How to Compare Cutting Speeds of Thread Button Bits

On a bustling construction site or deep within a mining operation, the difference between meeting a deadline and falling behind often comes down to the tools you use. When it comes to rock drilling, few tools are as critical as the thread button bit—a workhorse designed to bite into stone, concrete, and mineral deposits with precision. But with so many options on the market—from taper button bits to R32 thread button bits—how do you determine which one will drill faster? Comparing cutting speeds isn't just about picking the "speediest" bit; it's about understanding how design, material, and application intersect to deliver optimal performance. In this guide, we'll break down the process step by step, helping you make informed decisions that save time, reduce costs, and keep your projects on track.

What Are Thread Button Bits, Anyway?

Before diving into cutting speeds, let's clarify what a thread button bit is. As a staple in the rock drilling tool family, this bit features a steel body with small, raised "buttons" made from ultra-hard materials—most commonly tungsten carbide—affixed to its cutting face. These buttons are arranged in patterns (often circular or spiral) to distribute pressure evenly as the bit rotates. The "thread" in the name refers to the threaded connection at the shank, which allows the bit to attach securely to drill rods or rigs.

Thread button bits come in various designs to tackle different tasks. For example, a taper button bit has buttons with a conical shape, ideal for penetrating hard rock, while an R32 thread button bit refers to a specific thread size (32mm) commonly used in medium-duty drilling. The choice between them depends on factors like rock hardness, drilling depth, and the type of rig you're using. But at the end of the day, their primary job is the same: to cut through rock efficiently, and cutting speed is the metric that defines "efficient."

Key Factors That Influence Cutting Speed

Cutting speed, measured in meters per hour (m/h) or feet per minute (ft/min), is the distance a bit drills into rock over a given time. But it's not a fixed number—several variables can make the same bit drill twice as fast in one scenario and crawl in another. Let's break down the most critical factors:

1. Rock Hardness: The Unseen Opponent

Rock is the bit's greatest adversary, and its hardness directly dictates how quickly a bit can cut. Geologists measure hardness using the Mohs scale (1 = soft talc, 10 = diamond), but for drilling, engineers often use the Protodyakonov Rock Mass Strength (PRMS) scale, which rates rock from "very weak" (0.3) to "extremely strong" (20+). A thread button bit drilling through soft sandstone (PRMS 2–4) will zip along at 30–50 m/h, while the same bit in granite (PRMS 15–20) might struggle to hit 5–10 m/h. Always assess your rock type first—ignoring this is like racing a sports car on a gravel road and wondering why it's slow.

2. Bit Design: Buttons, Spacing, and Shape

Not all thread button bits are created equal. The arrangement and design of the tungsten carbide buttons play a huge role in cutting speed. Bits with more buttons (e.g., 9 buttons vs. 6) can distribute cutting force over a larger area, reducing wear and increasing speed— but only if the spacing is right . Buttons packed too tightly can trap rock cuttings, slowing progress, while gaps that are too wide leave uneven stress on individual buttons. Shape matters too: spherical buttons are great for general-purpose drilling, while chisel-shaped buttons excel in hard, abrasive rock. Even the thread type matters—an R32 thread button bit, with its standardized 32mm connection, ensures a secure fit to the drill rod, minimizing vibration that would otherwise sap speed.

3. Rotation Speed and Thrust: Power vs. Control

Your drill rig's settings are just as important as the bit itself. Rotation speed (RPM) refers to how fast the bit spins, while thrust is the downward force applied to push the bit into the rock. It's a delicate balance: too much RPM and the buttons may "skid" over the rock instead of biting; too little thrust and the bit won't penetrate deeply enough. For example, a taper button bit in limestone (medium hardness) might perform best at 60–80 RPM with 5–8 kN of thrust, while a harder rock like basalt might need slower RPM (40–50) but higher thrust (10–12 kN) to keep the buttons engaged.

4. Flushing: Clearing the Way

Ever tried digging a hole in wet sand with a shovel that's clogged with dirt? That's what happens when a thread button bit doesn't have proper flushing. Flushing—using water or air to clear rock cuttings from the drill hole—prevents debris from building up between the buttons, which would slow cutting and increase wear. A bit with poor flushing channels might drill fast initially but bog down after a few meters, while a well-designed bit with wide, angled channels will maintain speed by keeping the cutting face clean.

5. Wear and Tear: The Cost of Speed

Cutting speed isn't just about how fast you drill now —it's about how fast you can drill consistently . Tungsten carbide buttons are tough, but they wear down over time, especially in abrasive rock like sandstone. A bit that starts at 40 m/h but wears out after 50 meters (needing replacement) might be less efficient than a slower bit (30 m/h) that lasts 200 meters. When comparing speeds, always factor in "cost per meter drilled" to avoid false economies.

Measuring Cutting Speed: Tools and Techniques

To compare cutting speeds accurately, you need reliable data. Here's how to measure it:

Tools You'll Need

• Drill Rig Monitor: Most modern rigs have built-in screens that track RPM, thrust, and depth in real time—this is your best source of data.
• Stopwatch: For older rigs, a simple stopwatch works. Start timing when the bit touches the rock and stop when it reaches a target depth (e.g., 5 meters).
• Depth Gauge: A steel tape or digital depth meter to confirm the hole depth, ensuring accuracy.
• Rock Sampling Kit: Collect rock chips to test hardness later (using a Mohs pick or PRMS tester).

The Controlled Test Method

The only way to compare two bits fairly is to test them under identical conditions. Here's a step-by-step approach:

1. Choose a Test Site: Pick a location with uniform rock (no sudden changes from granite to shale) and mark a 10–20 meter section for drilling.
2. Set Rig Parameters: Lock in RPM, thrust, and flushing pressure. For example, 70 RPM, 7 kN thrust, and 100 psi air pressure. Keep these exactly the same for both bits.
3. Test Bit A: Drill a 5-meter hole, recording start/end times and final depth. Repeat 3–5 times to account for minor variations.
4. Test Bit B: Swap in the second bit (e.g., a taper button bit vs. an R32 thread button bit) and repeat the process in the same rock.
5. Calculate Average Speed: For each bit, divide total depth by total time (e.g., 25 meters drilled in 50 minutes = 30 m/h average).
6. Check Wear: After testing, inspect the buttons for chipping or flattening. Severe wear means the bit might not sustain speed in long-term use.

Pro tip: If you can't test on-site, many manufacturers provide "speed charts" based on lab testing. While these are helpful, always cross-reference with real-world data—lab conditions (perfect rock, brand-new rigs) rarely match job sites.

Step-by-Step Guide to Comparing Cutting Speeds

Now that you know what influences speed and how to measure it, let's walk through comparing two common bits: a standard taper button bit and an R32 thread button bit, both designed for medium-hard rock (e.g., limestone, PRMS 6–8).

Step 1: Define Your Application

Start by clarifying the job: Are you drilling blast holes in a quarry, or installing anchor bolts for a bridge? For this example, let's say it's a quarry operation needing to drill 100mm diameter holes to a depth of 15 meters, 50 holes per day. Speed is critical, but so is durability—stopping to change bits every hour kills productivity.

Step 2: Assess the Rock

The quarry's limestone has a PRMS rating of 7—medium-hard, with occasional quartz veins (abrasive). This means we need a bit that balances cutting speed with resistance to wear. Tungsten carbide buttons are a must here, as softer materials would wear too quickly.

Step 3: Gather Bit Specs

Let's compare two candidates:

• Bit A: Taper Button Bit – 9 buttons (spherical shape), steel body, 100mm diameter, taper shank (no thread).
• Bit B: R32 Thread Button Bit – 12 buttons (chisel-shaped), tungsten carbide buttons, 100mm diameter, R32 thread connection.

Step 4: Run Controlled Tests

Using the same drill rig, set RPM to 65 and thrust to 8 kN. Drill 5 holes with each bit, recording time and depth. Here are the results:

At first glance, Bit B (R32 thread button bit) is faster—32.1 m/h vs. 22.5 m/h. But let's dig deeper.

Step 5: Analyze Wear and Longevity

After drilling 25 meters, inspect the buttons: Bit A's buttons are slightly flattened, while Bit B's chisel-shaped buttons show minimal wear. Why? The R32 bit has more buttons (12 vs. 9), distributing wear, and its thread connection reduces vibration, which causes uneven button damage. To test longevity, we run both bits until they can't drill faster than 10 m/h. Bit A fails after 80 meters; Bit B lasts 200 meters.

Step 6: Calculate Cost Per Meter

Assume Bit A costs $50 and Bit B costs $80. For 200 meters of drilling:

• Bit A: 200m / 80m per bit = 2.5 bits needed → Total cost: 2.5 x $50 = $125
• Bit B: 200m / 200m per bit = 1 bit needed → Total cost: $80

Even though Bit B is pricier upfront, it's cheaper per meter and faster—making it the better choice for the quarry.

Real-World Scenarios: When Speed Isn't Everything

While the R32 thread button bit outperformed the taper button bit in our quarry example, there are cases where a slower bit might be better. Let's look at two scenarios:

Scenario 1: Hard, Abrasive Rock (Granite, PRMS 18)

In granite, a high-speed bit with sharp, narrow buttons might "burn out" quickly as the buttons wear down. Instead, a slower bit with larger, rounded tungsten carbide buttons (e.g., a 7-button taper button bit) will drill at 8–10 m/h but last 3x longer, reducing downtime for replacements.

Scenario 2: Soft, Clayey Rock (Shale, PRMS 2)

Here, speed is less about the bit and more about flushing. A thread button bit with wide channels to clear clay cuttings will drill faster (40–50 m/h) than a "fast" bit with narrow channels that clogs up. In soft rock, prioritize flushing design over button count.

Common Mistakes to Avoid

Even with careful testing, it's easy to misinterpret data. Watch out for these pitfalls:

Mistake 1: Ignoring Rock Variability

Drilling 5 holes in a "soft" section and assuming the bit will perform the same in a harder layer nearby is a recipe for disappointment. Always test in multiple areas of your site to account for rock variability.

Mistake 2: Comparing Apples to Oranges

Never compare a bit tested on a 500-horsepower rig with one tested on a 200-horsepower rig. Rig power, RPM, and thrust must be identical for a fair comparison.

Mistake 3: Fixating on "Top Speed"

A bit that hits 60 m/h in the first meter but slows to 10 m/h by the fifth is worse than a steady 30 m/h bit. Always calculate average speed over the entire hole depth, not just the start.

Mistake 4: Forgetting Operator Skill

An experienced operator who adjusts RPM and thrust on the fly can make a "slow" bit drill faster than an inexperienced operator with a high-performance bit. If testing with different operators, factor in their skill levels.

Conclusion: Speed with Sense

Comparing cutting speeds of thread button bits isn't a one-size-fits-all process. It requires understanding your rock, your rig, and your project goals—and balancing speed with durability, cost, and real-world conditions. Whether you're choosing between a taper button bit, an R32 thread button bit, or any other rock drilling tool, the key is to test methodically, analyze data thoroughly, and prioritize long-term efficiency over short-term speed. By doing so, you'll ensure your bits work as hard as your team does—turning rock into results, one meter at a time.