DIY Knowledge

Impact mechanism


Mecanismo percutor

Mécanisme de frappe

The term impact mechanism or striking mechanism is used in reference to impact drills, chipping and rotary hammers, impact wrenches and tackers.

A ratchet-controlled impact mechanism is used in case of impact drills. One rotating and one immobile crown gear are pushed against each-other. The serration allows the rotating teeth to slip over the fixed teeth and to fall into the recess behind each tooth after climbing over the top. The energy of the fall is transferred as impact to the tip of the drill bit. Impact force depends on applied operator pressure.

A mass-impact mechanism is a ratchet-controlled impact mechanism whereby the applied pressure is replaced by the increased mass of the rotating crown gear and a pressure spring.

A pneumatic hammer mechanism is used in rotary and chipping hammers. It consists of a piston and a striker which move back and forth inside a cylinder.

There is an air cushion between the piston and the striker which 
- transmits the motion of the piston to the striker,
- absorbs and stores the rebound energy after the impactor has made contact with the workpiece, and during the next forward stroke of the piston it provides additional acceleration for the striker.

The impact force depends on applied operator pressure.

A spring-driven striking mechanism is used in electric hammers. A spring steel angle is set to vibrate by a cam and drives the striker forward. The rebound energy is again stored by the spring lever and released during the forward stroke as with the pneumatic striking mechanism.

An electromagnetic striking mechanism is used in tackers. The percussive mass is moved electro-magnetically. The impact force can be adjusted.

A rotary impact mechanism is used in impact wrenches. The percussive energy is produced in tangential, and not lateral fashion. This means that the striking mechanism does not more forward, but in a circular fashion. This however with the same effect as the spring-driven striking mechanism.