Product Overview
RockHound’s R28 Threaded Button Bits are purpose-built for underground drifting and tunneling operations where consistent penetration rate, hole straightness, and bit longevity are non-negotiable. Engineered to the R28 (1-1/8″) thread standard, these bits integrate seamlessly into a complete Top Hammer drill string — from shank adapter through coupling sleeve and drifter rod — delivering efficient energy transfer right to the rock face.
The bit body is precision-forged from 45CrNiMoVa high-alloy steel, offering superior fatigue resistance under high-frequency percussive impact. Cutting inserts are manufactured from YK05 tungsten carbide, a grade selected for its balanced hardness and toughness in abrasive hard-rock formations.
Key Features
- 45CrNiMoVa Alloy Steel Body — Forged for fatigue strength and shock absorption under continuous percussive loading. Resists body washing and shank cracking in wet flushing conditions.
- YK05 Tungsten Carbide Buttons — Premium carbide grade offering high wear resistance and transverse rupture strength — extending bit life in granite, quartzite, and other abrasive formations.
- Dual Gauge Button Angle Options — 30° & 35° — 30° gauge angle suits harder, more competent rock where bit stability is critical. 35° gauge angle improves self-sharpening behavior and debris clearance in medium-hard formations.
- Optimized Flushing Channel Design — Strategic flushing holes ensure aggressive cuttings evacuation, reducing regrinding frequency and preventing heat-induced carbide damage.
- Full R28 System Compatibility — Directly compatible with R28 drifter rods, coupling sleeves, and shank adapters — no adapters or conversion fittings required.
Technical Specifications
All product codes and dimensions sourced from manufacturer engineering data sheets.
- Thread Standard: R28 (1-1/8″)
- Button Material: YK05 Tungsten Carbide
- Body Material: 45CrNiMoVa Alloy Steel
R28 Drill String System Compatibility
The R28 button bit is the terminal component in a matched Top Hammer drill string. A complete R28 system consists of:
- Shank Adapter — Transfers rotary and percussive energy from the drifter/rock drill
- Coupling Sleeve — Joins extension rods with zero thread misalignment
- Drifter Rod — Transmits impact energy down the hole; available in multiple lengths
- Button Bit — Breaks and fragments rock at the face
⚠️ System Note: All R28 components must share the same thread form and pitch. Mixing thread standards (e.g., R25, R32) will result in thread galling, energy loss, and component failure.
Applications
R28 threaded button bits are the industry benchmark for small-diameter percussive drilling across the following sectors:
- Underground Mining — Face drifting, cross-cutting, and development headings in hard-rock mines
- Tunneling & Civil Engineering — Drill-and-blast face drilling in road, rail, and hydropower tunnels
- Rock Bolting — Systematic roof and rib support drilling in underground excavations
- Quarrying — Production drilling and secondary breakage in dimension stone and aggregate operations
- Construction Anchoring — Ground anchor and rock bolt installation in hard to medium-hard formations
Recommended Rock Hardness: 80–250 MPa UCS (Medium-hard to Very Hard)
How to Select the Right R28 Button Bit
By Rock Type
| Rock Condition | Recommended Button Profile | Recommended Gauge Angle |
|---|---|---|
| Hard & Highly Abrasive (granite, quartzite) | Spherical (Dome) | 35° |
| Medium-Hard (limestone, sandstone) | Ballistic | 35° |
| Very Hard, Competent | Spherical (Dome) | 30° |
By Hole Diameter
- 38 mm — Narrow drift development, rock bolting pilot holes
- 41 mm — Standard production drifting and tunneling
- 43 mm — Larger blast-hole patterns requiring increased burden capacity
Button Profile Guide
- Spherical (Dome) Buttons — Higher wear resistance; preferred in abrasive formations where regrinding intervals must be extended
- Ballistic Buttons — Sharper tip geometry for higher initial penetration rate (ROP) in softer, less abrasive rock
Related Reading:How to Choose the Right Top Hammer Drill Bits
Maintenance & Service Life Optimization
Proper maintenance directly determines your cost-per-meter drilling performance.
1. Regrind Before Flat Wear Exceeds 1/3 of Button Diameter Waiting until buttons are fully flattened causes body washing — irreversible erosion of the steel around the carbide insert seat — which voids the bit entirely.
2. Thread Greasing is Non-Negotiable Apply approved thread paste to all R28 male threads before coupling. Dry threads cause cold welding (galling), making uncoupling impossible underground and damaging coupling sleeves.
3. Monitor Flushing Pressure Insufficient water or air flushing volume leads to chip re-grinding beneath the face, dramatically increasing carbide wear rates and thermal stress cracking.
4. Inspect After Every Shift Check for: asymmetric button wear (indicates bit rotation issues), cracked carbide inserts (impact overload), and thread form integrity before re-deployment.
5. Dry, Sheltered Storage R28 threads corrode rapidly in humid environments. Store bits on racks, thread-ends capped, in a climate-controlled container or tool store.
Related Readings:Top Hammer Button Bit: How It Works, Uses & Maintenance
Why Choose RockHound
- Full R28 System Supply — Bits, rods, coupling sleeves, and shank adapters from a single source
- Verified Material Specifications — 45CrNiMoVa body steel and YK05 carbide, independently traceable
- Technical Support — Application engineering available for bit selection and drill parameter optimization
- Fast Global Dispatch — Standard stock items shipped within 3 business days
Related Production
R32-H28-R28 Threaded Drifter Rod For Tunneling
RockHound R32-H28-R28 Threaded Drifter Rod is a high-performance top hammer drilling component purpose-built for underground tunneling, drifting, and development drilling.
FAQ
R28 button bits are designed for use with R28 (1-1/8") threaded drifter rods and coupling sleeves. The full drill string — shank adapter, coupling sleeve, rod, and bit — must all carry the R28 thread standard.
The gauge button angle affects the balance between bit stability and self-sharpening. A 30° angle keeps gauge buttons more radially oriented, improving hole diameter retention in hard rock. A 35° angle promotes better carbide re-exposure as the button wears, extending effective cutting life in medium-hard formations.
Spherical (dome) buttons generally offer longer service life in highly abrasive rock due to a larger wear-flat area before performance degrades. Ballistic buttons deliver faster penetration in softer formations but wear faster in abrasive conditions.
Yes. Button bits should be reground using a dedicated carbide button grinder matched to the button diameter (9 mm or 10 mm in these configurations). Regrinding restores the button dome profile, recovering 60–80% of original penetration rate.
Service life varies significantly by rock hardness, flushing efficiency, and drill rig settings. In medium-hard rock with correct flushing, 300–600 blasthole meters per bit is achievable. In hard abrasive formations, 100–200 meters is typical without regrinding.
45CrNiMoVa is a high-strength alloy steel known for its exceptional fatigue resistance and toughness. In drifting and tunneling, bits face intense repetitive impact; this specific steel grade prevents body breakage and "plugging" (carbide loss) even under high-pressure drilling conditions.
Yes. YK05 is a premium grade of tungsten carbide that offers an ideal balance between hardness and fracture toughness. It is specifically designed to resist abrasive wear in medium-to-hard rock while maintaining the structural integrity of the button tips.
Yes. While our standard stock features Spherical buttons for maximum durability, we provide customization options for Ballistic or Conical buttons for clients working in softer formations who require higher ROP (Rate of Penetration).
Lifespan varies based on rock abrasiveness and drilling pressure. However, by using 45CrNiMoVa + YK05, our bits typically offer a 15-20% longer service life compared to standard carbon steel bits, provided that regular sharpening and maintenance protocols are followed.