Short answer
A breaker tool is the steel bar that carries the piston’s blow into the material; it is the breaker’s only consumable main part and half the output sits in it. It has three sections and each does a different job: the shank, the upper part the piston strikes and the bushings hold; the retainer groove, the recess the pin or lock sits in; and the working end, the part that enters the material. Wear advances differently in all three, and which part finished in what way describes directly how the breaker was used. This guide is about what a tool is; which type to use where is covered separately.
Three sections, three jobs
That the three sections do different jobs also explains why a tool is made in one piece with a specific heat treatment: a single hardness would not be right for all three, so the geometry and the heat treatment are designed together.
- Shank: the upper face the piston strikes and the cylindrical body the bushings hold. It takes the blow and passes it down. What you want to see here is even, symmetrical wear.
- Retainer groove: the recess the pin or lock sits in. Its job is to hold the tool inside the housing, not to carry the blow. Crushing seen in this groove means the retainer has begun to carry load, and that is a usage problem.
- Working end: the part that enters the material. It is also what defines the tool type: moil, chisel, blunt or pyramid.
Why steel choice and heat treatment matter
A tool has to carry two opposing properties at once. For the working end to resist wear it has to be hard; but very hard steel is brittle and cracks under impact.
So tools are heat treated to be harder at the surface and tougher at the core. On site that translates into one thing: a correct tool shortens by wearing, while a wrong or poorly treated one ends by breaking.
Which makes looking at the fracture surface of a finished tool a valuable diagnosis. A tool worn evenly describes correct use and correct choice; a broken one means either the wrong type or wrong use.
Welding or re-hardening a tool is not correct
Building up a worn tool by welding, or trying to harden it on site by heating and quenching, is a common attempt and nearly always does damage. The heat treatment around the weld zone is destroyed, that area becomes brittle, and the tool breaks exactly there. A tool is a consumable; it is replaced, not repaired. The single exception is controlled dressing of a mushroomed end.
How it wears
- Shortening at the working end: normal, expected wear. The tool is replaced once its length falls below a given limit; the limit varies by model and is in the manual.
- Mushrooming: the edges of the end crushing and spreading. It results from heat build-up and, caught early, can be stopped by dressing.
- A one-sided polished mark on the shank: it shows work under lateral load and that the bushings are not wearing evenly.
- Crushing in the retainer groove: it shows the pin or lock has begun carrying load, usually connected to levering or lifting.
- Breakage: either a tool type unsuited to the duty, lateral load, or accumulated blank firing.
Tool diameter and breaker match
Every breaker has a tool diameter, and that diameter is designed together with the bushing bore. The clearance between them is needed for both lubrication and alignment; too small and the tool binds, too large and it will not stay on axis.
So a tool of a different diameter is not used even where the dimensions look close. In the same way, the diameter is preserved when bushings are replaced.
Why tool diameter is such a narrow tolerance question is covered in its own guide.
Which type where?
There are four basic types and the choice follows how the material behaves. A moil point loads a narrow spot and penetrates. A chisel sets its edge against the direction of the crack. A blunt tool spreads over a wide face and breaks by crushing. A pyramid tool balances penetration against durability.
On top of those there are variants: hard rock tools for abrasive material, and dust-flushed tools that blow dust out of the contact area.
Which type wins in which material is covered in the tool selection guide and on the tools page; this guide was about the tool itself.