A Down-The-Hole Drill is called DTH in most drilling terms. The down-the-hole drill is basically a mini jack hammer that screws on the bottom of a drill string. The fast hammer action breaks hard rock into small flakes and dust and is blown clear by the air exhaust from the DTH hammer. The DTH hammer is one of the fastest ways to drill hard rock. Now smaller portable drillcat drilling rigs with DTH hammers can drill as fast as much larger truck rigs with this newer technology.

History

A pneumatic tool is first thought to have been used for rock drilling in 1844. Mr Burton invented a "wind hammer" for boring holes in mines.

Origin of the name

DTH is short for “down-the-hole”. Since the DTH method was originally developed to drill large-diameter holes downwards in surface-drilling applications, its name originated from the fact that the percussion mechanism followed the bit down into the hole. Applications were later found for the DTH method underground, where the direction of drilling is generally upwards instead of downwards.

Technical details

In DTH drilling, the percussion mechanism – commonly called the hammer – is located directly behind the drill bit. The drill pipes transmit the necessary feed force and rotation to hammer and bit plus compressed air or fluids for the hammer and flushing of cuttings. The drill pipes are added to the drill string successively behind the hammer as the hole gets deeper. The piston strikes the impact surface of the bit directly, while the hammer casing gives straight and stable guidance of the drill bit. This means that the impact energy does not have to pass through any joints at all. The impact energy therefore is not lost in joints allowing for much deeper percussion drilling.This is a Great break through for smaller portable water well drilling rigs, that before were limited. The DTH on smaller rigs now can get same results as large heavy truck rigs.

With recent advances in technology DTH hammers and bits can now be operated to run at up to 500Psi, increasing the Rate of Penetration (ROP)^[2]

Uses

DTH drilling is used in the construction industry to produce piles into rock, also water wells, and drilling bores for geothermal ground source heat pumps.

DTH products can be used in the following applications:

Mining- Drill & Blast holes in Open Pit mining, Where the drill operator will drill several holes, then fill with explosives and detonate to lift rock allowing access to ore body RC- Exploration & Pit grade control GW- Geothermal Bore Holes & Waterwells Oil & Gas- Deepwell Bore Holes Construction- Piling, Footings