An electric percussion rock drill uses motor power to produce repeated impacts at the tool. In the air-cushion arrangement illustrated here, a crank-driven piston compresses air behind a separate striker. The striker hits a beat piece, which transmits the blow to the bit. Rotary drilling also indexes the bit through a separate rotary drive.
Electric Rock Drill Interactive Calculator
Compare measured blow energy and rate while following the crank, piston, air cushion, striker and bit. Percussion power is an energy-rate calculation, not a prediction of drilling speed.
Equation Used
- Constant entered energy and blow rate.
- No penetration-rate or bit-life model.
- Rigid crank/rod geometry; schematic air-cushion and contact timing.
- Rotary transmission outside the sectional view.
Animation slowed 100×. Striker and bit indexing are a prescribed explanatory sequence, not a pressure/contact simulation.
Follow the moving parts in the cutaway
The blue housing and cylinder stay fixed. The crank rotates inside its bearing and its connecting rod moves the blue drive piston. The cyan chamber between piston and striker changes length. The orange striker has no connecting rod: the air cushion transfers energy to it. At the forward end it reaches the grey beat piece, which contacts the tool shank.
The exterior handle, barrel, chuck and fluted bit show the complete tool around the working parts. A section through the piston train makes the separate components visible. The rotary-drive gears are outside this sectional view; a slow bit index indicates their separate function rather than an inferred gear ratio.
The crank and connecting rod satisfy their rigid-length geometry. Striker, recoil and bit-index timing are an explicitly prescribed explanatory sequence. They are not calculated from gas pressure or rock contact, and no striker speed or impact force is inferred. The displayed cycle is slowed 100 times relative to the entered blow interval.
Compare percussion energy rates
Enter measured or consistently rated energy per blow and blows per minute. The calculator reports mean percussion power, frequency, total energy per minute and the interval between blows. Keep the energy measurement point consistent when comparing tools: striker kinetic energy and energy delivered to a test fixture are not automatically identical.
These quantities describe the percussion energy stream. They do not predict penetration rate, hole quality, bit life, feed force, motor input or generator size. Those depend on the complete machine, bit, rock and operating conditions.
Power from discrete impacts
For energy E in joules per blow and rate n in blows per minute, frequency f=n/60 Hz. Mean percussion power is P=Ef=En/60 W. Energy delivered at that same measurement point over one minute is En/1000 kJ. Time between blows is 60000/n milliseconds.
This is an average energy rate, not instantaneous impact power or force. Contact duration and deformation would be needed to describe an individual force pulse. Electrical input power additionally includes motor, gear, air-cushion and other losses.
The illustrative crank radius is 35 drawing units and connecting rod length 110. With crank angle θ, its slider coordinate relative to the crank center is x=35 cos θ+√(110²−35² sin²θ). Those drawing units are not tool manufacturing dimensions.
Example: 15 J at 2,500 blows per minute
The blow frequency is 41.667 Hz and the interval is 24 ms. Mean percussion power is 15×2500/60=625 W, with 37.5 kJ of percussion energy per minute at the specified measurement point.
Changing to 30 J at the same rate doubles the power to 1,250 W. Changing only the rate to 4,500 blows/min gives 75 Hz, a 13.333 ms interval and 1,125 W at 15 J. Neither comparison determines which tool will drill a particular rock faster.
What this model leaves out
The piston train is a simplified generic air-cushion arrangement. Seals, ventilation and idle-strike prevention ports, clutches and rotary-drive gearing are not simulated. The impact is briefly highlighted to make contact visible; it is not a measured contact-time waveform.
Historical electric drills also used directly energized electromagnetic plungers. Those differ from the motor-and-air-cushion construction shown here. Modern breakers, rotary hammers, hydraulic drills and core drills should not be treated as interchangeable versions of one mechanism.
Electric rock drill questions
Is percussion power the same as electrical input power?
No. It is the energy per blow multiplied by the blow frequency at the stated measurement point. Electrical input also supplies losses and any other driven functions.
Why is the striker not connected to the rod?
The rod drives the piston. Air between that piston and the separate striker transfers the force. Joining the striker directly to the rod would depict a different mechanism.
Does twice the power mean twice the drilling speed?
Not necessarily. Rock, bit geometry, rotation, flushing, feed and energy transfer all influence penetration.
Why is the displayed motion slow?
At the default 2,500 blows/min, real blows are only 24 ms apart. The animation uses a 100-times time expansion so each stage can be inspected.
Primary mechanism references
Bosch US7121359B2, drilling hammer, figure 1 and the accompanying description, documents the motor-driven crank, connecting rod, piston train and separate rotary transmission. The simplified section explains the component arrangement; it is not a product manufacturing drawing.
Bosch DE2438938A1, motor-driven hammer describes a crank-driven piston, air-cushion-driven striker and an intermediate impact member. The animation shows the piston, air cushion and separate striker.
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