Waterjetting 35b - Cutting the Missouri Stonehenge video

The video that I posted last time did not fare as well as had been hoped, in making the trip from my computer to the blogger post, and so this week, to see if there are other ways of peeling the apple, I have also posted a copy of the video to Youtube, to see if this works better.

The video is of the making of the Missouri Stonehenge for which, as I have mentioned in a previous post, we used a jet pressure of around 15,000 psi with a flow rate of 10 gpm.

The video makes the point that a high-pressure jet system can, with relatively little support, cut a straight edge down the side of a block, even if there is only a very thin layer of rock to remove. It is normally very difficult to do this with a conventional cutting saw, or similar tool, which requires more material on the free side to stop the blade from being deflected away from the cut line.

If this new posting works as I hope, then I will be posting a number of different videos that have been collected over the years, but on Youtube initially, though I will provide the link as I have above.

Waterjetting 15a - Carving a Stonehenge

This post is a marriage of two different themes that have recently appeared at Bit Tooth. The first, under the Waterjetting title, has contained a discussion of the different aspects of high-pressure waterjet use. The second, more recent theme discussed both the original Stonehenge and then how the MS&T Stonehenge, which is a working calendar, functions. In this post I am going to talk about how the MS&T megalith was built, and since it involves the use of high-pressure water it seems appropriate to include it in the Waterjetting Series.

As I have noted in one of the earliest waterjetting posts we had learned, from Russian literature, back in 1966 that waterjets could be used to cut into granite. From results of an unplanned test, we had learned that the pressures needed to cut through granite need not be that high. Others had predicted that it would take a jet pressure of up to 30-times the rock compressive strength in order to penetrate rock efficiently. However both the Russians and ourselves had been able to drill through a 30,000 psi granite with a waterjet pressure of only around 10,000 psi, rather than the predicted 900,000 psi.

We had done this by moving the jet over the surface so that, as the jet passed across the cracks between grains, so it would penetrate and pressurize the crack, causing it to grow and remove the grain, without having enough pressure to cut through the grain itself.

Figure 1. 9-inch thick block of granite drilled through by a 10,000 psi waterjet at Leeds University. It took over 30 minutes. (Summers, D.A., Disintegration of Rock by High Pressure Jets, Ph.D. Thesis, Mining Engineering, University of Leeds, U.K., 1968.)

We had drilled this block of rock back in Leeds and the nozzle was pointing vertically downwards, as we rotated the rock beneath it. After drilling a shallow central hole, we stepped the nozzle out a short distance and repeated the process, breaking the outer ring of rock to the central core. Then after widening the hole, we could come back to the center and advance the nozzle into the rock, and repeat the process. Because of the nozzle size we had to continually step the hole to a smaller diameter as the hole got deeper, and thus there is a rapid taper to the walls.

Moving forward to the early 1980’s when Chancellor Marchello asked Dr. Marian Mazurkiewicz and I to cut the rock for his Stonehenge, and we knew that we could cut the rock at a pressure below 15,000 psi (the size of the pump that we had at the time). But tests where we had made multiple passes over a rock had shown that, with a direct vertical cut to an edge, that repeated passes would taper the cut inward over time – naturally doing what we had done artificially at Leeds.

Figure 2. Early tests on granite cutting. Note that the lower cut was made with two jets diverging at about 5 degrees, and the one above it with the jets diverging at 11 degrees. (The nozzle was spinning and moved across the face of the rock several times).


These tests showed that we needed a higher angle to ensure that the sides did not taper, and while this could be achieved with the nozzles angled at 15 degrees to the perpendicular, because the jets had to cut a path wide enough for the nozzle to enter the slot, an angle of 45 degrees was used after a short series of experiments.

Our team at the Rock Mechanics and Explosives Research Center (RMERC) had been asked to carve the rock, since we had just prior to the commission, been down in Georgia demonstrating to the granite industry there that waterjets were able to economically cut granite.

Figure 3. Starting to cut a 1-inch wide slot in granite, pressure 14,000 psi, 90 rpm, linear cutting speed around 9 ft/min, areal cutting rate around 20 sq. ft./hour.( Raether, R.J., Robison, R.G., Summers, D.A., "Use of High Pressure Water Jets for Cutting Granite," 2nd US Water Jet Conference, Rolla, MO., April, 1983, pp. 203 - 209.)

Concurrently with showing that this could be economic we had also shown that the technique removed the respirable dust from the air that is generated with a flame-torch cut, and that the noise level would drop to industrially acceptable levels from the “jet engine roar” of a cutting torch.

Figure 4 Showing the flame at the bottom of the burner spalling its way through the granite.

Figure 5. Cutting granite with a flame-jet lance, Graniteville MO 1979. (Note the cloud of very fine particles of granite being blown out of the right side of the slot).

The first thing to do in arranging to cut several hundred tons of granite was to find a source of supply. Unfortunately, at that time the granite quarries in the South-East part of Missouri were closed and other sites in the state did not prove practical. But because we had done the work with the Elberton Granite Association in Georgia, we were able to arrange to purchase rock from one of the Quarries around Elberton, Ga. They themselves had recently constructed their own version of the standing stones, the Georgia Guidestones although these had been cut to shape using flame jets, rather than water.

Figure 6. The Georgia Guidestones, Elberton GA.

The granite blocks were roughly split to shape in the quarry, and then shipped to Rolla by train. The first block was sent by truck and this proved the benefits of rail, although the size of the cars limited the scale of the monument to half that of the original in the UK. Which meant that the blocks – over 11 ft tall – were one-eighth the weight of the originals.

Figure 7. Blocks of granite in the cutting frame. The cutting lance is the thin rod in the center of the picture.

The blocks were brought to the RMERC and placed in position using a crane. Dr. Mazurkiewicz and his students had built this frame from wooden blocks, with the guide rails made from radio antenna mast. The lance moved on a cross-beam, also made from radio antenna mast. The low reaction force from the jets meant that the forces on the structure were very small. Thus the head itself could be pulled along the track using a bicycle chain, and small, fractional horse-power motors could be used to move the head and advance it into the slot. Although, by that time, self-rotating heads had been developed, it was decided that a better control of the cut edges could be achieved if the head was hydraulically rotated.

Figure 8. Detail of the cutting platform. The two hoses feed a hydraulic motor that gear-drives the rotation of the cutting lance. The high-pressure water feeds through the hose to a small swivel at the top of the lance. A small electric-motor driven screw behind the platform elevates and lowers it on the guide rails to advance the nozzle into the cut.

In order to keep the slot width as narrow as possible the nozzle holder was made as small as the feed pipe, with the two jets issuing from small carbide inserts within the holder.

Figure 9. Detail showing the nozzle holder and a nozzle orifice on the lance.

Experiments showed that an effective cutting rate of around 20-square feet an hour (depending on the direction of cut relative to the planes of the granite) could be achieved. The lance was rotated at 90 rpm, and moved down the cut at a speed of 9-ft per minute. The two jets, at a pressure of around 14,000 psi (there was some pressure loss in the system) would cut into the rock around 1/3rd of an inch on each pass, and the lance would be lowered this amount after the pass, and then the direction reversed and the jets would cut back along the rock. (This is somewhat faster than the hand-held stone flattening of the original Stonehenge rocks in England, although studies in Peru, where a similar technique was used to shape to blocks that build Machu Picchu showed that it is possible to flatten about 1 square foot an hour once you learn how to chip the rock). Professor Parker Pearson has also noted that the UK original had the rocks finally shaped after they had been erected).

Figure 10. Showing the jet arrangement, raised after a side had been trimmed so that the jets could be seen. Normally with the jet in the cut there is little to show the cutting action.

It took about a morning to cut one side of a block (or in later stages to cut one of the large blocks in half for the smaller stones). Once the second side had been cut, the block was turned and the rail aligned to cut the third and fourth sides. Overall, given that the operations had to be shut down during the winter where the temperatures were below freezing, the blocks were cut and completed over the course of two semesters, largely working with undergraduate student labor.

After the blocks were cut, they were taken to the site, where each was placed in position using a crane. Because of the precision required to align the blocks with the sun, this was a time-consuming operation. The major standing stones were then held in place with an additional pour of 18-inches of cement. (They stood on a cement platform).

Figure 11. Lowering a block into place.

The monument was dedicated at the Mid-summer solstice in 1984, with John Bevan, a Druid of the Gorsedd performed the dedication.

Figure 12. Speakers at the Dedication: Dr. Joe Senne – who designed the megalith; John Bevan – Druid; Dr. John Carlson – from the Center for Archaeoastronomy; Dr. Joseph Marcello – Chancellor.

The construction was sufficiently novel that it was awarded one of the ten Engineering Awards from the Society of Professional Engineers.

(Note there is a video of the construction available on DVD. This shows, in part, that the jets can trim an edge without any material on one side, something other tools find difficult, because the nozzle does not contact the rock). There are also other articles that I have written answering some questions and describing the site on the RMERC web page.)

Waterjetting 1d - Not quite that simple!

When I first began the research on the applications of high-pressure water that was be one of the major parts of my professional life I must confess to a certain naïve innocence in regard to other folk’s work. One assumed that other folk had made similar mistakes to mine, and then corrected them, so that when different systems were compared that the early, obvious, mistakes had not been made.

One of the first times I found that this wasn’t the case was when we were asked to go and demonstrate that high-pressure waterjets could economically cut granite, in quarries located in the heart of the Granite industry, in Elberton, Georgia. We were working with Georgia Institute of Technology (Georgia Tech) at the time and were asked if we could, at very short notice, go down to a couple of quarries and run a demonstration.

Back during my graduate studies I had found that Russian claims were true that said that it was possible, with a 10,000 psi jet pressure to cut through a rock with a compressive strength of 30,000 psi. (I'll tell you how later)

Figure 1. 9-inch thick block of granite drilled through by a 10,000 psi waterjet at Leeds University. It took over 30 minutes. (Summers, D.A., Disintegration of Rock by High Pressure Jets, Ph.D. Thesis, Mining Engineering, University of Leeds, U.K., 1968.)

Knowing this, and having a suitable pump at Rolla, our group ran some tests at the RMERC to get the angles right between the two jets that we were to use, and then, about a week later, we went down to Elberton and set up a system in the quarry.

Figure 2. Starting to cut a 1-inch wide slot in granite, pressure 14,000 psi, 90 rpm, linear cutting speed around 9 ft/min, areal cutting rate around 20 sq. ft./hour.( Raether, R.J., Robison, R.G., Summers, D.A., "Use of High Pressure Water Jets for Cutting Granite," 2nd US Water Jet Conference, Rolla, MO., April, 1983, pp. 203 - 209.)

The trials demonstrated that high-pressure water could cut granite at commercial rates, we cut a slot some 11 ft long and about 2-ft deep, and, after a couple of days of work, we went home. Georgia Tech then went to one of our competitors who set up to run a similar test. We had been done in 2 days, it took them two weeks to cut a slot about 2 ft long and 6-ft deep. They were running a jet system at 45,000 psi, roughly 3 times the pressure of our system. Why did they do so badly?

Well it turned out that they connected their pumps to the nozzle through a very narrow length of high-pressure tubing, and we calculated (as later did they) that of the 45,000 psi being supplied at the pump, some 35,000 psi had been lost in overcoming friction between the pump and the nozzle, As a result they were trying to cut the granite with jets at a pressure of 10,000 psi effective pressure, and it was much slower than our system which retained most of the 14,000 psi from the pump to the nozzle. (Hilaris, J.A., Bortz, S.A., "Quarrying Granite and Marble using High Pressure Water Jet," paper D3, 5th International Symposium on Jet Cutting Technology, Hanover, FRG, June, 1980, pp. 229 - 236.)

Now you may note that I said something about mistakes – it turns out that we had made an identical mistake a few years earlier and had added a second 10-ft length of narrow diameter tubing to the nozzle, and suddenly a system that had cut adequately with 10-ft of tubing did not work with 20-ft. The reason was the pressure loss in the tubing was too great at the longer length, and the pressure fell below that required to cut into the rock. (But at the shorter length we were drilling the hard sandstone at 12-ft/minute).

It is a very simple mistake, and many folk have made it over the years. The system has to be designed from one end to the other to ensure that all the parts are properly sized for the systems that are to be used. (And I will refer to other cases such as that above as we go through this series.)

It is not just the diameter of the feed lines that is important. In 1972 it took, on average, 150 man-hours and about $2,000 for the U.S. Navy to clean a single ship boiler using chemicals and mechanical scrubbing and cleaning. An enterprising company showed the Navy that it was possible to use waterjet lances to clean the tubes. In the demonstration they cleaned a boiler in 10 hours, and it cost around $700. This being Government work, the Navy then arranged a competition to find the most effective contractor. Based on the performance of the system that had been used in the first demonstration they asked 5 companies to compete in cleaning boilers. The operating equipment was designated as having to operate at 20 gpm, at a pressure of 10,000 psi. The results were not even close, even with systems nominally the same.

Figure 3. Relative cleaning efficiency in areal percentage cleaned, of five competing systems in cleaning heat exchanger tubes in Navy boilers. (Tursi, T.P. Jr., & Deleece, R.J. Jr, (1975) Development of Very High Pressure Waterjet for Cleaning Naval Boiler Tubes, Naval Ship Engineering Center, Philadelphia Division, Philadelphia, PA., 1975, pp. 18.)

One of the differences between the competing systems, you won’t be surprised to hear, was that some had smaller feed hoses than others.

There are many different reasons that the various systems performed as they did. One of the aims of this series is to ensure that, should you be asked to engage in such a competition, you will know enough to follow the path of company A, rather than company E.

As systems have become more sophisticated the different factors that control the performance of the jets have increased in number. As a simple example, when abrasive particles are mixed with high-pressure water in streams of abrasive-laden waterjets at pressures that can run up to 90,000 psi in pressure, for high precision cutting of material, the factors controlling performance now include not only the delivery system for the water, but also that for the abrasive, the type of abrasive and the configuration of the nozzle through which that final cutting jet is created.

Again, when we were asked to compare the performance of these different systems we set up nominally identical test conditions under which to determine which nozzle system would perform better. If I were honest I would tell you that before the tests began I expected that the variation in performance of the systems would vary by perhaps 10% between the best and the worst. We were quite surprised by the result.

Figure 4. Comparative performance between 12 nominally similar abrasive waterjet cutting nozzles in cutting through steel at a standard speed, pump pressure, and abrasive concentration.

I use these last two figures to show that all the details of a high-pressure waterjet system are important, when it comes to optimizing performance. One of the reasons to write this series is to ensure that folk that use these systems in the future do not make the mistakes that we made, as we learned how to tune the systems from getting poor performance to the commercially viable rates that are achieved today.

Unfortunately much of the early research and tests that are the basis for this knowledge were performed before the Internet existed. As a result I will have to use references to books and papers (as above) rather than using the electronic references that are the more common habit now.

This concludes the basic introduction to the series, which will now focus on more specific subjects.