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 ApplicationBefore choosing rock drilling tools, consider:Rock hardness (soft, medium, or hard)Drilling depthHole diameterDrilling method (manual, pneumatic, or hydraulic drill jumbo)2. Choosing the Right Tapered Drill Bit1.1 Common Types of Tapered Drill BitsTapered 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 BitChisel 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 BitCross 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 BitTaper Cross BitTapered Button Bit3. Choosing the Right Tapered Drill Roda. Rod LengthLength (mm)Application600–800Shallow hole drilling, manual use1200–1600+Efficient for deeper drillingb. Rod DiameterDiameterDescriptionHex22Lighter, for general drillingHex25Stronger, for tough underground drillingc. Match the TaperAlways 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 DrillingDrilling SituationTaper AngleBit TypeRod DiameterSoft to medium rock11° / 12°Cross/ButtonHex22Hard rock or deeper holes7°ButtonHex25Manual drilling, short holes11°CrossHex22Hydraulic drill jumbo use7°ButtonHex255. Final Tips for Drill Jumbo OperatorsChoose high-quality alloy steel rods and bitsMatch taper angles correctly to avoid slippageRegularly inspect for wear to prevent breakageFor underground mining and tunnel work, prefer 7° taper button bits with Hex25 rods on drill jumbosContact Aivyter for Drilling SolutionsNeed 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.