Hammer drill or drill/driver
A hammer drill is similar to a standard electric drill, with the exception that it has a hammer action for drilling masonry. A hammer drill/driver has an ordinary chuck (up to ½ inch capacity) which clamps round or hex shaft bits in its two or three jaws. The hammer action can be turned on or off depending on the job at hand. The hammering action is provided by cam plates which make the chuck pulse forward and backward as the drill spins. The pulsing (hammering) action is measured in Blows Per Minute (BPM) with 10,000 or more BPMs being common. Because of the relative masses of the chuck and bit and the remainder of the drill the energy transfer is inefficient and can sometimes make it difficult for larger bits to penetrate harder materials such as poured concrete. Most eclectic hammer drills are limited to standard masonry bits no larger than1/2 inch in diameter.
SDS drills (rotary hammer)
The SDS drill or rotary hammer is a drill with an enhanced hammer action that when compared to a conventional hammer drill or drill/driver is able to deliver hundreds of times the energy per hammer blow. The SDS bit system has tool-free bit changes with automatic bit locking. To go with this it also has a different chuck design and special SDS drill bits to eliminate the possibility of bit slip, and also to withstand the force of its hammer action. For drilling big, or deep holes in masonry, especially really hard materials like concrete, the SDS drill will out perform any hammer drill. BTW the SDS format was developed by Bosch.
SDS drills operate in 3 modes:
1. Drill only; (like an ordinary drill, but maximum speed tends to be slower -under 1500 RPM and torque higher)
2. Drill and hammer; the above mentioned enhanced hammer drill action. In spite of the extra performance, SDS drills also tend to be somewhat quieter than the conventional hammer drill.
3. Hammer only, no rotation
SDS downsides
1. SDS drill bits are more expensive than conventional masonry bits (although usually last much longer).
2. You cannot put ordinary bits in an SDS chuck unless you fit a adapter chuck first. These typically extend the length of the drill further, and also do not allow use of the hammer mode. (Some SDS drills come with a replacement chuck for ordinary bits to correct this problem)
3. Even pro light-weight SDS drills tend to be a few inches longer than a conventional hammer drill. This can make them more awkward to use in confined spaces.
A typical hammer drill will cost between $70 and $120, and a rotary hammer between $150 and $500 (depending on bit size). For DIY use or to drill holes less than 1/2 inch in size, the hammer drill is an acceptable option (even if it’s somewhat more difficult to operate).