Epiroc Pit Viper 351
A rotary blasthole drill rig built to bore the deep, wide holes mines fill with explosives to fracture rock ahead of loading — one of the largest rotary drills in regular production.
Mast height, approximated from single-pass drill depth: 19.8 m — about 11× an average adult's height (1.8 m). The machine is always drawn at the same size here; the human figure is what actually scales.
01Overview
A rotary blasthole drill rig built to bore the deep, wide holes mines fill with explosives to fracture rock ahead of loading — one of the largest rotary drills in regular production.
02Purpose
Exists purely to prepare rock for blasting — drilling the holes a mine later fills with explosives, a job that has to finish before any of the site's excavators can start.
03Historical Development
Rotary blasthole drilling replaced older percussion drilling methods at large open-pit mines because rotary bits, under enough downward force, cut faster and more consistently through hard rock at the diameters mine blasting patterns actually need. Atlas Copco (now Epiroc, after the 2018 split) developed the Pit Viper line specifically for this large-diameter, high-productivity segment, with the 351 sitting near the top of the range.
04Core Components
- Rotary headApplies both downward force (bit load) and rotation to the drill string simultaneously, the two things a tricone bit needs to cut rock efficiently.
- Tricone drill bitThree cone-shaped cutting elements that roll and crush rock as the string rotates, standard for large-diameter blasthole drilling.
- MastA tall vertical structure holding the drill string, tall enough to handle a full single-pass depth of nearly 20 metres without adding sections.
- Air compressor systemDelivers high-volume compressed air down the drill string to clear cuttings from the hole and cool the bit.
05How It Works
The rotary head clamps onto the drill string and applies both rotation and substantial downward force — up to 56.7 tonnes of bit load — driving the tricone bit's three rolling cutters into the rock face. Compressed air, pumped down through the hollow drill string at up to 3,800 cubic feet per minute, escapes through the bit and carries rock cuttings back up the annulus around the drill string and out of the hole, keeping the bit clear and cool as it advances. Once a hole reaches its target depth, it's charged with explosives as part of a wider blast pattern designed to fracture rock for loading by shovels or excavators.
06Engineering Principles
The rotary head must deliver sustained torque to keep three rolling cutters biting into hard rock without stalling, all while also pressing down with tens of tonnes of bit load.
HydraulicsHydraulic CylindersMast raising, drill-string clamping, and rod-handling functions are all hydraulically actuated.
Power TransmissionBearingsThe tricone bit's own rolling cutters ride on sealed bearings that must survive continuous rock-crushing loads at the very tip of the drill string, in the harshest environment on the whole machine.
07Performance Characteristics
| Hole diameter range | 270 – 406 mm |
| Single-pass depth | 19.8 m |
| Multi-pass depth | up to 41.1 m |
| Bit load capacity | 56.7 t |
| Air capacity | 3,800 cfm at 110 psi |
08Notable Examples
- Large open-pit metal and coal mines worldwidePit Viper-class rigs drill blast patterns across benches ahead of shovel-and-truck loading fleets.
09Interesting Facts
- The pattern and depth of every hole a rig like this drills is planned in advance as part of a full blast design — drilling isn't improvised, it follows an engineered grid.
- Bit load, not rotation speed, is usually the limiting factor in tricone drilling productivity: more downward force generally cuts rock faster than spinning the bit harder.
- A single rig can drill dozens of holes in a shift, each one eventually packed with explosive and tied into a single, precisely timed blast.