps 1–2 cm (Figure 3).

Figure 3 — A bow drill in an ancient Egyptian image

For drilling holes of larger diameters, braces with inertial weights were used. A brace with a rigidly fixed weight, i.e. a flywheel (Figure 4), is much more convenient in operation: as far as our experiments show (Figure 5), in this case the weight does not loosen, and if you have mastered the technique of it and the abrasive suspension is prepared properly, the only thing you need is to maintain inertial rotation with one hand. The position of the tool relative to the stone workpiece is then stabilized by the gyroscopic effect.

Drill hole cross-section

An inevitable consequence of drilling with loose abrasive is that the cut narrows from top to bottom. The situation when the copper tube first wobbles irregularly (creating a wider hole to begin with) is then stabilized and the cross-section of the drill hole soon takes the shape of a cut channel. To achieve two perfectly parallel walls would require the use of a hard-alloy drill bit with teeth. Its inner and outer surfaces behind the cutting edge are smooth and, therefore, cannot broaden the drill hole after it has been drilled.

Drilling with abrasive suspension is a different process altogether, as the rotation of the brace and the tubular drill bit is precessional. While wobbling, the tube shakes the pulp in the drill hole from top to bottom both inside and outside itself, and friction of the pulp against the surfaces of the drill hole and the core not onlyslows down the rotation of the tube but also makes the drill hole broader at the top. The core, consequently, widens to the bottom.

Figure 6. Walls of the drill hole (left) and the core (right). The cut width at the bottom is about 1 mm

Metamorphosis of the cutting edge

Figure 7 — Stages of sharpening of the tube cutting edge and the result

The cutting edge of the tube, originally blunt, rubs abrasive particles together and compacts them to the inside and outside, where they start beveling its end (Figure 7). When all grains are squeezed from under the tube end, they continue to sharpen it from both sides, while it touches the bottom of the cut and grinds it.

The profile of the cut becomes V-shaped. Experiments show that a sharpened tube rotates easier, but if the cutting edge becomes too thin and sharp, it gradually flares outwards under the axial load (Figure 8).

Figure 8. Tube surface with caverns left by corundum grains. The cutting edge is flared outwards.

Grains of loose abrasive intrude into the soft surface of the copper tube for a short time and act as fixed file teeth of great hardness. It is in fact with these “teeth” that the tube drills the stone. Little caverns left on the surface of the tube by abrasive particles show (Figure 8) how firmly these particles intrude into copper.

Grooves

The mechanics of groove formation on the inner surface of a drill hole is related neither to the drilling process itself (when abrasive grains embed themselves into the copper near the cutting edge of the tube) nor to the rhythmic character of feeding the abrasive into the working area. The key observation is that after replacing the abrasive suspension with dry or wet abrasive, or even with the suspension with a high concentration of abrasive, these grooves disappear within 2–3 minutes, and the surfaces of the drill hole and the core become smooth. If, however, we again add to the suspension with the proper concentration of abrasive, grooves will return in several minutes.

When not agitated, the suspension separates and abrasive particles settle to the bottom of the drill hole under their own weight. The grooves start to appear on the surface above the tube cutting edge as the suspension is shaken and stirred by the rotating tube, which presses and rubs them against the drill hole wall and the core surface (Figure 9).After a grain has scratched a groove, the nearest grains start slipping into it and fill it, therefore, the nearest groove can then only be scratched to a certain point.

Figure 9. Profile of a drill hole wall / core surface with grooves

Figure 10. Grooves scratched by splashing suspension on the wall of a wooden stencil, initially smooth, The stencil was laid onto the granite workpiece to make the start of drilling more convenient

Figure 11 — Abrasive grains in scratched
grooves, a schematic diagram

If there are not too many abrasive grains within the suspension being pressed by the tube to granite surfaces, they rather quickly slip from crests into the nearest grooves. That is why the distances between grooves are more or less equal (Figure 12).

Figure 12 — A granite core from a modern drill experiment

There is one more mechanism for groove formation and deepening. Due to surface tension, at the moment when the tube unsticks from the drill hole wall / core surface, the pulp is sucked into local areas of momentarily decreased pressure in the form of blobs, separated due to viscosity. These blobs are spread over granite surfaces by the tube in the direction of its rotation and fill the grooves scratched by separate abrasive grains deepening and broadening them.

Tubes: solid vs. split

Figures 13 and 14 show the results of abrasive drilling of a granite block and a porcelain tile with a solid tube.

Figure 13. A granite block drilled with a solid tube
Figure 14. A porcelain tile drilled with a solid tube

The abrasive suspension fed into the drill hole from outside of the tube leaked inside it only through a narrow gap, which was opening under the cutting edge due to tube tilting. Therefore, only a small amount of pulp was between the tube and the core. As a result, circular grooves are clearly seen on the drill hole wall but are almost invisible on the core surface. Of course, they do not have any practical value in either case, but it is important that the abrasive works only outside the solid tube which makes drilling half as efficient. Truly efficient drilling requires an optimal amount of pulp both inside and outside the tube. This is ensured by a split tube, or to be more exact, rolled from a copper sheet wrapped around a bar. Such a tube has a longitudinal opening, which ensures free circulation of pulp through its wall inside and out. Circular grooves of the core are a side effect in this case.

Cores

Figure 15. Petrie’s Core#7

Among frequent archaeological finds are granite cores knocked out from drill holes as waste material. Here is a picture of the much-talked-about core found by Sir William Matthew Flinders Petrie with his own description below:

“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.” (The pyramids and temples of Gizeh. by: Petrie, W. M. Flinders (William Matthew Flinders), Sir, 1853-1942. Publication date: 1883. p. 75.)

The Industrial Revolution at the end of the Victorian era had influenced people’s minds, including those of Petrie…

Of course, Petrie’s Core#7 does not bear any regular helices or a thread cut in granite with a fixed jewel point with a pitch of 2.0 mm, as it has been described by him. There is only a series of grooves, the formation mechanism of which is described above in detail. Their pitch, being very irregular, is not related to the advance movement of the tool cutting edge.

Figure 16 — Petrie’s Core 7G (left) and a core from the modern experiment (right). The point where several grooves converge (four on the left image and two on the right one), are shown by the arrows. It is also seen that grooves cross fields of feldspar (pink fields) and quartz and mica (dark fields) with equal ease.

Some grooves randomly jump from line to line, and this can give the appearance of a helix—but only to an inexperienced eye. Nevertheless, how can abrasive grains cut quartz, feldspar, and biotite evenly to one and the same depth? The tube wall is hard enough that it does not react to local changes of hardness of the granite surfaces inside the drill hole. Pressing abrasive grains against the granite surface, it neither protrudes nor creases when it shifts from a harder spot to a softer one and back.

In ancient Egypt

When holes drilled in granite blocks at doors or gates were used as hubs for hinge pins, their inner walls were smoothed—perhaps, prior to actual usage. This was done in order to remove grooves from granite surfaces and, thus, to protect hinge pins against excessive shearing. See Figures 17 and 18.

Figure 17 — Smoothed walls of drill holes used as hinge hubs, Saqqara, Egypt. The right view shows green traces of oxidized copper-and-abrasive pulp.

Figure 18 — Profile of a smoothed wall of a drill hole

Figure 19 — Karnak, Egypt. Supposedly, the 18th dynasty. A hinge hub, diameter about 18 cm. The wide and deep additional groove at the hole outlet was made for fixing a copper bushing—a kind of friction bearing. The right picture shows the profile of the bottom cut

Holes in heavy objects were drilled for using as lifting lugs. For instance, four holes were drilled in the lid of the sarcophagus of Akhethotep (a high dignitary and probably a son-in-law of King Khufu, the 4^th dynasty) to lift, transport, and install into its place. A good example of a slanted lifting hole is in the lid of the granite sarcophagus from the mastaba of prince Kawab (the eldest son of King Khufu). The bent shape of the hole is a mere deception caused by the shape of the chip.

Figure 20 — Sarcophagi of Akhethotep and prince Kawab, Old Kingdom

Tubular abrasive drilling could also be an initial step in making stone vessels. Then, if required, the drill hole could be lathed or widened in some other way.

Often, non-cylindrical hollows were also made by tubular drilling. For this purpose, holes were drilled close to each other—either with or without overlaps. (Figures 21 and 22). But the obtained cores were not knocked out immediately. Until the work was complete, they were kept in their initial positions in order to fix the copper tube from sides during each drilling cycle. Also, cores left in place took up a certain volume thus making it possible to use only a moderate amount of abrasive suspension. The level of suspension was kept constant.

Figure 21 — Cavities made by drilling multiple holes, ancient Egypt
Figure 22 — Overlapping drill holes, experiment results, 2016

The same method was used for making sarcophagi. Traces of abrasive drilling are still preserved on some of their inner surfaces because it was difficult to remove them from hard stone. Sometimes, hubs for hinge pins of large gate doors were also made in this way—by drilling several smaller holes instead of a single large hole.

Figure 23 — A hub in the second pylon of the Mortuary Temple of Ramesses III at Medinet Habu, Luxor, Egypt

Experiments of Nikolay Vasyutin

2010. Drilling with a quasi-split tube

Materials: granite, corundum (a cutting disc crushed to sand), and a split tube. A low-speed drill was used as a drive. The universal joint (Figure 24) between the drill chuck and the tube was inserted in order to imitate free wobbling of a drill bit of a hand brace.

The split copper tube used in this experiment could hardly be called “split” and even “a tube”. It was made of a rolled up copper sheet and the distance between the edges of the side opening was about 18 mm (Figure 25). This opening ensured free circulation of abrasive suspension in a drill hole between the inner and the outer volumes. Appearance of grooves on the core and the drill hole wall ( Figures 28–30) also caused by this opening. Abrasive suspension was fed into the space between the hole wall and the tube without removing the latter.

Figure 24 — Universal joint between the drill chuck and the tube
Figure 25 — The width of the opening in the tube wall after the experiment

The split copper tube used in this experiment could hardly be called “split” and even “a tube”. It was made of a rolled up copper sheet and the distance between the edges of the side opening was about 18 mm (Figure 25). This opening ensured free circulation of abrasive suspension in a drill hole between the inner and the outer volumes. Appearance of grooves on the core and the drill hole wall ( Figures 28–30) also caused by this opening. Abrasive suspension was fed into the space between the hole wall and the tube without removing the latter.

Figure 26 — The copper tube after the experiment

Figure 27 — Side surfaces of the core and the drill hole after the experiment

Figure 28 — Core surface, development view

Figure 29 — Core surface profile

2016. Drilling with a quasi-split tube

Materials: granite, corundum (a cutting disc crushed to sand), and a solid (quasi-split) copper tube. A hand-made brace was used as a drive. Its plaster flywheel ensured vertical load and gyroscopic effect for drill bit stabilization. The drill bit itself was a solid copper tube approximately 2 mm thick. To ensure circulation of abrasive suspension, several through-holes of 10 mm diameter were drilled in the tube body instead of a longitudinal cut in a split tube.

Figure 30 — A hand brace with a copper tube on wooden axle

This experiment went wrong from the very beginning. Firstly, the selected abrasive material was too coarse and its grains started to tearthe granite surface, dislodging individual crystals. Secondly, the abrasive suspension was oversaturated for most of the experiment. It was not taken into account that, being once fed into the process area, a portion of abrasive could not be consumed completely — its volume was only reduced a little due to mutual grinding of grains. It was not the same as with granite sawing when the suspension was constantly spilling out of a cut back and forth and needed to be replenished in large amounts. So, lacking experience, we continually poured suspension into the gap between the hole wall and the tube making the pulp ever thicker. Each time a new portion of abrasive was added to the pulp (corundum, granite, copper) when the previous portion had not yet been abraded. The drilling process was accompanied by a dry scraping noise although the granite block being drilled was put into a bucket full of water. By the end of the work, when the tube sank into the cut to approximately 5 cm, it was very hard to rotate the brace: there was so much abrasive that it filled the whole space between the tube and the walls from both sides. The result is shown in Figure 31.

Figure 31 — The core, the inner surface of the drill hole and the cut profile

The inner surface of the drill hole bears some rough and almost erased circular grooves, while on the core surface they are practically invisible. This is because there was now an opening in the tube body large enough for pulp circulation: small round holes were a poor substitution for a longitudinal cut. Also, there was no vertical splashing of suspension against the core surface.

Figure 32 — The copper tube at the very beginning and after the experiment

Figure 33 — The result of drilling with a quasi-split tube

The tube was often taken out to check the cut depth. But before it was set back into its place, a thick layer of pulp had already settled to the bottom of the cut. Therefore, the tube edge, already sharpened, got slightly blunted again while cutting to the bottom through the pulp layer. Nevertheless, it was sharpened gradually, though not so quickly as if it had not been removed and set back now and then.

Some data on these two experiments (#4, 2010 and #6, 2016) of Nikolay Vasyutin are given in Table 1.

Table 1 — Experimental data

Experience #

Tube diameter, mm

Abrasive type

Core diameter, top / bottom,

mm

Drilling diameter, top / bottom, mm

Drilling depth, mm

Tube wear, mm

Vertical load, kg

Rotational speed, rpm

Drilling speed, mm/hour

4

46,5(2)

corundum

39,4/43

50,5/50

70

20

4

100-150

8-12

6

47,6(2)

corundum

39,8/44

50,6/47

50

15

11

approx. 150

approx.10

May 2017. Drilling with a quasi-split tube

Materials: granite, corundum (a cutting disc crushed to sand), and a solid (quasi-split) copper tube. This was a successful attempt to document the skill of applying corundum abrasive optimally. The brace and the tube were the same as the year before. Then the task was to shoot a video for the first time ever demonstrating techniques used for drilling hard stone with primitive tools. The experiment was a success in the sense that an ancient hand brace was reconstructed and that drilling granite with a copper tube and abrasive was proved to be possible. But still, it failed in the sense that “truly ancient Egyptian grooves” were erased soon after emerging.

Still, the main task was to figure out the working conditions that ensured this particular pattern of holes. The physics and mechanics of how grooves appeared in granite had been understood long ago—many hinge hubs in granite lintels from ancient Egypt bare such grooves—but details of the process remained unknown and unclear. We should understand how ancient workers actually operated. For this purpose Nikolay Vasyutin had conducted more than 20 experiments before the conditions of granite grooving became clear and the repeatability of such results was obtainable.

In this experiment, in 2017, the abrasive was fed under the close supervision of Nikolay, who took it on himself to rotate the brace. Making “truly Egyptian” grooves came easily to him, while precession of the brace axle in inexperienced hands could have damaged them even if the abrasive had been fed correctly.

The moment when the corundum abrasive should be replenished was identified by the processing sound — a quiet hissing. A portion of abrasive was put on the flattened tip of a knitting needle directly into the gap between the tube and the drill hole wall. At that moment the processing sound changed from hissing to scraping, which continued for around a minute or two. The noise then turned to hissing again, and this signified that it was time to add a new portion. The correct amount—a 4–5 mm lump of wet corundum—was found by trial and error: it should provide easy rotation and efficient drilling without blocking the processing area or erasing grooves.

Figure 34 — An assistant puts a portion of abrasive on a needle tip into the processing area between the tube and the drill hole wall

Another method that was tried was to heap the abrasive near the cut—inside the plasticine collar plastered around it—and flick the correct portion into the processing area at the right moment (at the changing of the processing sound) or flush it with a thin trickle of water.

The tube — the same one as in the previous experiment—was fixed to the axle in a more authentic way: with wooden wedges and a rough cord. The tube edge continued self-sharpening and in total has sharpened from 1.8 to 0.3 mm.

Figure 35 — Experiment results

Figure 36 — Bow drilling in ancient Egypt.

May 2017. Bow drilling

Let’s return to the beginning, i.e. to bow drilling with the use of copper tubes. It seems that this method was used by the ancient Egyptians only for drilling holes of smaller diameters, as in this case less effort was required.

The work with a brace clearly showed what force should be applied to overcome friction in gaps. It also became clear that the process was energized mostly by the rotating flywheel while the operator’s hand only maintains this rotation supplying some additional energy to the flywheel. Besides, the tube position against the block was stabilized by the gyroscopic effect that ensured roundness of the future drill hole. In comparison, the work with the bow drill was fraught with considerable difficulties that demonstrated the difference between these two tools. Though, as experiments showed, those difficulties could be overcome.

For this experiment we used a split tube with a diameter of approximately 16 mm —almost three times smaller than in the experiment with the inertial brace.

Figure 37. A split tube lock seam on the pole of a bow drill

Pole diameter and tube inner diameter ~ 15 mm;

Total tool length (from the tube working edge to the pole tip) 615 mm;

Width of the longitudinal cut 5.0 mm;

Thickness of the copper sheet 0.6 mm.

Figure 38. A bow drill with a tubular drill bit.

If the arm of force, i.e. drill pole radius, is small, the torque is also small. Besides, the force of the bow string applied to such a short arm presses the tube to the nearest side of the hole and to the far side of the core. If drilling in this mode for a considerable time, the obtained hole will be oval—as well as the core with its shorter axis aligned with the direction of string movement (Figures 39 and 40).

Figure 39 —The result of the first experiment with bow drilling

Figure 40 — The shape and dimensions of the hole and the core

Dimensions of the hole and the core:

А = 10.6 mm;

B = 13 mm;

C = 20.5 mm;

D = 18.3 mm;

Maximum drilling depth = 13mm.

Such a result was unacceptable. The answer was to increase the radius of the pole at the point where the string was wound around it. Figure 41 shows a pulley fit onto the pole to increase the radius of application of string tension force. Here the arm of force is elongated and the torque that overcomes resistance in the processing areas is thus increased.

Figure 41 — The bow drill with a pulley

The force that presses the tube to the nearest side of the hole wall and to the farside of the core decreases because with the elongation of the arm of force its point of application shifts aside from the shaft axis.

As it has been supposed, this tool is only useful for drilling small holes. If the drill bit diameter—not the shaft diameter—is small, it takes less effort to rotate the drill. Besides, in this case the shaft does not librate considerably: being jerked by the string, it is rather rotating than librating. The speed of drill rotation is lower but the precision of drilling is higher: the tube is not pressed to the drill hole surfaces in the way illustrated in Figures 39 and 40 and, thus, the ovality of the drill hole and the core decreases noticeably (Figures 42 and 43).

Figure 42 — The result of drilling with a tube of a small diameter
Figure 43 — The same drill hole with the core taken out

In the next stage, the shaft was shortened almost up to the pulley and this made drilling even more convenient. In the next experiment, a flat river cobble was drilled through with a lock-seamed solid copper tube (Figure 37 above) in less than 5 minutes.

Figure 44 — Bow drilling of a river cobble of unknown type (possibly limestone), May 14, 2017

Figure 45 —The edge of a solid copper tube before (left) and after drilling (right). The sharpening effect is obvious

Figure 46. The result of granite drilling with a bow drill with a solid tube of a small diameter. Abrasive material: corundum (a cutting disc crushed to sand)

May 2018. Large diameter drilling

The following experiment was conducted in order to test a method of drilling large diameter holes similar to hinge hubs in temple pylons. Essentially, this drilling method should be the same as those described above. But the aim was to check whether it was at all possible to turn a 20-cm tube by hand while overcoming the resistance of the abrasive material.

A 0.6 mm thick copper sheet was wrapped around one end of a log of 19.5 cm in diameter and nailed to it with five copper nails. A gap of approximately 1 cm was left between the strip ends for free circulation of the abrasive pulp (Figure 47). Before the start, the copper sheet and the workpiece were weighed. This workpiece was a granite tile of approx. 25×25×2.5 cm (Figure 48). In addition, a wooden supporting structure was specially built for fixing the brace, i.e. the log (Figures 49 and 50).

Figure 47 — A log wrapped with a coppersheet for the experiment
Figure 48 — A granite tile before drilling

Figure 49 — The wooden supporting structure built for brace fixing
Figure 50 — The brace fixed inside the wooden supporting structure
Figure 51 —Just a working shot
Figure 52 —The copper “drill bit” in a wooden stencil

Surprisingly enough, drilling itself didn’t take much effort (Figure 53). The abrasive was again fed based on the telltale processing sounds: when it changed from a scraping to hissing noise, a small portion of corundum was flushed by a trickle of water from the wooden stencil into the processing area (Figures 52 and 54).

Figure 53 —Rotating the brace.
Figure 54 — The copper “drill bit” in a wooden stencil, a detailed view

Taking turns, the four of us worked for four hours and then checked the interim result (Figure 55). The brace was lifted, the workpiece was taken from underneath and flushed. The result turned out to be long known and expected: a slightly tapered profile of the drill hole with a rounded bottom of the cut.

Figure 55 — The granite tile half-drilled
Figure 56 — The cut widening at the top

At the top, the cut was wide enough (4 mm) because the wooden stencil hadn’t completely prevented the copper tube from wobbling from side to side (Figures 56 and 57).

Figure 57 — The cut width

The tool was then reassembled — this time without the wooden stencil as the depth of the cut was sufficient to hold the tube firmly (Figures 58 and 59).

Figure 58 — The tube in the cut without the stencil.
Figure 59 — The tube in the cut without the stencil, a detailed view.

The next day we worked for about five hours. At a certain moment, the water suddenly drained out from the cut—an arc of around one third the diameter of the circle was sawed through. This happened because the tile thickness was not uniform: 23 to 27 mm.

The workpiece was washed of pulp but in the process of knocking the core out it cracked in two halves (Figure 61). The cutting edge of the tube was predictably covered with small caverns left by abrasive particles (Figure 62).Walls of the core and the drill hole had also been covered with grooves—somewhat erased by the excess of abrasive material (Figure 63).

Figure 60 — The granite tile drilled through and cracked
Figure 61 — Small caverns on the cutting edge
Figure 62 — Grooves on drilled surfaces are slightly erased

The profile of the bottom cut on both sides also looks quite characteristic and predictable (Figure 63).

Figure 63 — The bottom cut profile

Figure 64 below shows cone angles of V-shaped bottom cuts. On the left picture, there is a well-known find—the hinge hub drilled in a granite lintel located near to the sixth pylon in the Hall of Annals of Thutmose III at Karnak. The right picture illustrates the result of our experiment.

Figure 64 — V-shaped bottom cuts in the ancient (left) and the modern (right) granite samples

After the experiment, the granite and copper materials were once again weighed and measured. The obtained values are the following:

Copper tube thickness: 0.6 mm

Granite tile thickness: 23 to 27 mm

Circular cut diameter: 195 mm

Max. drilling depth: 23 mm

Max. width of the cut at the top: 4 mm

Cone angle of the cut at the bottom: ~9°

Corner radius of the cut at the bottom: ~0.5 m

Total time: 9 hours

Granite wear: 4128–4038=90 g / 33.3 cm³

Copper wear: 366–315=51 g / 5.7 cm³

Copper to granite mass wear ratio: 51/90 g or 1/1.8

Copper to granite volume wear ratio: 5.7/33.3 cm³ or 1/5.8

The last experiment

One more experiment, interesting for us to conduct, was drilling with a tube home-cast with true copper ore. So, we needed a thin cast and forged plate that should be then annealed and rolled into a tube with a large diameter. Unfortunately, what was ordered and delivered to us turned out to be a ready-made cast tube with thick walls and with almost the same diameter as was used in previous experiments (Figure 65).

Figure 65 — A solid home-cast copper tube

This would reveal nothing new or interesting: the drilling process would be very inconvenient due to excessive thickness of the tube walls and no circulation of the abrasive as the tube was solid. Also, the cut width in this case would be enormous—as well as the time needed for grinding the corresponding amount of granite into pulp. For that reason, it was decided to drill the softest workpiece to hand—the same as was used in previous experiments with bow drilling.

Figure 66 — Drilling with a brace

Figure 67 — The home-cast tube after drilling

By the end of the experiment the tube had expectedly sharpened and was covered with small caverns left by brief intrusions of abrasive grains. But its inspection from inside showed that drilling had been performed in semi-idle mode: the inner surface of the tube remained practically intact as the pulp had been soaking inside only at its occasional tilts (Figure 67).

The abrasive had been fed irregularly this time.

The results of this final series of experiments are shown in Figures 68 and 69.

Figure 68 — The workpiece drilled through with the home-cast tube

Conclusion

To show the exact methods of stone processing that were really in use in the ancient Egypt was not the aim of our experiments. Rather, ours was an engineering approach: we started from the investigation and identification of traces left by ancient tools.

In the course of our experiments, we examined practical techniques of working with such tools in order to understand what they could have been in ancient times.

From the technical point of view, the tools were simple enough and the task was to clarify the details of their use. Then, if those techniques were reproduced correctly, traces on test workpieces should be exactly the same as those seen in ancient materials. Thus, our aim was to understand the principles of hard stone working.

***

Figure 70 — The results of the final experiments

The photo-shots and pictures – O.Kruglyakov, N.Vasyutin, V.Androsov and from the opened sources in an internet.

***

Select Bibliography

Petrie, W. M. Flinders, On the Mechanilal Methods of the Ancient Egyptians, 1883
Petrie, W. M. Flinders, Tools and Weapons Illustrated by the Egyptian Collection in University College, London (London: 1917)
Denys A. Stocks, Experiments in Egyptian Archaeology: Stoneworking Technology in Ancient Egypt (Routlege, 2003)
Anna Serotta. Evidence for the use of corundum abrasive in Egypt from the Great Aten Temple at Amarna
Somers Clarke, Reginald Engelbach, Ancient Egyptian Construction and Architecture, Dover Publications, New York 1990
Lucas, A. 1962. Ancient Egyptian Materials and Industries. 4th edn, revised J.R. Harris. London, Edward Arnold and Mineola (NY)
Reisner, George A, Reisner, George A., "The Bed Canopy of the Mother of Cheops," BMFA 30.180 (August 1932)