A raise bore machine, often called a raise borer or a raise boring rig, is one of the most powerful and precise pieces of equipment in underground mining and civil tunnelling. It drills a pilot hole from one level to another and then reams it back to full diameter from the bottom up, delivering a finished shaft or raise without a single person ever entering the opening. The technology looks simple in principle, yet the choices around it – capacity, cutter design, ground conditions, maintenance and safety – decide whether a project makes money or burns it. This article walks through the questions engineers, contractors and buyers actually ask, in plain terms, before and during a raise boring project.
A raise boring rig works in two clearly separated stages. In the first stage, a small-diameter pilot bit is rotated and pushed downward from the top (or, in some layouts, upward from the bottom) to drill a slim pilot hole along the designed centreline. This pilot hole is normally 200 to 350 mm in diameter and is drilled with ordinary rotary drilling tools, including drill pipes, stabilizers and a tri-cone or PDC pilot bit. The hole is surveyed as it advances so that the finished raise does not wander off line.
Once the pilot bit breaks through at the far end, the drill string is retrieved and a reamer head is attached at the bottom. The reamer head is pulled upward while the machine rotates the drill string from the top, so the reamer cuts the rock from the bottom towards the surface. Rock cuttings fall to the bottom of the raise, where they can be removed, and the ground ahead is never occupied by men or machines. The finished product is a smooth, circular, full-diameter shaft that needs no blasting, no mucking during the actual ream, and no personnel exposure to a working face.
Conventional raise construction used to mean one of three methods: drilling and blasting from a working face, Alpine miner (roadheader) excavation, or long-hole drilling and benching. All of them expose crews to the excavation face, produce overbreak, and are slow in hard rock. A raise bore machine replaces most of that cycle. The decisive advantages are worth listing because they drive the business case.
The method shines for ventilation raises, ore passes, chutes, escape ways, and pipeline or cable shafts in hard, abrasive, or unstable rock. It becomes less attractive in extremely soft or running ground, where the pilot hole may be difficult to control, and in very shallow or heavily inclined openings that do not justify mobilising a large rig.
A raise boring system is more than the machine sitting on the upper level. It is a chain of equipment that must be matched. The main links are:
A common mistake is to focus only on the rig and ignore the cutter package. In many projects the reamer and its cutters cost as much as or more than the machine, and they decide penetration rate and tool life. Matching the cutter to the rock is therefore as important as choosing the correct borer size.
Sizing a raise borer is driven by four numbers, and they interact with each other. The table below summarises what each parameter means and what pushes it up.
| Parameter | Typical range | What it means and what increases it |
| Reaming diameter | 0.9 m – 6 m+ | The largest diameter the machine and reamer can cut. Larger diameters need higher torque and pull. |
| Hole depth / length | 100 m – 1000 m+ | Total raise length. Depth drives the need for a long drill string and a powerful hoisting/pull system. |
| Pull force | Up to 5000+ kN on large rigs | The upward force that pulls the reamer through the rock. Hard, abrasive and jointed rock demand high pull. |
| Torque | Up to 200+ kNm on large rigs | The rotational force that breaks the rock. Bigger diameters and harder rock raise the torque requirement. |
Two practical rules govern selection. First, the machine’s rated diameter and torque must cover the largest raise on the project with margin, because cutter load grows roughly with diameter squared. Second, the pull force must overcome the rock’s resistance plus the weight of the drill string; underestimating either leads to stalls and cutter damage. It is usually wiser to select a rig one size above the nominal requirement than to run it constantly at its limit.
Once the machine is on site, the three levers an operator controls are rotation speed, pull (thrust) and, for pilot drilling, flushing. Getting them right is the difference between a smooth campaign and a string of broken cutters.
Penetration rate is a function of the cutters biting into the rock at the right load. A good field practice is to track metres per hour, cutter hours per set, and torque draw together. If torque rises sharply while penetration stalls, the cutters are likely dull or the pull is too low; if penetration is high but cutter wear is extreme, speed is probably too high. None of these numbers can be optimised without good instrumentation, so a rig with reliable torque, pull and depth readouts is not a luxury – it is the tool that protects the investment.
Raise boring is reliable, but it is not immune to trouble. The most frequent problems, and their practical fixes, are:
| Problem | Likely cause | Typical remedy |
| Pilot hole deviates off line | Incorrect stabilizer spacing, soft ground, low RPM | Re-survey early, add stabilizers, adjust weight and speed |
| Torque spikes or stalling | Dull reamer cutters, excessive pull, hard ground | Reduce pull, check cutters, change to matching cutter type |
| Slow penetration | Wrong cutter for rock, low pull, worn bits | Match cutters to rock hardness, increase pull within limit |
| Excessive cutter wear | Too high RPM, abrasive rock, poor cooling | Lower speed, upgrade cutters, improve flushing |
| Drill string bending or buckling | Over-pull, inadequate stabilizers | Reduce pull, add stabilizers, inspect string |
| Lost circulation / flushing loss | Fractured ground | Adjust flushing medium, slow pilot drilling, use casing |
The common thread is that most problems trace back to a mismatch between the tooling and the ground, or to running the machine outside its design envelope. A disciplined start-up – recording ground conditions, cutter condition and operating parameters on every shift – usually makes these problems visible before they become expensive failures.
A raise borer works hard and is expensive to repair, so maintenance is scheduled around the drill string and the reamer as much as around the machine itself.
Cutter life is the biggest consumable cost. Keeping a spare cutter set on site, rotating cutters to balance wear, and recording cutter hours per position extend tool life measurably. Downtime in raise boring is rarely cheap, and a small maintenance habit can save a full shift of lost production.
Raise boring is chosen partly for safety, but it still demands strict control. The rules that matter most are:
Modern rigs integrate torque, pull and depth monitoring, alarms and remote control so that the operator stays away from the highest-risk zones. Safety in raise boring is not an add-on; it is designed into the machine, the method and the shift routine.
Buying or renting a raise borer is a major decision. The questions below sort out whether a machine fits the project:
Buyers who answer these honestly before signing usually avoid the two classic mistakes: buying a rig that is technically capable but undersized for the hardest raise, or buying one that is oversized, expensive and idle for most of the year.
The economics of a raise borer are straightforward when the comparison is fair. Conventional sinking carries the recurring cost of a large crew, explosives, mucking, support and rework; raise boring converts most of that into machine time, cutters and a small crew. The payback calculation should weigh:
A useful rule of thumb is to model at least the hardest and the most common raise on the programme, because average numbers hide the decisive case. If the machine is on a mine that will sink many ventilation raises and ore passes over several years, the business case almost always closes. If it is a one-off civil contract, renting with a tooling package may beat owning. Either way, the decision should be made on total cost per metre of finished raise, not on the sticker price of the machine.
A raise bore machine is a proven, safe and fast way to build vertical and steeply inclined shafts, but it rewards preparation. Sizing the rig to the hardest raise, matching cutters to the ground, monitoring torque and pull, maintaining the string and reamer, and asking the right questions before purchase are the habits that turn a powerful machine into a profitable project. For any engineer facing a programme of raises, the numbers, the ground and the support network matter far more than the brand on the machine.
