“Specifically, in the blind-keyway situation, you didn’t really have an option before CNC systems came along,” he said. “We have found that ramping that tool out at a 45° angle, or thereabouts, helps keep that insert intact and clears the chip out of the way.”

Minute Man broaches from duMONT accept keyway inserts, as well as slotting and special inserts, for application on CNC lathes and machining centers. Image courtesy of duMONT.

Turning machine capable of sawing, milling, grinding, gear-cutting, drilling, reaming, boring, threading, facing, chamfering, grooving, knurling, spinning, parting, necking, taper-cutting, and cam- and eccentric-cutting, as well as step- and straight-turning. Comes in a variety of forms, ranging from manual to semiautomatic to fully automatic, with major types being engine lathes, turning and contouring lathes, turret lathes and numerical-control lathes. The engine lathe consists of a headstock and spindle, tailstock, bed, carriage (complete with apron) and cross slides. Features include gear- (speed) and feed-selector levers, toolpost, compound rest, lead screw and reversing lead screw, threading dial and rapid-traverse lever. Special lathe types include through-the-spindle, camshaft and crankshaft, brake drum and rotor, spinning and gun-barrel machines. Toolroom and bench lathes are used for precision work; the former for tool-and-die work and similar tasks, the latter for small workpieces (instruments, watches), normally without a power feed. Models are typically designated according to their “swing,” or the largest-diameter workpiece that can be rotated; bed length, or the distance between centers; and horsepower generated. See turning machine.

Many formations in the U.S. are not well suited to PDC bits. Extremely hard rock and soft formations with hard stringers can often be drilled more economically with roller cone bits than with PDC bits.

Improvements in ROP and bit life allow PDC bits to drill harder formations, previously thought drillable only by rock bits or tungsten carbide insert bits.

Uncoated inserts are acceptable for some applications, such as when broaching aluminum, but Sanieski recommends recoating inserts when cutting materials such as stainless steel and other challenging-to-machine materials.

PDC bits historically have found applications in relatively deep or expensive wells and in soft to medium hard formations. In these wells, the longer bit life, compared with roller cone bits, usually offsets the greater bit cost. ROP ultimately determines the economics of the bit run.

Machine designed specifically to run broaching tools. It is typically designated by operating characteristics (pull, push, rotary, continuous, blind-spline), type of power used (hydraulic, mechanical) and tonnage ratings. Broaching is also performed on arbor presses (manual and powered).

Machining, normally milling, that creates slots, grooves and similar recesses in workpieces, including T-slots and dovetails.

Much of this focus has been on making the diamond layer more abrasion resistant and reducing the stress behind the diamond layer. The bond between diamond layer and tungsten carbide stud is critical for a PDC bit.

The last true revolutionary change in PDC bits occurred in the late 1980s after Amoco Production Co. identified bit whirl, an inefficient mode of drilling. New bit designs and changes in drilling parameters to combat bit whirl have drastically improved bit life and rate of penetration (ROP).

Gardner suggested that maybe a chip was sticking to the end of the insert, causing the insert to pop out. Odekirk thought that scenario would be difficult to verify, but, sure enough, one day he was watching the machine when broaching suddenly stopped. “And there it is; I’m looking at this chip stuck to the end of the insert,” Odekirk said. “Any time you get material welding to your cutting tool, you have a problem. It significantly increases the cutting load.”

Added to titanium-carbide tooling to permit machining of hard metals at high speeds. Also used as a tool coating. See coated tools.

“If you are paying attention and don’t run them too long and start chipping them, you can sharpen them quickly and won’t remove too much material,” he said.

Machining operation in which material is removed from the workpiece by a powered abrasive wheel, stone, belt, paste, sheet, compound, slurry, etc. Takes various forms: surface grinding (creates flat and/or squared surfaces); cylindrical grinding (for external cylindrical and tapered shapes, fillets, undercuts, etc.); centerless grinding; chamfering; thread and form grinding; tool and cutter grinding; offhand grinding; lapping and polishing (grinding with extremely fine grits to create ultrasmooth surfaces); honing; and disc grinding.

For example, Muthig Industries applies broaches from CNC Broach at 550 ipm (13.97 m/min.) when producing blind keyways in parts made of relatively soft cold-rolled steel. (See sidebar below).

Milling cutter held by its shank that cuts on its periphery and, if so configured, on its free end. Takes a variety of shapes (single- and double-end, roughing, ballnose and cup-end) and sizes (stub, medium, long and extra-long). Also comes with differing numbers of flutes.

Advances in metallurgy, hy- draulics, and cutter geometry have not cut the cost of the bits. Rather, they have allowed PDC bits to drill longer or more effectively in a greater number of formations. Another key advantage of these design improvements is the ability of PDC bits to withstand hard formation stringers.

Gardner compares blind-keyway broaching with an indexable-insert tool on a CNC machine to chopping down a tree with an ax. “If you swing the ax really slowly, the ax bounces off of the tree, but if you swing it fast, the ax bites and cuts,” he said.

Nonetheless, Gardner pointed out that even though the operation involves taking a light DOC, it’s essentially a “controlled crash. You’re blasting the tool in there. Broaching is a very shocking operation.”

For shops that resharpen their inserts in-house, duMONT offers an accessory called a sharpening stem. It holds an insert at the correct angle—the angle of the face originally ground into the insert. “You just screw the insert onto the end [of the stem] and buzz it with a grinding wheel,” Sanieski said.

Some of today's PDC bits can drill entire intervals that required two to three PDC bits or five to 10 roller cone bits only a few years ago. The big advantage comes in reducing the number of bit trips and increasing penetration rates, especially for deep wells or those with high rig costs.

The biggest change in the PDC bit industry was identification of bit instability, or bit whirl, by Amoco and the subsequent antiwhirl bit designs. Basically, bit whirl is any deviation of bit rotation from the bit's geometric center.

In addition, Odekirk explained that he examined where the broach was stopping within the cross-hole and determined that a chip breaks out of the hole at 1.9096" (48.5038mm) of the cut length and starts to touch the other side of the hole at 2.1504" (54.6202mm). “So we were stopping about 0.1" past the end of the cutting stroke. I said I’m only going to stop 0.04" past and see if that corrects the issue, because the chips were packing the backside of the hole.”

Even though PDC bits may be considered a specialty tool, their use is still governed in most instances by economics. The decision to run a PDC bit often focuses on cost per foot or total well cost.

When the tool comes out of the hole, the insert shouldn’t touch any metal, Odekirk said, noting the rectangular toolpaths get wider and wider as the broach progresses and makes the keyway deeper and deeper.

The rock strength analysis programs help an operator better determine PDC drillable intervals, make the optimum bit selection, and select appropriate drilling parameters. Such programs have been instrumental in expanding the number of formations drillable by PDC bits.

Resharpening inserts doesn’t suit everyone. Odekirk said Muthig Industries doesn’t resharpen its inserts, which average about 250 keyways per edge, because resharpening changes an insert’s dimensions and makes it nonstandard. “Then you have to either cut, measure and recut to get a good part or retouch the tool off every time you change it,” he added. “I don’t like to live in that world, which is why we also do not sharpen endmill diameters.”

If peculiar wear is found, that information can be used to alter the design of the next bit. Most manufacturers can then redesign and build the new bit and have it on location almost anywhere in the world within a couple of weeks.

Some operators and manufacturers prefer not to take part in such formal agreements because of the speed with which PDC bits undergo improvements. Bits often are left out of many drilling alliance agreements between operators and service companies.

Today's PDC bits drill about 1 1/ 2 times faster than comparable PDC bits in use only 2 years ago. The polycrystalline diamond now used is about twice as abrasion resistant as the diamond used 2 years ago. Many of these types of improvements are considered fine tuning or evolutionary changes in design.

When broaching blind keyways, Ron Odekirk at Muthig Industries emphasized that it’s critical that chips don’t pack together at the end of an indexable-insert tool’s stroke. This essential element was reinforced after the multifaceted parts manufacturer experienced three “pretty significant crashes” when applying indexable-insert broaches from CNC Broach Tool to produce, for an OEM, ¼"-wide × 2"-long (6.35mm × 50.8mm) blind keyways in a family of two different crank adapters made of cold-rolled steel.

Muthig began single-point shaping with CNC Broach indexable-insert broaches after it quoted producing the crank adapters complete in the lathe without manually loading parts into the machine. “We load bar stock into a machine and out comes a finished part that’s ready for packaging and shipping,” Odekirk said, adding that the job involves annually producing 40,000 to 60,000 of each adapter.

Many operators still prefer to choose the bit themselves, usually with assistance from the manufacturer. Manufacturers agree that the most prudent method is to choose a bit based on the interval to be drilled, not on purchase agreements or inventory on hand.

Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.

In general, positive displacement mud motors last longer during drilling. Therefore, bits have to be robust to keep up.

Wheel formed from abrasive material mixed in a suitable matrix. Takes a variety of shapes but falls into two basic categories: one that cuts on its periphery, as in reciprocating grinding, and one that cuts on its side or face, as in tool and cutter grinding.

To achieve the most-effective cutting speed, Gardner suggests holding the broach body in an ER collet with the backstop held directly in a CAT 40 or 50 spindle. He recommends to never hold the shank of the ER collet in a VDI boring bar sleeve to avoid generating taper in the ceiling of the keyway.

PDC bits are less effective in hard, cemented abrasive sandstones, hard dolomites, chert, and granites.

Some companies use cutter force balancing, bit asymmetry, gauge design, bit profile, cutter configuration, and cutter layout to eliminate whirl. Other manufacturers control whirl through engineered cutter placement designed to create a net imbalance force, pushing against the borehole wall, to create a stable rotating condition.

Several service companies and operators use rock strength analysis computer programs to determine the hardness of formations in a well. These computer models use well log analysis techniques and empirical formulas to determine the confined compressive strength of formations to be drilled.

The duMONT sharpening stem holds an insert securely in place as the cutting edge of the insert is resharpened at its original angle. Image courtesy of duMONT.

The typical product life is about 2 years, and the number of variants of a particular design are increasing rapidly.

“Speed is your friend” when broaching, Gardner added, but many users are afraid of hurting their CNC machines when applying the tools. Depending on the workpiece material, “I have to constantly remind them that they’re only taking a 0.001" depth of cut,” he said. “It’s just a very light shave. There is virtually no force involved. You could push that through with your hand.”

Odekirk said he learned about the benefits of CNC Broach Tool’s broaches online and, after watching a demonstration video, determined “if they can do it, we can do it; we just need to get a broach in here and figure it out.”

Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.

The U.S., by contrast, has many areas in which rig day rates are relatively low, especially onshore. That makes the economics of running PDC bits less favorable.

General Electric introduced PDC in 1973. Bits with PDC cutters became commercially available the following year.

Being able to broach a blind keyway while keeping the part on the same CNC machine tool used to perform the other machining operations provides a significant improvement in setup, reliability and accuracy, compared to moving the part to a dedicated broaching machine.

With those corrective measures in place, Odekirk said Muthig Industries continues to apply the broaches from CNC Broach Tools to produce crank adapters and has not experienced any crashes or other issues. “We are definitely familiar and comfortable with the technology and the manufacturer.”

PDC bits usually have applications when long on-bottom times are important, oil-based muds are used, or water-based muds are used in nonhydrating formations. PDC bits also are advantageous for high rotational speed drilling, such as with a turbine or mud motor, or for drilling deviated hole sections.

Measure of the relative efficiency with which a cutting fluid or lubricant reduces friction between surfaces.

Image

Hughes Christensen(27064 bytes) predicts diamond bits will account for almost 25% of world footage drilled by 1997. About 10 years ago, PDC bits had only 10% of the market.

When blind-keyway broaching, CNC Broach Tool recommends creating a relief area in the part to push chips into and prevent chip packing. The types include cross-hole (top), groove (middle) and notch (bottom).  Images courtesy of CNC Broach Tool.

Improvements in PDC bit stability, hydraulics, and cutter design have contributed to increased footage per bit in recent years. Roller cone bits also have shown improvement in performance.

Designing and building a new bit has become very fast, mainly because of advances in CAD/CAM and engineering practices. PDC bits have become a specialty tool, not a commodity that can be bought in large number in advance of need.

They also can be used in low strength, poorly compacted, nonabrasive, shallow sediments, precipitates, and evaporites -- for example, salts, anhydrites, marls, and chalk -- and in moderately strong, somewhat abrasive and ductile formations such as silty claystone, siliceous shales, porous carbonates, and anhydrites.

The technology to minimize downhole vibrations has yielded longer bit life, faster penetration rates, and reduced drilling costs.

Odekirk said the crashes, the first of which happened a day or two after production began, didn’t damage the main spindle on the company’s Doosan 2600SY lathe, but they did permanently damage three tool bodies when the insert popped out. After each "full, hard crash," the machine was out of alignment, which required half a day to correct, he added.

That’s according to Kevin Sanieski, CNC tooling system lead for The duMONT Co. LLC, Greenfield, Mass. One effective method is to use broaches that accept inserts, and the toolmaker offers those in its Minute Man line for application on CNC lathes and machining centers.

Using a shaper primarily to produce flat surfaces in horizontal, vertical or angular planes. It can also include the machining of curved surfaces, helixes, serrations and special work involving odd and irregular shapes. Often used for prototype or short-run manufacturing to eliminate the need for expensive special tooling or processes.

Some of General Electric's original PDC patents expired during the past few years, opening the market to many small PDC manufacturers.

Flexible-sided device that secures a tool or workpiece. Similar in function to a chuck, but can accommodate only a narrow size range. Typically provides greater gripping force and precision than a chuck. See chuck.

BP ran a 171/ 2-in. Hycalog PDC bit on the BA-X14 well in Colombia's Cusiana field, where offset well BA-X11 on the same drilling pad required two PDC bits, one from Hycalog and one from another manufacturer, for the same interval

These bits, most of which use PDC cutters, generally drill the more critical, expensive wells around the world. Diamond bits account for almost one third of the world bit market, and sales exceed $200 million/year, the U.S. Department of Energy reports.

Sanieski added that the broaching system is not only suitable for generating keyways but also splines, squares, hexes and other internal and external features. “Anything you can think of, we can match a profile.”

“We want to have enough relief space so you’re not pounding chips in there,” Gardner said. “That’s the ultimate goal for blind-keyway broaching.”

Operation in which a cutter progressively enlarges a slot or hole or shapes a workpiece exterior. Low teeth start the cut, intermediate teeth remove the majority of the material and high teeth finish the task. Broaching can be a one-step operation, as opposed to milling and slotting, which require repeated passes. Typically, however, broaching also involves multiple passes.

Advances in polycrystalline diamond compact (PDC) bits have sharply increased penetration rates(31588 bytes) in oil and gas wells.

PDC cutters consist of a layer of bonded diamond particles backed up by a thicker layer of tungsten carbide.

Larger hole sizes are generally thought uneconomic for PDC bits because large holes are typically shallow and easily drilled by roller cone bits. The high cost to manufacture such large PDC bits usually is not justified. One operator in South America, however, used recently 26-in. PDC bits with success.

Exeter received proprietary rights to the bit, and Hughes Christensen developed a new bit it could manufacture for costs similar to that of old style bits.

Tapered tool, with a series of teeth of increasing length, that is pushed or pulled into a workpiece, successively removing small amounts of metal to enlarge a hole, slot or other opening to final size.

Fluid that reduces temperature buildup at the tool/workpiece interface during machining. Normally takes the form of a liquid such as soluble or chemical mixtures (semisynthetic, synthetic) but can be pressurized air or other gas. Because of water’s ability to absorb great quantities of heat, it is widely used as a coolant and vehicle for various cutting compounds, with the water-to-compound ratio varying with the machining task. See cutting fluid; semisynthetic cutting fluid; soluble-oil cutting fluid; synthetic cutting fluid.

Diamond is 10 times harder than steel and twice as hard as tungsten carbide. Diamond also is the most wear resistant material known. It has a wear resistance about 10 times that of tungsten carbide. Diamond, however, is brittle and susceptible to impact damage.

There is no single solution to hydraulics problems at the bit. Each company has a slightly different technical perspective. The goal is to clean the bit effectively but not to erode it with mud flow through nozzles.

Some new synthetic muds, based on mineral oils or glycerin, and friction-reducing additives for water base muds have helped improve PDC bit penetration rates compared with that in typical water based muds.

The insert was relatively fresh, with its coating still intact, so Odekirk said he examined the coolant line. Coolant was flowing through an ER32 collet, but spraying along the length of the tool without a clearly defined coolant jet directed at the chip. The company changed the coolant line so the flow was directed at the tool/workpiece interface and not just spraying everywhere. “Before, it was like cutting underwater,” he said.

Bit whirl can be caused by cutter/ rock interaction forces and things such as formation characteristics and undesirable bottom hole assembly motions. Conventional PDC bit technology provides little resistance to whirl and may reinforce whirl once it starts.

Image

Cutters are no longer limited to a 13-mm round shape. They come in various sizes (8 mm to 19 mm) and shapes. A few companies have had success with dome shaped cutters.

What's more, design improvements have allowed PDC bits to drill harder formations and soft formations with hard stringers, previously thought to be drillable only by roller cone bits.

Inserts from CNC Broach, which come coated with TiN, can also be resharpened, sometimes up to nine times, and most of its customers do not recoat them after resharpening, Gardner said. “I feel the coating helps get maybe two extra keyways per cutting edge, but with our product you’re already getting 100 to 200 keyways per cutting edge.”

The company states that it designed the insert to pop out of the tool pocket to protect the machine spindle if there is not enough relief space. “Don’t get mad and blame the tool,” Gardner stated. “This is a clue that you do not have enough relief space or the chips are not evacuating the relief space and you are pounding into them.”

Much of the knowledge on how to run PDC bits properly flowed from Shell International Petroleum Co. Ltd.'s research on torque and vibration problems, Amoco's antiwhirl developments, and work by other major oil companies and service companies.

Furthermore, operators in the U.S. still drill many shallow wells. So the ability to reduce the number of trips or trip time is not as significant as in deeper wells.

Some operators and manufacturers work together informally, usually to improve bit design by adding specific features to suit a given formation.

CNC Broach’s tools have setscrews on the side, but the carbide inserts are open face, Gardner explained, and the design of the insert directs the cutting force down into the tool centerline and seats the insert down and back in the tool body’s pocket. This design protects the machine if the insert, which has two cutting edges, experiences a lot of pushback or chips buildup in the relief area, he said.

Each manufacturer has a slightly different design concept, and no one design seems to stop or prevent whirl in all situations.

Image

Recent advances in metallurgy have allowed use of various PDC cutter geometries. These cutters are less susceptible to breakage and can withstand stress better.

PDC bits generally work better in oil based muds than in water based muds. Oil-based muds, however, are not viable options in many areas because of environmental regulations and the high cost of disposal or treatment. As a result, many operators may use water based muds.

Space provided behind the cutting edges to prevent rubbing. Sometimes called primary relief. Secondary relief provides additional space behind primary relief. Relief on end teeth is axial relief; relief on side teeth is peripheral relief.

At about $10,000-150,000 apiece, PDC bits generally cost five to 15 times more than roller cone bits. But a PDC bit run in the proper application can substantially lower total drilling costs despite the higher initial expense.

As PDC bit use has become more widespread, directional drillers and drilling engineers have become more familiar with the proper operational parameters to run a PDC bit successfully in a given formation. Those parameters include weight on bit, mud pressure, flow rate, and rotational speed.

While the vast majority of indexable inserts are disposed of or recycled once they are worn, Sanieski said duMONT’s broaching inserts, which contain 13 percent cobalt and are heat-treated to a hardness greater than 68 HRC, can be resharpened up to five times, depending on insert condition and, therefore, how much material must be ground off.

CNC Broach Tool offers indexable-insert tools for broaching blind keyways. The tools have setscrews on the side, but the inserts are open face. Image courtesy of CNC Broach Tool.

When broaching on a lathe, the workpiece is positioned horizontally and gravity causes chips to fall down and away. Not so when broaching on a mill. With a mill, Gardner recommends creating a cross-hole, groove or notch relief in the part—an open area to push the chips into.  The relief area needs to be large enough that coolant doesn’t simply flush and pack the chips into it, however. If the relief area is not large enough, the tool will pound into those packaged chips and potentially cause a crash, he said, adding that coolant flushes the chips right through a cross-hole and avoids that.

The duMONT Minute Man tooling system allows users to broach through and blind keyways, keyways in a tapered bore and shaped or splined holes. Image courtesy of duMONT.

Whichever approach is most economical, Gardner emphasized the need to make a mental leap when it comes to broaching on CNC lathes and mills. “People have this whole backwards notion about broaching on a CNC machine,” he said. “They just can’t visualize a different way of doing it, so they have a resistance to doing it on their lathe or mill.”

PDC bits are most effective in very weak, poorly consolidated, brittle, hydratable sediments -- sands and silts, for example.

PDC bit design improvements are driven by research, good engineering practices (finite element analysis, accurate analysis of dull bit grading, rock strength analysis, and the like), and fierce competition from other PDC bit manufacturers and the rock bit industry.

Historically, two factors have been mainly responsible for limiting the operating range and economics of running PDC bits: shortened life because of cutter fracture and slower ROP because of inadequate cutter cleaning.

One of the biggest limitations on high penetration rates is the need to avoid overheating the PDC. The PDC wafer and tungsten carbide base have different coefficients of thermal expansion, which can lead to cracking at high temperatures.

Enlarging a hole that already has been drilled or cored. Generally, it is an operation of truing the previously drilled hole with a single-point, lathe-type tool. Boring is essentially internal turning, in that usually a single-point cutting tool forms the internal shape. Some tools are available with two cutting edges to balance cutting forces.

John Gardner, owner of CNC Broach Tool LLC, Marina Del Rey, Calif., agreed that users can ramp, or taper, an indexable-insert broach out of a blind keyway when broaching it, but maintains that the programming required to do so is difficult to perform. In addition, the design of the broaching tool CNC Broach Tool offers isn’t well-suited for ramping out of the cut.

CNC machine tool capable of drilling, reaming, tapping, milling and boring. Normally comes with an automatic toolchanger. See automatic toolchanger.

A chip became welded to an insert during blind-keyway broaching at Muthig Industries. ​Image courtesy of Muthig Industries.

The company did and produced five samples of each part, which the customer approved, without any issues, according to Odekirk. To break the chips and prevent them from packing at the end of the blind keyway, Muthig machines a cross-hole relief in each part, which is more suitable for this particular family of parts because adding a groove or notch relief would create a thinner wall that could reduce part strength.

Ron Odekirk, production manager for Muthig Industries Inc., Fond du Lac, Wis., a parts manufacturer that applies tools from CNC Broach to broach blind keyways, described the toolpath as rectangular, and said the tool is fully withdrawn from the workpiece when it retracts from the hole after each cut.

Runs endmills and arbor-mounted milling cutters. Features include a head with a spindle that drives the cutters; a column, knee and table that provide motion in the three Cartesian axes; and a base that supports the components and houses the cutting-fluid pump and reservoir. The work is mounted on the table and fed into the rotating cutter or endmill to accomplish the milling steps; vertical milling machines also feed endmills into the work by means of a spindle-mounted quill. Models range from small manual machines to big bed-type and duplex mills. All take one of three basic forms: vertical, horizontal or convertible horizontal/vertical. Vertical machines may be knee-type (the table is mounted on a knee that can be elevated) or bed-type (the table is securely supported and only moves horizontally). In general, horizontal machines are bigger and more powerful, while vertical machines are lighter but more versatile and easier to set up and operate.

“You can basically run them in any lathe or milling machine,” Sanieski said. “Obviously, the bigger and more rigid the machine, the better the tools will operate.”

The OEM, which had been producing the adapters in-house, turned the parts in a lathe and then moved them to a vertical machining center for broaching, he noted.

The challenge when applying this type of tool is that if a user cuts a blind keyway, simply retracts the tool from the cut and then continues to broach, the chips continue to build up at the bottom of the keyway and the insert inevitably becomes damaged, Sanieski explained. Therefore, the company provides a CNC program with its keyway broaching system that promotes continuous tool movement and cutting while eliminating the need to manually clear chips.

Machining operation in which metal or other material is removed by applying power to a rotating cutter. In vertical milling, the cutting tool is mounted vertically on the spindle. In horizontal milling, the cutting tool is mounted horizontally, either directly on the spindle or on an arbor. Horizontal milling is further broken down into conventional milling, where the cutter rotates opposite the direction of feed, or “up” into the workpiece; and climb milling, where the cutter rotates in the direction of feed, or “down” into the workpiece. Milling operations include plane or surface milling, endmilling, facemilling, angle milling, form milling and profiling.

About 75% of the PDC bit market lies outside the U.S., say Diamond Products International Inc. and Security DBS. Many non-U.S. areas have relatively soft formations or are expensive to drill because of high rig day rates, remote or offshore locations, or deep wells. Those factors present favorable economics for PDC bit use.

Engagement of a tool’s cutting edge with a workpiece generates a cutting force. Such a cutting force combines tangential, feed and radial forces, which can be measured by a dynamometer. Of the three cutting force components, tangential force is the greatest. Tangential force generates torque and accounts for more than 95 percent of the machining power. See dynamometer.

Commercial practical limits for PDC bit sizes have been 31/ 2-in. and 171/ 2-in. diameters. These limits are due mainly to economics, not technology.

Round cutters with a buttress or beveled edge have significantly improved PDC bit performance in several areas. These cutters have worked well in applications in which cutting elements are subjected to high impact loads, such as in hard formations, dynamically unstable drilling, or highly interbedded formations.

2-D or 3-D path generated by program code or a CAM system and followed by tool when machining a part.

For example, Enron Oil & Gas Co. and Diamond Products International have such an agreement in which Enron helped design a new PDC bit for an area in the Gulf of Mexico where PDC bits have been used successfully for years. Although previous PDC bits worked well in the area, changes in hydraulics design, cutter layout, and blade spiraling increased penetration rates 20-30%.

Odekirk added that Muthig also increased coolant concentration to enhance its lubricity and antiweld characteristics.

This diamond/tungsten carbide interface can be made successfully with various geometrical shapes, instead of conventional flat surfaces, to reduce stress on the diamond face during drilling. As these premium cutters wear, there is more diamond remaining on the stud to continue cutting. This nonplanar geometry has significantly lengthened cutter life downhole.

For example, BP Exploration Co. (Colombia) Ltd. used only one newly designed PDC bit in place of two other PDC bits to drill an interval in a well in Colombia. It saved $419,000 because of the faster ROP and one less bit trip.

Although most PDC still comes from General Electric and De Beers, several smaller companies have begun making high quality diamond wafers. This increased competition has not reduced cutter cost, mainly because PDC manufacturing is an expensive, capital intensive process.

Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).

Bit whirl patterns can cause the PDC cutters diamond table to chip or spall, accelerating wear and decreasing bit life.

As PDC bit design improves, the bits tend to drill longer intervals, and many can be used in several wells. In such cases, footage drilled per bit is more important than the number of bits used.

The dimensions (in inches) for when a chip breaks out of a cross-hole and when it starts to touch the other side of the hole, along with a selection of chips produced when broaching blind keyways. Image courtesy of Muthig Industries.

Furthermore, the cost of tungsten carbide, used in the stud that holds the diamond, has increased during the past few years.

During whirl, the instantaneous center of rotation of the bit changes, instead of staying in line with the borehole center. Cutters can move laterally and even backwards relative to the local rock surface.

Another relatively recent advance is the use of polished diamond cutters. The polished PDC surface has a significantly lower coefficient of friction, preventing cuttings from building up on the cutter surface.

The new bit drilled 1,338 ft in 145.8 rotating hr for an average ROP of 9.2 ft/hr. The two bits run in the offset well drilled a total 1,017 ft at an average ROP of 6.3 ft/hr.

Bit performance economics are measured in terms of cost per foot drilled. This involves factors such as bit cost, footage drilled, time spent drilling, trip time, and daily rig costs.

Improvements in computer aided design and computer aided manufacturing (CAD/CAM), along with improvements in dull bit grading, allowed optimization of bit design for specific applications.

In one case, Exeter Drilling Corp. and Hughes Christensen formed an alliance to design a PDC bit that would drill wells in the Denver-Julesberg basin of the Rocky Mountain region fast but with reduced pump pressure. They codeveloped a 77/ 8-in. multiport PDC bit that drilled more than 75,000 ft without repair, averaging 103.2 ft/hr.

Cone-shaped pins that support a workpiece by one or two ends during machining. The centers fit into holes drilled in the workpiece ends. Centers that turn with the workpiece are called “live” centers; those that do not are called “dead” centers.

If the price premium for a PDC bit is less than the value of the saved drilling and tripping time, the PDC bit will be the most economic choice.

Essentially a cantilever beam that holds one or more cutting tools in position during a boring operation. Can be held stationary and moved axially while the workpiece revolves around it, or revolved and moved axially while the workpiece is held stationary, or a combination of these actions. Installed on milling, drilling and boring machines, as well as lathes and machining centers.

To try and prevent further crashes, Odekirk consulted with CNC Broach Tool’s John Gardner, who recommended a larger cross-hole for the relief, but the customer didn’t want any revisions to the part design. “They said, ‘We’ll manufacture them ourselves if you guys can’t figure it out,’” Odekirk said. “We said, ‘We’ll figure it out, no problem whatsoever.’”

Sources such as service companies, operators, vendors, and investment bankers use various methods to gauge the success and growth of PDC bits in the drilling industry. Some market analyses include the number of bits sold or purchased, footage drilled per bit, or bit revenue.

That mentality can quickly change, however, after a shop outsources, say, a couple hundred parts that need blind keyways to be EDMed at $25 a part and receives the parts with incorrect keyways 2 or 3 weeks later. “If you can blind-keyway broach in your own house, you’re saving money, time and the chance that somebody won’t scrap your parts,” Gardner said. “How do you beat that?”

The use of dual powerhead motors, basically two positive displacement mud motors in tandem, has helped stabilize downhole torque. Other improvements in bottom hole assembly components have helped minimize torque and whirl problems.

Main body of a tool; the portion of a drill or similar end-held tool that fits into a collet, chuck or similar mounting device.

Economic success of the first PDC bits stemmed from high operating costs for the rig and use in very select geological intervals. In the early 1980s, PDC bits underwent true engineering to suit specific field applications.

The bottom hole pattern (left) of a whirling PDC bit has an irregular pattern, whereas the bottom hole pattern (right) of an antiwhirl PDC bit shows smooth drilling.

Alan holds a bachelor’s degree in journalism from Southern Illinois University Carbondale. Including his 20 years at CTE, Alan has more than 30 years of trade journalism experience.

Operators and bit manufacturers have developed many ways to prevent bit whirl and overcome or minimize it when it shows up.

Cost of the bit may be only about 2-3% of total well cost, yet the bit can affect up to three-fourths of the total cost.

Hughes Christensen has formed many successful alliances with operators. Many of such alliances focus on a technical objective.

Distance between the bottom of the cut and the uncut surface of the workpiece, measured in a direction at right angles to the machined surface of the workpiece.

Hardness is a measure of the resistance of a material to surface indentation or abrasion. There is no absolute scale for hardness. In order to express hardness quantitatively, each type of test has its own scale, which defines hardness. Indentation hardness obtained through static methods is measured by Brinell, Rockwell, Vickers and Knoop tests. Hardness without indentation is measured by a dynamic method, known as the Scleroscope test.

Value that refers to how far the workpiece or cutter advances linearly in 1 minute, defined as: ipm = ipt 5 number of effective teeth 5 rpm. Also known as the table feed or machine feed.