Xi'an Heaven Abundant Mining Equipment CO.,LTD
Tunnel face drilling is one of the most demanding applications in underground construction. Whether you are working on a highway tunnel, a railway passage, or a hydroelectric project, the quality of your drill bit directly determines how fast you advance and how often you stop to ｒｅｐｌａｃｅ worn tools. Among the various options available, the taper button bit has become the go-to choice for contractors and mining crews who need reliable penetration in hard rock formations.
A taper button bit is a percussive drilling tool that connects to a tapered drill rod through a friction-based interference fit. The bit has a conical socket at its rear end that mates with the matching taper on the rod — typically at 7°, 11°, or 12° angles. No threads, no mechanical fasteners. The impact energy from the rock drill travels through the rod, into the bit body, and then to the tungsten carbide buttons on the bit face. Each button strikes the rock with concentrated force over a tiny contact area, generating stress levels that exceed the compressive strength of the rock and causing it to fracture.
After each impact, the bit rotates slightly, chipping away the freshly cracked surface and clearing the cuttings with flushing air or water. This repeat cycle of point-contact crushing, crack propagation, and chip ejection is what makes the taper button bit so effective in hard, abrasive ground. Unlike chisel-type bits, the omnidirectional buttons maintain consistent rock-breaking performance at every rotation angle.
Tunnel face drilling presents a unique set of challenges. The working space is confined, the rock conditions can change abruptly from one blast round to the next, and downtime for bit changes is expensive because it halts the entire excavation cycle. Taper button bits address these challenges in several ways.
First, the taper connection allows for rapid bit changes. A few hammer taps on the bit skirt are all it takes to seat or release the bit from the rod — no wrenches, no threading, no cross-threading risks. In a tunnel where every minute counts, this quick-change capability adds up to significant time savings over the course of a shift.
Second, the button design handles mixed-face conditions well. Tunnel faces often expose multiple rock types — a band of granite running through sandstone, or a seam of fractured shale crossing the face. The carbide buttons on a taper bit crush through these transitions without the edge chipping or catastrophic failure that can plague cross-type or chisel bits in the same conditions.
Third, taper button bits are available in a wide range of diameters — typically from 28mm to 60mm — making them suitable for everything from small-diameter blast holes to larger boreholes for ventilation or service lines. The same taper rod can drive multiple bit sizes, reducing the inventory of rock drilling tool equipment needed on site.
The profile of the tungsten carbide buttons on the bit face has a direct impact on drilling speed and bit life. Three main profiles are commonly used, and choosing the right one depends on the rock type at the tunnel face.
Hemispherical buttons are the strongest option. With a smooth, rounded tip that distributes impact forces evenly, they resist chipping and fracturing better than any other profile. This makes them the preferred choice for extremely hard rock like granite, basalt, and quartzite. The trade-off is slightly lower penetration speed compared to sharper profiles, but in abrasive formations where bit life is the primary concern, hemispherical buttons deliver the lowest cost per meter drilled.
Conical-ballistic buttons strike a balance between strength and penetration. The tip has a smaller radius of curvature than a full hemisphere, which concentrates impact energy into a smaller area and improves the rate of penetration in hard to medium-hard formations. This profile is widely used in limestone, sandstone, and mixed-face tunnel conditions, and it represents the most versatile choice for general tunneling work.
Parabolic buttons have the sharpest profile and the highest penetration rate but the lowest impact resistance. They are best reserved for soft to medium-hard rock where fast drilling is the priority and the risk of button fracture is low.
Beyond the button profile, the overall face geometry of the bit influences performance in tunnel drilling. A concave face design centers the bit in the hole and provides excellent hole deviation control, which is particularly important when drilling blast holes that must follow a precise pattern. A convex face, on the other hand, offers the highest resistance to steel wash and body wear, making it a good choice in highly abrasive formations where the bit body itself is subject to erosion. Flat face designs represent a middle ground and are often used in homogeneous rock conditions.
For tunnel face drilling specifically, concave face bits tend to be preferred because hole straightness directly affects blast quality. A wandering hole can cause uneven burden, poor fragmentation, and flyrock — all of which slow down the mucking and scaling phases of the tunnel cycle.
The taper angle on the bit must match the rod exactly. The standard angles are 7°, 11°, and 12°, with 7° being the most common for general tunneling work. The 11° and 12° tapers are typically used with larger diameter bits and in applications where a more secure grip is needed. The rod shank dimensions — H19 (19mm hex), H22 (22mm hex), and H25 (25mm hex) — also need to be matched to the rock drill's chuck size.
A properly matched taper connection transfers impact energy efficiently. If the fit is too loose, energy is lost at the joint and the bit may come off in the hole. If it is too tight, the bit skirt can split under repeated impact. Quality manufacturers control the taper socket machining to tight tolerances and apply surface hardening treatments to extend the service life of the connection.
Both taper and thread button bit designs have their place in tunneling operations. Thread button bits, which use R25, R32, T38, T45, or T51 thread connections, are the better choice for deeper holes, larger diameters, and applications where the bit must stay on the rod reliably — such as drifting and long-hole production drilling. The threaded connection provides a positive mechanical lock that a friction-fit taper cannot match over extended hole lengths.
Taper button bits, however, excel in situations where quick bit changes and lower tooling costs are the priority. For tunnel face drilling where hole depths typically range from 2 to 5 meters and the operator needs to swap bits frequently as they encounter varying rock conditions, the taper system is hard to beat. The bits themselves are less expensive than threaded equivalents, and the taper rods can be reused across multiple bit changes.
Not all taper button bits are built the same. The difference between a bit that lasts 200 meters and one that fails at 50 meters often comes down to three factors: the grade of the cemented carbide, the quality of the brazing, and the precision of the taper socket machining.
The carbide grade matters because it determines how the buttons balance hardness and toughness. For hard, abrasive tunnel rock, a low-cobalt, fine-grained carbide grade provides the wear resistance needed to keep the buttons sharp through multiple blast rounds. The brazing process — whether high-frequency induction or flame brazing — must create a uniform, void-free bond between each button and the bit body. Any gap in the braze joint becomes a failure point under the thousands of high-energy impacts a bit endures during a single shift.
The taper socket itself should be machined to match the rod taper precisely, and the skirt area should receive a zinc coating or similar surface treatment to enhance friction and prevent galling during repeated bit changes.
When sourcing taper button bits, tunnel contractors should look beyond the price-per-bit figure and evaluate the total cost per meter drilled. A cheaper bit that wears out in half the time may end up costing more in downtime, labor, and replacement frequency than a higher-quality bit that delivers consistent performance across multiple shifts.
TY Drill Bits, operating out of Xi'an, China, has been supplying taper button bit products to mining and tunneling contractors worldwide since 2010. The company manufactures taper button bits in diameters from 28mm to 60mm, with all standard taper angles and button profiles available. Each bit is brazed under controlled conditions to ensure consistent carbide retention, and the taper sockets are machined to match standard H19, H22, and H25 rod dimensions. For operations that also require threaded bits for deeper hole applications, TY offers a full range of thread button bits in R25, R32, T38, T45, and T51 connections.
With ISO9001-certified manufacturing processes and a focus on export markets — over 90% of production goes to international customers — TY Drill Bits has built a track record of delivering reliable rock drilling tools to projects across Asia, Africa, South America, and the Middle East. Whether you need a standard catalog item or a custom bit configuration for a specific tunnel geology, the engineering team can match the carbide grade, button profile, and face design to your ground conditions.
The taper button bit remains a mainstay of tunnel face drilling for good reason. Its simple, robust design, quick-change capability, and adaptability to different rock types make it an essential tool in any underground contractor's arsenal. By matching the button profile, face geometry, and carbide grade to the specific rock conditions at the tunnel face, and by sourcing from a manufacturer that controls quality at every stage of production, tunneling crews can drill faster, change bits less often, and keep their projects on schedule.
Email to this supplier
About Us
Products
Contact Us
Privacy statement: Your privacy is very important to Us. Our company promises not to disclose your personal information to any external company with out your explicit permission.
Fill in more information so that we can get in touch with you faster
Privacy statement: Your privacy is very important to Us. Our company promises not to disclose your personal information to any external company with out your explicit permission.
