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On Site with Ditch Witch's All Terrain Drill

Published in: Construction Equipment
Date: 1/1/2001

Two days of drilling rock in Texas allow a close look at how the new JT2720 All Terrain performs against its popular predecessor

Ditch Witch's design goal for its new JT2720 All Terrain horizontal directional drill was clear-cut: Create a small machine capable of effectively boring and steering in a broad range of soil types. And since introducing the new model last October, the company has not been at all shy about promoting the performance and potential of this 20,000-pound machine, a weight that includes 325 onboard feet of its new "shaft-within-a-pipe" drill rod.

The All Terrain's patented new drilling system uses this special pipe, says Ditch Witch, to effectively handle conditions as varied as solid rock, cobble, caliche, gravel, clay and just plain dirt. When drilling in rock, says the company, the JT2720 All Terrain works more productively than considerably heavier machines using conventional, single-pipe drill strings to drive rock bits.

Against comparable mud-motor systems, according to Ditch Witch, the JT2720 All Terrain delivers equal performance on reasonably long shots, but uses just a small fraction of the drilling fluid required by the mud motor. Plus, says Richard Levings, product manager for the Ditch Witch trenchless line, a mud-motor system would require fluid-reclamation, which would add considerable cost to the overall drilling system.

Levings admits that these are, indeed, strong claims, but says they are based on the company's evaluation of the JT2720 All Terrain during its five-year development. He cautions, though, that the All Terrain is not a wonder machine. Anytime you build a drill to take on a great diversity of ground conditions, compromises are involved, both in the basic design of the machine and in the choice of down-hole tools and drilling fluid. If contractors are to be successful with the new machine, he says, they must be savvy enough to make intelligent decisions about tools and fluid.

But that said, Levings doesn't back away from the basic claim that the JT2720 All Terrain, properly applied, can bore through a variety materials that otherwise might require the use of a heavier machine or a mud-motor system. The new machine, he says, can relieve the contractor of having to repeatedly retract the drill string and change bits as conditions in a rocky bore change. The concept behind the All Terrain, says Levings, is to put one head on the machine, then drill through all the conditions in the bore path.

Evaluating the All-Terrain

Construction Equipment editors haven't seen the new JT2720 All Terrain work against a larger conventional drill, nor against a comparable mud-motor system. We did, however, get the chance to compare the new drill's performance with that of its predecessor, the Ditch Witch RS8/60, during a two-day, late-October visit to a Texas job site. The two drills were installing fiber-optic conduit through extremely rocky soil under driveways and parking lots along Route 183 in the town of Lampasas, about 60 miles northwest of Austin, Texas.

Since its introduction in 1995, the RS8/60 ("RS" for "rock system") has, itself, earned a solid reputation among users as a good rock drill. Given that, we thought it logical to use the RS8/60's onsite performance as a benchmark to evaluate the realworld performance of the new All Terrain.

The JT2720 All Terrain on the Lampasas job was a brandnew, Ditch Witch-owned production machine on loan for evaluation to B. Fair Contracting. Through a series of subcontracting arrangements, B. Fair's owner, Byron Fair, who headquarters his company in Blame, Wash., won a contract for nearly 250,000 feet of horizontal directional drilling along the 370-mile fiber-optics job running from Midland to Temple. In turn, Fair subcontracted a portion of the drilling to Wiebe's Trenching, based in Morden, Manitoba. The RS8/60 on the Lampasas site belonged to Wiebe.

(Fair estimates that about 80,000 feet of the drilling is in rock, and another 150,000 feet in caliche. Caliche can be a stony deposit of sodium nitrate or a crust of calcium carbonate that forms on the stony soil of arid regions. In either instance, it's tough material to drill in.)

Basically, during the two-day comparison, CE editors kept numbers on Wiebe's RS8/60 the first day, and on B. Fair's JT2720 All Terrain during day two. But since the machines were working in proximity on both days, we could shift between them for an immediate and direct comparison of performance and features. The proximity of the machines also assured reasonably similar soil conditions, which ranged from solid rock and cobble, to caliche and moderately sticky clay mixed with sand. Bores ranged from 230 to 270 feet.

The performance differences we observed in Lampasas are detailed in the sidebars and comparative charts in our report. But to quickly summarize here, the new JT2720 All Terrain was clearly the more efficient, more productive of the two machines. It's our observation that the All Terrain 's superior performance results from a combination of factors, chief among them being its redesigned rock-drilling system. But complementing that basic design change is the All Terrain's operator friendliness and its relative ease of set-up and tear-down.

Fundamental concepts

The focal point of the new JT2720 All Terrain's design is the refinement of its rock-drilling system. To understand this system, it's helpful to look first at the RS8/60's rock-drilling system, which is a "pipe-within-a-pipe" arrangement that uses a 3-inch-diameter outer pipe to steer the drill string (via a 2-degree bent sub), and a smaller-diameter inner pipe to turn the bit.

The outer pipe is the low-torque member in the RS8/60 system, designed to keep thrust pressure on the bit and to turn and hold the bit in a new steering attitude until it establishes a set. The outer pipe then rotates to maintain the chosen direction of travel. The inner pipe is the high-torque member of the system, driving the bit and providing the rotational force and pulling power when backreaming.

To drive its two pipes, the RS8/60 uses what might be called a dual gear case. A rear drive powers the inner pipe, which passes through a concentric opening in the forward case, which, in turn, drives the outer pipe. To use the machine in dirt, the outerpipe drive can be slid forward, tilted to the side and pinned Out of the way, allowing the rear drive to drill with single-pipe sections.

By contrast, the new JT2720 All Terrain uses a "shaft-within-a-pipe" rock-drilling system. In place of the RS8/60's inner pipe, the new model uses a compact but exceptionally strong hex-shaped rod, which turns inside a 2 3/8-inch-diameter outer pipe. The hex shaft powers the bit, creating what Ditch Witch calls a "mechanical motor." A newly designed, one-piece gear case accommodates two hydraulic motors, which drive concentric spindles for the hex rod and outer pipe.

As the drill string is made up during a bore, the hex-rod sections automatically slide together and lock via a collar arrangement, while the outer pipe threads together in a conventional manner. As the hex shaft drives the bit during the bore, the outer pipe, as on the RS8/60, thrusts the bit forward and steers the drill string, again via a bent sub (2.0 degrees). On the pullback, however, the All Terrain uses its higher-torque outer pipe to do the work, while the inner shaft idles.

Use of the hex shaft, says Levings, provides more integrity in a smaller cross section than the RS8/60's inner pipe, allowing the new machine to use smaller-diameter outer pipe, which gives a boost to drilling efficiency in rock. The use of smaller pipe does mean, however, that the All Terrain must use a smaller "tri-cone" roller bit than its predecessor, 4.75 inches vs. 6.00 inches. On the plus side, though, says Levings, the smaller bit allows a more rapid rate of penetration in rock, and it responds much faster to steering commands.

The smaller pipe also necessitates the use of a slimmer beacon housing, which contains smaller, less powerful and shorter-lived batteries than the RS8/60's larger housing. But in Leving's opinion, seldom will the transmitter's power be an issue.

In addition to these mechanical changes in the All Terrain's rock-drilling system, Ditch Witch took great pains, says Levings, to "optimize" its operating parameters for productivity and reliability. The new machine's inner-spindle torque, for example, is actually considerably lower than that for the RS8160, 800 vs. 1,900 foot-pounds. The All Terrain's inner-spindle speed, however, is much higher, 400 vs. 140 rpm. The R58/60 is limited to 140 rpm, because its 6-inch bit would generate too much heat at a higher speed, possibly causing bearing damage.

The new model also has sizable increases in both its outer-spindle torque and speed, 2,700 vs. 1,400 foot-pounds, and 225 vs. 20 rpm, respectively. These adjustments, says Levings, combined with tweaking the maximum thrust load for "optimal weight on bit", plus adding 40 engine horsepower, have given the JT2720 All Terrain about four times more downhole horsepower than its predecessor. The result, he says, is a machine that both drills and backreams more efficiently than the RS8/60.

Features for reducing fatigue

The bores we observed in Lampasas averaged six hours, and in the seat for those long grinds were Wiebe Trenching's Laurie Jackson on the RS8/60, and B. Fair's Bucky Ball on the JT2720 All Terrain. Both men are experienced, expert operators, but it was our observation that Jackson was working far harder than Ball. Jackson continually was making adjustments to the drill, while Ball more often than not was running the All Terrain in its cruise-control mode, both for drilling and pulling back.

The new model's cruise-control feature allowed Ball, with the touch of a button, to set drilling or pullback parameters (rotational speed and thrust), then remove his hands from the controls. When drilling in cruise control, for example, Ball kept an eye on the inner spindle's rotational-pressure gauge, which he liked to maintain around 1,000 psi. If down-hole conditions caused the pressure to vary, he could make quick manual adjustments with the machine's single-lever controller, which, when touched, disengages the cruise control. He could then push the "resume" button to return to the previously selected speed, or the "set" button to select a new drilling speed.

Of course, if you want an opinion about which machine involves more work, ask Jamie McDaniel, who was handling pipe on the RS8/60. It was our observation that lifting the two-pipe sections from the pipe box (usually positioned on the ground next to the drill) and onto the carriage is about all one person can handle. But after a long day, removing these heavy, wet, gritty pipes during the pullback is (again our opinion) best done by two people. The All Terrain, by contrast, has both an automated pipe loader and an automated thread-greasing system.

When making and breaking pipe, Jackson on the RS8/60 had to deal with two threads, one right-hand, the other left-hand, which might be somewhat confusing to a less-experienced operator. On the All Terrain, however, the inner shaft couples and uncouples itself, and the outer pipe is conventionally threaded.

We noted during the comparison that the All Terrain operator was making and breaking joints roughly twice as fast as the RS8/60 operator. This advantage resulted mostly from the design of the drill string, but was enhanced by the new model's two-speed carriage. At the touch of a button on the control lever, the All Terrain's gear case shuttles back and forth at twice normal speed. Also, when its pipe vises are activated, the new machine automatically stops rotation, shuts off the fluid pump and, when drilling, activates the inner spindle's oscillation feature that helps align the shaft sections.

More design refinement

The new JT2720 All Terrain, compared to its RS8/60 predecessor, incorporates other technical refinements that contribute to its overall efficiency and safety. For example, while both machines use a vise-type breakout system, the All Terrain has much beefier vises and cylinders, and the vises are rotated so the operator can easily see the joints. The vise-type system also allows the All Terrain the flexibility to use smaller-diameter pipe when working in dirt, since the jaw need not be sized to fit over the flat of a pipe joint. (The RS8/60 uses its standard inner pipe for dirt drilling.)

Unlike its predecessor, however, the new model is equipped with an onboard mud pump (with a 47-gpm capacity), which simplifies the required fluid-supply system. Having no on-board pump, the RS8/60 needs to be supported with a remote, high-pressure pumping system, which, Levings estimates, might double the cost of the fluid-supply system.

Another refinement, this one aimed at jobsite safety, is the All Terrain's "Tracker Control" system. This electronic system, which works with the company's Subsite Electronics 750 Tracker, shuts down the machine's thrust and rotation hydraulics when the tracking unit is turned off. Thus, the crew at the bore exit can change tools without being concerned about inadvertent rotation of the drill string. A green light on the drilling unit indicates that the tracker control system is activated.

The new model also has diagnostic capability built into its electronic control system. If a fault occurs in a monitored function, a red lamp on the instrument panel blinks a code that identifies the problem.

Summing up

From the point of view of the drill owner or operator, the new JT2720 is a big step forward from its RS8/60 predecessor, in terms of technical refinement that has practical application at the jobsite.

We'd estimate, for example, that the All Terrain, conservatively, could save at least two hours on every job, simply because it sets up and tears down so quickly. From the operator's point of view, there's no comparison between the two machines, given the All Terrain's automated features that so substantially reduce fatigue. The new model is, however, appreciably louder than its predecessor, largely the result of a much more powerful engine and the subsequent requirement for increased cooling, which includes a larger, faster fan.

On a final point, that of overall costs to support these machines on site, the All Terrain is, by far, the more efficient. Since the new model needs no remote mud-pumping system, no laborer to handle pipe, and no assist machine to deal with heavy set-up components, its cost of deployment is substantially less than for the RS8/60.


* New Model JT2720 AT

* Type Directional drill

* Available Fall 2000

* Replaces RS8/60

Basic Specifications

RS8/60 JT2720 AT

Engine horsepower 85 125

Spindle speed-inner 140 rpm 400 rpm

Spindle speed-outer 20 rpm 225 rpm

Spindle torque-inner 1,900 ft-lb. 800 ft.-lb.

Spindle torque-outer 1,400 2,700 ft. lb.

Thrust force 22,500 lb. 16,500 lb.

Pull-back force 22,000 lb. 27,000 lb.

Bit diameter 6.00 in. 4.75 in.

On-board pump capacity n/a [*] 47 gpm

List price (approximate) [**] $235,000 $240,000

(*.)Not applicable; RS8/60 requires a remote pump

(**.)CE estimated package price

JT2720 All Terrain On-Site Production Potential Increase +33%

JT2720 All Terrain Estimated Down-hole Horsepower Increase +4X

Comparing Set-Up and Tear-Down

When comparing the process of setting up the JT2720 All Terrain and the RS8/60, we timed the machines from engine start on the transport trailer, to bit penetration at the beginning of the bore. The experienced crew from Wiebe's Trenching (Laurie Jackson, Joel Keen and Jamie McDaniel) needed 68 minutes and the assistance of a backhoe to set up the RS8/60. The backhoe was needed to place the machine's large anchoring frame and to place the pipe boxes adjacent to the drill.

When the RS8/60's anchoring frame is on the ground, the drill itself must twice straddle the frame to install its pair of anchors, which must be carried to the site by hand. To auger in the anchors, the drill carriage must be elevated to a vertical position in order to use the pipe motor as a power source. With the anchors in, the drill must be moved a third time to center it over the frame, where it's latched into place. Then, in addition to attaching the fluid-supply hose, an electrical cable also must be attached to give the operator control over the remote-mounted mud pump.

By comparison, the JT2720 All Terrain crew, Byron Fair and Bucky Ball, assisted by Ditch Witch product specialists Damon Webb and Mark Rupp, had the All Terrain ready to drill in just 24 minutes. And most of that time was waiting for the drilling fluid to mix. The All Terrain carries its own self-powered anchors and anchor frame, which can be quickly positioned for either rock or soil stake-down. Since the new machine also carries its own pipe, it's basically ready to drill as soon as the anchors are down. Tearing down the machine is as simple as pulling the anchors.

We saw quite an impressive demonstration of the All Terrain's ease of set-up when, about two pipes into the bore, the machine encountered a buried culvert, not on the plan, that ran too close to the intended drill path. The crew relocated the machine in just nine minutes. Since tear-down time alone on the RS8/60 was timed at 46 minutes, we figure that if the RS8/60 had snagged the culvert, the crew would have needed at least two hours to reposition.

Evaluating Drilling and Pullback Performance

For the bores, the JT2720 All Terrain and the RS8/60 used the same fluid mix, which, for every 500 gallons, consisted of 100 pounds of TRUBORE bentonite (Wyo-Ben Thc.), a cup of VIS-PLUS polymer thickener (Akzo-DreeLand Inc.) and 1.5 cups. of TORQ-LESS clay inhibitor/torque reducer (Sun West Mud Co.). Each was equipped with its standard "tri-cone" roller bit, which measured 4.75 inches in diameter for the All Terrain and 6.00 inches for the RS8/60. The RS8/60 pulled in a 6-inch fluted cone backreamer, and the All Terrain used a 6-inch Rockmaster. Both were pulling in four plastic conduits, each 1.5 inches in diameter. Ground conditions were similar for both, ranging from solid rock and cobble, to caliche and clay.

The numbers in the accompanying table detail the comparison. If you back out the time for making joints on the way out, you'll find that the All Terrain advanced at the rate of 54 feet per hour (fph), vs. the RS8/60's pace of 37 fph. That equates to a rate of 0.90 feet per minute (fpm) for the All Terrain vs. 0.62 fpm for the RS8/60. On the pullback, after the joint-breaking time is backed out, the RS8/60 worked at the rate of 12.8 fpm vs. the All Terrain's 3.75 fpm.

But these numbers need perspective. When drilling, the RS8/60 was cutting a hole 1.25 inches larger than the All Terrain, while on the pullback, using a backreamer the same size as the pilot bore, the RS8/60 was virtually doing no work. The All Terrain, on the other hand, had to grind out 1.25 inches of material on the pullback.

So, maybe the fairest way look at overall performance is to consider the total time each machine needed to complete its job. The All Terrain installed 270 feet of product in 409 minutes, vs. the RS8/60's production of 230 feet in 459 minutes. Thus, the new machine produced 40 feet more in 50 minutes less time. If you factor in the additional 1.5 hours that the RS8/60 needed for set-up and tear-down (see "Comparing Set-Up and Tear-Down"), the net result is that the All Terrain installed 40 feet more product in about 2.5 hours less time than the RS8/60/ Or, approached another way, and we think this is mathematically valid, you can make a ratio to calculate the JT2720 All Terrain's potential production if it worked the same length of time as the RS8/60, 459 minutes. That calculation yields a production figure of 303 feet.

Drilling and Pullback Performance Measurements

RS8/60 JT2720 AT

Bore length (approx.) 230 ft. 270 ft.

Bit type Tri-cone roller Tri-cone roller

Bit size 6.00 in. 4.75 in

Drilling time (total) 6.75 hrs. 5.33 hrs.

Joint make-up time (avg. per pipe) 83 sec. 40 sec.

Backreamer type Fluted cone Rockmaster

Backreamer size 6 in. 6 in.

Pull-back time (total) 54 min. 90 min.

Pull-back rate (avg. per pipe) 45 sec. 160 sec.

Joint breakout time (avg. per pipe) 95 sec. 40 sec.

Pull-back fluid-flow rate 4-5 gpm 7-9 gpm

Pull-back rotation pressure (range) 800-1,000 psi 1,300-1,500 psi. COPYRIGHT 2001 Reed Business Information

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