A Practical Guide to Selecting Tapered Drill Rods and Bits for Underground Drilling

Tapered drill tools are essential for underground mining, tunnel drilling, and quarry operations. Selecting the right tapered drill bit and tapered drill rod can improve your drill jumbo efficiency, extend tool life, and reduce downtime. This guide explains how to choose the best configuration for your rock drilling project.

1. Understand the Drilling Application

Before choosing rock drilling tools, consider:

• Rock hardness (soft, medium, or hard)

• Drilling depth

• Hole diameter

• Drilling method (manual, pneumatic, or hydraulic drill jumbo)2. Choosing the Right Tapered Drill Bit

1.1 Common Types of Tapered Drill Bits

Tapered drill bits are available in several head types designed for different rock formations and drilling machines. The most common taper angles are 7°, 11°, and 12°, with optional taper sizes including 4.8°, 6°, and 9° for special applications.

Chisel Bit

Chisel bits are suitable for lightweight rock drills and drilling holes under 50 mm in diameter, especially in low-hardness rock.
They are widely used in coal, iron, gold, copper, lead-zinc mines, as well as in railway, highway, hydraulic tunnel excavation, and municipal engineering.

Cross Bit

Cross bits are designed for high-powered rock drills and complex formations with fractured or fissured rock layers.
They offer high radial wear resistance, stable performance, and are made with premium steel and carbide for high productivity and cost-efficiency.

Button Bit 

Tapered button bits are ideal for medium-hard rock in both dry and wet drilling operations.
They are extensively used in mining, traffic engineering, hydraulic projects, tunnels, quarrying, and urban infrastructure rock breaking applications.

Chisel Bit

Taper Cross Bit

Tapered Button Bit

3. Choosing the Right Tapered Drill Rod

a. Rod Length

b. Rod Diameter

c. Match the Taper

Always match the taper angle of the rod with the drill bit – typically 7°, 11°, or 12° – to ensure proper energy transmission and tool life.

4. Summary Table for Underground Mining & Tunnel Drilling

5. Final Tips for Drill Jumbo Operators

• Choose high-quality alloy steel rods and bits

• Match taper angles correctly to avoid slippage

• Regularly inspect for wear to prevent breakage

• For underground mining and tunnel work, prefer 7° taper button bits with Hex25 rods on drill jumbos

Contact Aivyter for Drilling Solutions

Need help choosing tapered drill bits and rods for your underground mining project or drill jumbo system?
Our experts at Aivyter will recommend the best configuration for your site.