Greenstone and sedimentary formations like mudstone and conglomerate, while variable, are typically low in Moh’s hardness. Moving into the actual ore zone, the formation consists of various types of rock such as feldspar, muscovite schist, and fragmental biotite, introducing abrasiveness related to the rock’s quartz content.

The challenge in softer abrasive formations is to pick a diamond drilling bit tough enough to get good life without sacrificing penetration rate.

Adding in the drive for productivity creates an additional challenge. The driller cannot simply pick the toughest bit available; life needs to be increased while still maximizing penetration rate or tripping out rods to change bits impacts overall productivity.

Using patented technology, the new Longyear Bits have diamonds that are chemically bonded to the matrix creating a more versatile, faster penetrating, and a longer-lived bit. All drillers from the newly promoted to the seasoned veteran find the color-coded Longyear Diamond Bits considerably more effective in obtaining higher productivity. For each hardness rating on Mohs hardness scale, Boart Longyear has created a recommended color. The complete line of Longyear Diamond Bits includes a Red, Orange, Yellow, Green, Blue, and Purple Bit.

Originally, Alpha series 08 and 09 were chosen in Stage3 to get a good combination of life and penetration rate. These bits, while achieving acceptable penetration rates, fell significantly short on life at 43m, the average over three months. In looking at the Longyear Bit series cross reference chart, Alpha series 08 and 09 would be replaced by the Longyear Green bit. Given the low hardness of the formation, the Longyear Blue bit was also selected to determine the best solution. In stark contrast, to the Alpha series bits, the penetration rate and bit life both increased. Using a combination of the Longyear Blue and Green bits, driller’s averaged 109 meters per bit and increased penetration rate. When drilling softer formations at site, the drillers used the Blue bit and found this bit to be incomparable when looking at the production rates and bit life. The two formulas combined yielded a 60% improvement in life and an 8% increase in productivity.

Boart Longyear Canada East Coring Supervisor, Jeremy Dykstra said, “In the beginning, we struggled to meet our production targets due to slower penetration rates and poor bit life. Once we started to trial the new Longyear Diamond Bits, the performance improvement was noticed immediately with all crews at site. Smoother cutting of the formations and longer bit life helped push us towards the successful and safe production shifts we aimed to have both for our client and our business.”

Established in 1890, Boart Longyear is the world’s leading provider of drilling services, drilling equipment and performance tooling for mining and drilling companies.

The Global Drilling Services division operates for a diverse mining customer base spanning a wide range of commodities, including copper, gold, nickel, zinc, uranium, and other metals and minerals. The Global Products division designs, manufactures and sells drilling equipment, performance tooling, down-hole instrumentation and parts and services.

Ready to take the Longyear Bit challenge? Contact your Boart Longyear representative today to order trial bits and download this blank bit log sheet to keep track of bit performance so you can compare the productivity and speed of both your current diamond bits and Longyear Bits.

The Drilling Services Surface Coring drill crew used the powerful LF350e along with the new, patented XQ wireline coring rods featuring W-Wall, and the new Longyear diamond bits to successfully directionally drill at an angle of 65 degrees to the client’s required depth – which was almost 10,500 feet (3200 meters). An impressive feat in and of itself, the project had measurable productivity gains and proved the newest Boart Longyear rigs and tooling make a real difference in the field. 

With innovative features of the drill rig, combined with the deepest rated coring rods in the market and the fastest, smoothest cutting bits, the project’s success was also attributed to the talent, experience, and technical expertise of the crew.

Boart Longyear has combined proven technology from its most popular surface coring drill rigs to create the powerful LF350e.The forward tilting head design simplifies the rod handling process and reduces the need for operator intervention and maintenance. The rod breaking clamp is a hydraulic breaking device which means no wrench under power. The foot clamp rotates to break rod joints located between the foot clamp and rod breaking clamp. The rig also features a heated and air conditioned drillers cab to protect the operator from the elements and overhead hazards. Utilizing CAN bus communication and PLC programming, all LF350e functions are controlled electronically. The “e” in LF350e refers to the fully electronic control system. The rig is designed ergonomically to lessen fatigue and stress to the driller and helper. The LF350e has adjustable wireline speed to be able to set to lower the over shot and then pull the tube, which allows a hands-off safer approach. This is just one-way ergonomic design plays a part in reducing fatigue with this drill rig. The beauty of Boart Longyear’s business model of both contract drilling services and a drilling products business is access to immediate, direct, unfiltered feedback from drillers in the field. Drill rigs built for drillers.

A unique combination of -20 degree self-locking reverse flank angle on the threads and symmetrical load distribution when combined with W-Wall double-annealed mid-body, make XQ wireline coring rods some of the deepest rated coring rods in the market. XQ has an increased negative flank angle from of -20 degrees compared to -10 degrees in RQ rods. The increased negative flank angle combined with the double-start threads, nearly eliminate box bulging and provides greater strength in high torque applications.

Patented XQ joints have opposite double-start threads that are self-aligning so mating engages smoothly. This provides a balanced load response and double the contact area, which means half the contact pressure. This symmetrical load distribution increases load capacity significantly for stronger rods with deeper capacity. The lighter drill string increased drill rig depth capacity and reduced fatigue in driller's when manually tripping. The enlarged inner diameter also significantly reduced inner tube tripping time for improved productivity.

The new NXQ and HXQ W-Wall coring rods feature patent-pending, double-upset tubing, with the same overall weight reduction and faster wireline tripping speed as V-Wall. However, the standard wall thickness in the middle of XQ rod eliminates premature mid-body wear and resists bending, performing like straight wall tubing.

As all Boart Longyear coring rod, XQ W-Wall tubing is cold-drawn from high quality, North American alloy steel, uniquely processed to Boart Longyear specifications.

Boart Longyear has successfully created a chemical bond between diamond and matrix, which is stronger than the diamond itself. The increased diamond projection and improved face flushing create a bit with more versatility, higher penetration rates, and longer life. The Longyear Bits are similar to large diamond bits, but with the easy, smooth drilling characteristics drillers prefer. This means increased productivity throughout the entire operation, and ultimately more core.

To support higher penetration rates, the new Longyear formulas are combined with a new, more open, express geometry. Tapered intermediate waterways improve flushing and prevent accumulation of debris. Designed for fast cutting in competent ground, the new express geometry is available in our 16mm crown heights to maintain bit life at higher cutting speeds.

The unique Razorcut protrusions on the face of the bit contain diamonds that enable the bit to begin cutting right out of the box – even in the softest ground. The arrangement of these protrusions also improves the tracking and balance in the hole when drilling begins.

When the right drill bit is in the right ground operated under the right conditions, more core ends up in the box at the end of a shift. There isn’t a perfect drill bit matrix or geometry that cuts every ground as quickly as possible. A Longyear bit may cut 17 inches per minute in Arizona, but cut just three inches per minute in Ontario.

Although diamond drill bit selection is often an afterthought, it’s just as important as drillers deciding how much water/mud to run or how fast to spin rods.

There are many factors to consider when selecting a drill bit, including the main objective of a project. As mentioned, the overarching objective is always more core in the box, but there are additional elements that need to be considered. For example, a rod trip takes significantly less time at 400 feet than a rod trip at 4,000 feet. While bit life is important, it’s less crucial at the top of a hole because that usually means sacrificing penetration rates.

In Australia, a site used two different bits at different depths. A Longyear Red Express bit was used to cut 60 centimeters per meter with a life of only 120 meters at the top of the hole. Once that bit was done they switched to a Longyear Yellow Stage 3, because rod tripping took too long. With this bit they only cut at 35 centimeters per minute but achieved a life of 300 meters per bit. Using a singular Longyear bit, this site put 6% more core in the box than they did with a competitor’s bit. However, using these two Longyear bits in tandem, they saw a 23% increase of core in the box over the competitor’s product. Sometimes, it’s more beneficial to cut faster even if it means tripping more.

Once a driller decides whether the objective is cutting faster or tripping less often, next it’s important to establish how hard the ground is to cut. Contrary to popular belief, the ground drillers cut is (probably) not the hardest ground on earth. This is where the Mohs scale comes into play. The Mohs scale is an exponential scale from 1 to 10 to quantify mineral hardness. Minerals with a higher Mohs hardness will scratch anything with a lower Mohs hardness. For example, a mineral classified as a four will scratch a three but not a five.

All the bits offered on the market today are targeting a specific range of the Mohs scale for the best performance. To determine the Mohs hardness of the rock to be drilled, a Mohs hardness scratch test kit is needed. This kit is a series of picks made of different materials that, when used properly, can determine the Mohs hardness plus or minus 0.5.

The Boart Longyear scratch test kit has four scratchers with eight replaceable tips and a sharpening stone. If the numbered tip scratches the rock, the rock is softer than the number on the tip. If a seven scratches and a six doesn’t, you know you’re in 6.5 rock. You would then select the bit created for that rock.

Once ground hardness is identified, Boart Longyear offers a Longyear Diamond Bits Hardness Rating & Comparison Chart to find a recommended bit for that ground. For example, Purple is meant for 1 - 4.5 rock, up to Red which is best for 7.5 – 9. Purple covers such a large range numerically because the Mohs scale is exponential (1 and 4.5 on the Mohs scale are closer together on “true” hardness than 7.5 and 9).

In the cross reference above, bit range overlaps, and the bars representing each drill bit are quite long. This is where the objectives of the site come into play. For example, if you are in a 6.5 rock, select a Green Bit or a Yellow Bit. Which one should you try first? It depends. If the site is cutting a lot of short holes and bit life isn’t a big concern, you would likely have the best luck with Yellow – it would penetrate faster than Green, but not have as long of life in 6.5 rock. On the flip side, if bit life is a concern because you’re drilling deep holes, you may prefer Green.

Another thing to consider for bit selection is geometry. While the Green bit is, in general, tougher than the Yellow, a Green bit with more open area and a Yellow with less open area will exhibit very similar cutting characteristics.

The geometries offered by Boart Longyear are all designed to cut a little differently. Within each color bar, the Express has the ability to cut harder rock than the Stage and the Stage will cut harder rock than the Tapered Waterway. This is a result of what is called, “open area”.

Open area is determined by finding the surface area of a disc with the same outside diameter and inside diameter as the drill bit, and subtracting the surface area of the drill bit with all the waterways cut in. What’s left is the area of the waterways, flutes, and rounds, and the percentage of this number compared to the area of the total disc is the open area. Express has an open area of 30%, Tapered Waterway has an open area of 25% and Stage has an open area of 20%.

Standard Waterways

• Most common waterway style
• Longest life based on lowest open area 15%

Tapered Waterways

• Pushes cuttings to the OD and reduces pressure across bit face
• Open area 25%
• Preferred

Express Waterways

• Faster penetration and/or lower weight
• Open area 30%
• Free-cutting formulas

Stage/GT

• Wide waterways, more versatile
• Better flushing and penetration than standard waterways
• Open area 20% for Stage

Deep ID Waterways

• Recommended for lost circulation applications; prevents the lifter case pulling into the bit and shutting off water
• Can be used instead of face discharge in triple-tube and piloted core lifter case
• Face Discharge preferred for core recovery. Open area based on waterway

Face Discharge Waterways

• Reduces water pressure on the core and redirects fluid to the face of the bit (reduces washing core material), aiding in core recovery
• Required for piloted core lifter cases
• Open area based on waterway

If cutting at the top range of these bars, more open area will be needed, and the Express, for the middle and bottom ranges, will use Tapered Waterway or Stage, respectively.

The Longyear Yellow and the Longyear Green bits overlap substantially in the cross reference. This shows either the Longyear Yellow or the Longyear Green can cut Mohs 7 rock. To cut this Mohs 7 quickly, a Yellow Tapered Waterway bit will be needed. To cut it more slowly and optimize bit life, a Green Stage bit should be used. A Green Express, a Green Tapered Waterway and a Yellow Stage would land somewhere in-between.

Once a bit has been selected for the rock type, crown height, and geometry, the last step is to collect data and test the chosen bit’s performance.

Once the ideal bit has been identified – it needs to be tested, and the only way to make an informed decision during testing is to collect data.

Here are three mandatory data points to collect:

• Penetration rate on every run
• Mohs hardness every run
• Bit life of every bit

Once the data has been collected, this information can be used to either validate the choice initially made or adapt based on unaccounted circumstances. For example, if the Green Stage bit was selected but the penetration rate wasn’t as high as expected, then the Green Express and the Yellow Stage would be good bits to try next. The Yellow Stage may not provide the desired life, but the Green Express may be a perfect in-between. All this shows in the data and at the end of the day more core ends up in the box.

With a combination of knowledge, the right tools, and good planning, every shift can be optimized, and subsequently, put as much core in the box as possible.

Learn more about bit optimization and the productivity results from the field - New Longyear Bits Put 23% More Core in the Box

Ready to start testing? Contact your local Boart Longyear representative or visit My Drill Store.

Chris Lambert has a bachelor’s degree in mechanical engineering and has been with Boart Longyear since 2008. He has been the company’s global product manager for coring tools, including rods, in-hole tools and diamond bits, since 2012. Prior to that, he was the engineering manager for diamond products. His 20-year engineering and product development career has included materials, hydraulics, pumps and diesel engines.

Our new host, Jon Peterson (Geo Jon for fun), works for the Products division as a Customer Service Representative. Jon graduated from the University of Utah in 2015 with his Bachelors of Science in Geology. He’s worked for Boart Longyear for the last two and a half years and interned as a geologist with an exploration company for about six months prior to coming to work for Boart Longyear. Jon has been married for a year and a half and in his free time enjoys trail running, hiking, working on his yard, spending time with family, and playing with his black lab Dexter. 

Learn more about the Longyear bits.

We would love to hear your questions and comments below. Thanks for listening and if you liked this episode, share it on LinkedIn, Facebook, or Twitter. 

Rotational speed has a direct influence on the penetration rate of bits. If the speed is doubled for a given depth of a cut, the penetration rate also doubles. For this reason, rotational speed is typically set at a fixed value based on the size of the tools being used. If the rig has sufficient torque, the speed can be increased to get higher penetration rates. Conversely, if the head stalls under normal operation, then the speed should be reduced to produce more torque and maintain steady rotation. The exception to this rule is drilling in extremely broken and hard ground. Broken ground is free to move so instead of cutting, the rock is removed by a grinding action. Under these conditions (three body wear), diamond bit wear is extremely rapid and rotational speed should be cut to half RPM and weight on bit sufficient to reach 1 to 2 ipm (3 to 5 cpm).

If the head stalls under normal operation, reduce the speed to produce more torque and
maintain steady rotation.

In broken ground, cut RPM in half and apply sufficient weight on bit to reach 1 to 2 ipm 
(3 to 5cpm).

Weight on bit (WOB) is the main method of controlling bit life and penetration rate. If very high bit loads are required to cut the rock, select a higher series bit to prevent increased hole deviation, excessive core barrel, and rod wear, and even down-hole failures. Increasing the bit series normally results in lower bit weights required for the same penetration rates. If weight on bit is too low, both the penetration rate and torque drops, resulting in low life and productivity. This condition is referred to as polishing and describes the phenomenon of diamonds wearing faster than the matrix until the face is flat, leaving no diamonds protruding from the face. Polishing is caused by the friction and heat accumulating in the diamond as it rubs rather than cutting the rock. If weight on bit is too high, characterized by very little or no increase in penetration rate for additional weight, the result is constant sharpening and rapid wear.

WOB is too low if the bit polishes and torque drops. Results in low life and penetration rate.

WOB is too high if added weight does not increase penetration rate. Results in constant sharpening and rapid wear.

Sharpening of the bit results from burying the diamond in the formation and creating contact between the matrix and formation. The friction on the matrix removes it and exposes new diamonds. Sharpening is beneficial when bit penetration has dropped due to wear on the diamonds but if left in a sharpening mode the bit is consumed very rapidly. As rods are added, force to maintain constant weight on bit will change, so weight on bit must be monitored to ensure consistent bit performance at all depths. The weight of the rods and the down force developed by the hydraulic cylinders provide the force exerted on the diamond bit. Unfortunately, drill rig controls do not display weight on bit but instead display feed cylinder pressure.

The weight on bit or force can easily be found by the following "off bottom" method:

1. Suspend the rods with the hydraulic system in the lowering position.
   
   
2. With the drilling motor running at a drill rotation, note the reading on the cylinder feed pressure gauge. This is approximately equal to the hydraulic pump pressure plus the weight of the rods in terms of hydraulic pressure. This is called the “off bottom” pressure.
   
   
3. Rotate the rods and feed them down by opening the restrictor valve. As the bit touches bottom, part of the weight of the rods is supported on the bit. This action is indicated by a decrease in the gauge reading. The difference in the gauge readings is the pressure applied to the bit.
   
   
4. The pressure applied to the bit multiplied by the area of the hydraulic cylinders gives the force or weight on bit.
   
   
5. The bit torque can be measured in a similar fashion by comparing the “off bottom” hydraulic pressure of the rotation unit to the hydraulic pressure while drilling.

Torque generated by the bit is a function of sharpness of the bit and weight on bit, and results from the diamonds cutting the formation. As such, torque should be viewed as beneficial and an indication of drilling effectiveness. Minimum torque occurs just after bit sharpening has completed and as bit weight is reduced. Maximum bit torque occurs during bit sharpening due to the bit matrix coming into contact with the rock. A simultaneous decrease of torque and penetration rate indicates that the bit is polishing and needs to be sharpened. Torque increases due to sharpening should only be a concern in lost circulation or when sharpening requires water restriction. Bits with large diamonds can drop or stall RPM when sharpening. If RPM drops during sharpening then a lower gear or speed should be used to increase available torque.

Decreasing torque and penetration rate indicates bit polishing.

Maximum bit torque occurs during bit sharpening. Only be concerned with torque rise when restricting water or in lost circulation.

Fluctuation in torque, particularly during sharpening is caused by unstable rock fragmentation and/or insufficient rock penetration. Weight on bit needs to be maintained to establish secondary fracturing and stable cutting.

If the head stalls under normal operation, then reduce speed to produce more torque and maintain steady rotation.

Bits with large diamonds can drop or stall RPM when sharpening. If RPM drops during sharpening, then a lower gear or speed should be used to increase available torque.

The cutting rate varies as a result of weight on bit, sharpness, bit formula, and ground conditions. Typical penetration rates vary anywhere from 2 ipm to 12 ipm depending on bit formula and formation. As formations become harder, the penetration rate should be reduced to achieve good bit life. In extremely broken, hard ground, drill at half RPM and weight on bit sufficient to reach 1 to 2 ipm (3 to 5 cpm).

Penetration rates vary anywhere from 2 ipm (5 cpm) to 12 ipm (30 cpm) based on bit
and formation.

In extremely broken, hard, ground, run at half RPM and weight on bit sufficient to
reach 1 to 2 ipm.

The penetration rate to prevent polishing mode may be higher in large diamond bits.

The flow of drilling fluid in the drill hole serves many purposes including the essential cooling of the diamonds, removal of cuttings, and attainment of good bit life. High penetration rates require additional flow to keep cuttings off the bit face, as do higher rotation rates. There is no maximum water flow rate, though at high-flow rates, the bit can be lifted off the rock face, causing it to polish. Free-cutting bits obtain maximum life and penetration using plenty of water.

High penetration and/or rotation rates require additional flow.

There is no maximum water flow rate. At high pressures, the bit can be lifted off the rock face, causing it to polish.

Free-cutting bits obtain maximum life and penetration using plenty of water.

The positive displacement pumps typically used on drill rigs pump water in proportion to how fast they are spinning; the faster they spin the more they pump. The amount of water pumped will be nearly the same over a very large pressure range and for this reason, water pressure does not tell the driller anything about how much water is flowing. For a driller to calculate water flow, they should measure the water pump shaft rpm with a tachometer, and then compare the measured shaft speed with the max speed listed on the nameplate. If the shaft speed is half of the max speed then the water pumped will be half of the listed flow at max speed. The other method is to disconnect the outlet hose and run it to a 5 gallon or 20-liter bucket and time how long it takes to fill. The flow rate is the time in seconds divided by 60 multiplied by either 5 gallons or 20 Liters.

FMC LO918 Nameplate, Max Speed: 625 rpm Output Flow: 20.2 GPM Measured rpm of 240 rpm. Output flow is equal to 240 rpm/625 rpm X 20.2 GPM = 7.5 GPM.

Sharpening, also known as stripping, is the act of conditioning the bit to regain or improve penetration rate. Sharpening of the bit occurs when sufficient weight is applied to create contact between the supporting matrix and the rock. The friction on the matrix removes it and exposes new diamonds. Sharpening is necessary when a new bit is started, if too low a bit has been selected for the rock type or if an impregnated bit has been allowed to slow down and polish. Active sharpening should be done as little as necessary because it reduces bit life.

Add WOB until torque rises, once penetration rate increases, reduce WOB to maintain desired penetration rate.

Reduce RPM by 1/2, wait until torque and penetration rate rises. Return speed to normal operation.

If 1 and 2 are insufficient (up-holes, underpowered rigs, or too low a series bit), reduce
RPM by 1/2 and reduce water flow. Wait until torque and penetration rate rises. Return
speed and water flow to normal operation.

Large diamond bits have a greater rise in torque on initial sharpening. WOB needs to be held until penetration rate increases. Reduce WOB to maintain desired penetration rate once sharp.

If frequent sharpening is required, a higher series bit formula should be selected. Under no circumstances should any acid be used for sharpening a Boart Longyear impregnated bit. Also, shutting off the water flow while drilling and waiting for the bit to "bite", is not recommended by Boart Longyear as a method of sharpening due to the likelihood of burning in the bit.

On the inaugural episode of the INSITE Podcast I sit down with Bob Corona, Design Engineer – Diamond Products, to talk about how being a chemist is akin to being a chef, why building a relationship with your end users is important, and how learning from your mistakes can be your biggest ally. 

This episode coincides with the recent release of Boart Longyear’s new line of Longyear diamond bits. More information about the diamond bits can be found here.

We would love to hear your questions and comments below. Thank you for listening and be sure to share this episode on LinkedIn, Facebook, or Twitter.