Watts or joules when choosing a rotary hammer?

Joules. Impact energy is what reaches the bit on each blow and sets the rate of progress in concrete; watts only describe the motor's input.

Will an SDS-plus bit fit an SDS-max machine?

No. The shanks are 10 mm and 18 mm and the holders do not match. Adapters are not advisable for heavy breaking.

How many joules do I need?

2-3 J covers services, anchors and socket boxes. Breaking concrete and opening walls calls for 8-20 J, and floor breaking for more than 20 J.

Can a percussion drill replace a rotary hammer?

In brick and aerated block, yes; in concrete, no. A percussion drill's hammer action comes from ridged plates rubbing and carries very little energy.

Should the bit shank be greased?

Yes — a thin film extends the life of both holder and bit. A thin coat is enough; too much collects dust.

Does pressing harder speed up drilling?

No. The energy comes from the piston; extra force only heats the machine and the bit.

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Rotary Hammers & Breakers

A rotary hammer strikes the back of the bit with a pneumatic piston and breaks concrete by impact energy — which is why it advances incomparably faster than a percussion drill. This page explains what impact energy in joules tells you, how SDS-plus and SDS-max differ, and how the duty classes divide. The catalogue holds over 70 models.

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Impact energy and duty class

The figure that decides these machines is not watts but impact energy in joules: the energy delivered to the bit with each blow. Between two machines of equal wattage, the one with more joules advances faster in concrete.

Class	Impact energy	Shank	Work
Light	1-3 J	SDS-plus	Anchor holes, services, socket boxes
Medium	3-8 J	SDS-plus / SDS-max	Pilot holes, tile removal
Heavy	8-20 J	SDS-max	Breaking concrete, opening walls
Demolition	Above 20 J	Hex / SDS-max	Floors and slabs

SDS-plus and SDS-max

SDS bits are not clamped: they lock into the holder and stay free by a few millimetres along their axis, so the piston delivers its blow straight to the bit. SDS-plus has a 10 mm shank covering 4-30 mm holes; SDS-max has an 18 mm shank for heavy machines. The two do not interchange.

Three-mode machines select drilling, hammer drilling and hammer-only. Hammer-only turns the tool into a small breaker.

SDS-plus: 10 mm shank, 4-30 mm holes, services and anchors.
SDS-max: 18 mm shank, heavy drilling and breaking.
Three modes: drill / hammer drill / hammer only.
Vibration damping reduces fatigue over long spells.

Use and maintenance

A thin film of grease on the bit shank noticeably reduces wear on both holder and bit. Pressing harder does not speed the job: the energy comes from the piston, and extra force only heats machine and bit.

Stop hammer drilling when you hit reinforcement — rebar blunts a hammer bit. Use a rebar-cutting bit or a core drill instead.

Frequently Asked Questions

Watts or joules when choosing a rotary hammer?
Joules. Impact energy is what reaches the bit on each blow and sets the rate of progress in concrete; watts only describe the motor's input.
Will an SDS-plus bit fit an SDS-max machine?
No. The shanks are 10 mm and 18 mm and the holders do not match. Adapters are not advisable for heavy breaking.
How many joules do I need?
2-3 J covers services, anchors and socket boxes. Breaking concrete and opening walls calls for 8-20 J, and floor breaking for more than 20 J.
Can a percussion drill replace a rotary hammer?
In brick and aerated block, yes; in concrete, no. A percussion drill's hammer action comes from ridged plates rubbing and carries very little energy.
Should the bit shank be greased?
Yes — a thin film extends the life of both holder and bit. A thin coat is enough; too much collects dust.
Does pressing harder speed up drilling?
No. The energy comes from the piston; extra force only heats the machine and the bit.