When the operator applies insufficient feed thrust, the drill bit is not pressed firmly against solid rock when the percussion piston strikes. Because the rock face provides zero acoustic resistance, the compressive stress wave reflects from the free bit boundary as an inverted, high-amplitude tensile wave travelling back up the rod. Carburized drill steel has high compressive strength but poor tensile fatigue endurance. Rattling without adequate feed causes rapid thread stripping, shank adapter fracture, and catastrophic coupling breakage within minutes. Maintain feed thrust above $(1.3 - 1.6) imes P_{imp} / v_p$.

Excessive feed thrust forces the bit into the rock beyond the natural crushing depth per blow. This jams the carbide buttons into fracture craters, spiking rotational torque and causing rotation motors to stall. The extreme column load induces elastic buckling in the drill string, causing borehole deviation (>5° off axis), severe bending stress on male/female rod threads, and premature gauge button wear on the perimeter.

If compressor output is undersized or air loss occurs through fractured ground, the upward annular air velocity drops below 15 m/s (3,000 ft/min). Heavy rock cuttings cannot be lifted to the surface and fall back down the hole. The bit is forced to re-crush existing cuttings into fine powder rather than fracturing virgin rock. This cuts penetration rate by 50% to 70%, generates extreme friction that overheats carbide inserts (causing thermal micro-cracking / snake skin), and eventually wedges the drill string in a packed hole.

Spinning the rotation motor too fast relative to percussion frequency (indexing angle $>18^circ$ per blow) leaves tall, unbroken rock ridges between consecutive button strike craters. When the carbide buttons subsequently hit the steep sides of these rock ridges on the next blow, they experience destructive lateral shear forces rather than pure axial compression. Tungsten carbide buttons readily fracture in shear, leading to pop-out failures and ruined drill bits.

Hydraulic drifters rely on high-pressure nitrogen gas accumulator bladders to absorb the reflected hydraulic pressure spikes generated when the spool valve cuts off flow at 50 to 80 Hz. If nitrogen pre-charge pressure is neglected or the elastomer bladder ruptures, water-hammer pressure spikes (>350 bar) propagate through the hydraulic pump, blowing pump swashplates, tearing hose crimps, and eroding valve sleeves within hours. Check accumulator pre-charge weekly.