Short answer
A breaker’s output rests on two simple things: the tool has to meet the material square, and the machine has to press it down enough. Enough means carrying the breaker’s own weight plus a little from the boom; not so much that the machine lifts, not so little that the tool bounces. On angle the rule is stricter: the tool must be perpendicular to the face. A tool set at an angle converts part of every blow into lateral load, and that load goes into the bushing, the shank and the housing. These two settings are the decision every operator, however experienced, repeats hundreds of times a day.
Too little pressure: where blank firing comes from
When a breaker is run before the tool is properly seated, the piston’s energy goes back into the breaker’s own internals instead of into the material. On site this is called blank firing, and it is among the heaviest damage a breaker takes.
Too little pressure is not the only cause of blank firing but it is the most common. Once the material breaks the tool drops into the void, and if the operator does not release the trigger the breaker fires blank for a moment; that moment repeats with every break.
The symptom is in the sound. A seated breaker sounds dull and even; a blank firing breaker sounds ringing and metallic. We covered the distinction in its own guide, and the diagnosis side is on the blank firing page.
Too much pressure: invisible load on the boom
Pressing harder does not make a breaker break more. Its blow energy comes from the hydraulics, not from the boom. Pressing with the boom only guarantees that the tool stays in contact; anything beyond that adds nothing.
What it does add is load. Pressed hard enough to lift the front of the machine, the boom, arm and pins work under a static load, and that load arrives with vibration on every blow. This is why cracks show up over time in the boom’s weld seams.
The practical measure is this: while the breaker works, the machine’s tracks or tyres should not come off the ground. If they do, there is too much pressure.
Angle: why perpendicular?
Blow energy travels along the tool axis. With the tool square to the face, all of that energy goes into the material. At an angle, a component of it becomes lateral force, and the only place that force can go is the bushing.
The mark lateral force leaves is familiar: one-sided polish on the shank, oval wear in the bushing, and the tool gradually wandering off axis. These look like a material quality problem and are usually an angle problem.
In practice perfectly square is not always possible; on a sloping face or in a tight spot the tool cannot always sit square. The rule then is: correct the angle by repositioning the machine, not by twisting the breaker.
If the tool slips, release the trigger
If the tool starts slipping across the face while working, do not try to reposition it with the breaker still firing. A slipping tool takes its greatest lateral load at exactly that moment. Release the trigger, reseat the tool, then start again. Those few seconds are the habit that extends bushing life more than any other on site.
Do and don’t
Do
- Set the tool square to the face; build the angle by positioning the machine.
- Press enough to carry the breaker’s own weight, not much more.
- Release the trigger the moment the material breaks; do not let it fire as the tool drops.
- If the tool starts slipping, stop and reseat it.
- Listen to the sound; a change in it is the earliest report that the pressure has gone wrong.
Don't
- Do not press hard enough to lift the front of the machine.
- Do not carry on at an angle on the grounds that "it still breaks".
- Do not walk a firing breaker across the face.
- Do not try to lever material apart instead of breaking it; that is a separate and heavier mistake.
- Do not pull the trigger before the tool is seated; every blank blow comes back into the internals.
Does the tool type change the angle?
It does not change the rule, it changes the tolerance. A moil point loads a narrow spot and is the most likely to slip if set at an angle. A blunt tool spreads over a wide face and carries small angular deviations better.
A chisel is direction sensitive: its edge has to be set against the direction of the crack, or the energy does not travel in the plane you want. Here angle covers not only squareness but the orientation of the edge.
What each tool type does in which material is covered on the tools page and in its own guide; the subject of this one is the pressure and angle discipline that applies whatever the tool.