Hammer drill
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A Hammer drill, also known as a "rotary hammer" or "roto-hammer", (see also rotary hammer drill) is a rotary drill with a hammering action. The hammering action provides a short, rapid hammer thrust to pulverize relatively brittle material and provide quicker drilling with less effort. Lower power units are usually titled as "hammer drills". Higher power units, usually labeled "rotary hammers", tend to be larger and provide bigger impact forces. Modern units allow the hammer and rotation functions to be used separately or in combination, i.e., hammer mode, drill mode, or both. When used in the hammer mode, the tool provides a drilling function similar to a jackhammer.
A hammer drill is well suited for drilling holes in masonry or stone. It is also used to drill holes in concrete footings to pin concrete wall forms and to drill holes in concrete floors to pin wall framing.
A hammer drill can either be a drill (such as the one illustrated here), or it can be a replacement chuck that is installed on a power drill. When the drill is set to the "hammer drill" position it allows the chuck to move backward and forward over a short distance, allowing a spring to be compressed. When the spring is compressed, the chuck assembly is pushed as far back as it can go against a small eccentric flange. Any rotation of the chuck causes this flange to push back and reverse the direction of travel. The combined action of the spring, eccentric flange and rotation, push the chuck back away from the body of the drill at regular intervals. Under normal operation this sequence causes the whole assembly to "kick" with each turn, jack-hammering the drill bit into the material as it rotates. This helps to break up the masonry so that it can be removed by the drill bit's flutes.
[edit] Usage
What's the difference between a hammer drill and a rotary hammer?
A hammer drill has a specially designed clutch that allows it to not only spin the drill bit, but also to punch it in and out (along the axis of the bit). "Punch" is probably too strong a word since the actual distance the bit travels in and out and the force of its blow are both very small. Let's say "jab." But the jabbing is very rapid -- thousands of "BPM" (Blows per Minute) or "IPM" (Impacts per minute -- same thing). And it's these thousands of tiny jabs that do the trick with concrete, using the masonry drill bit's carbide wedge to pulverize it for the spiral flutes to whisk away. The first time you use a hammer drill, you will be amazed at how much faster it drills. Oh well, "right tool for the right job" and all that... Hammer drills almost always have a lever or switch that locks off the special "hammer clutch," turning the tool into a conventional drill for wood or metal work. So you get two tools in one -- consolation for the fact that hammer drills cost more than regular drills. But for installers who never know what they're going to run into next -- concrete block or wood studs -- it's a very good deal indeed.
Rotary hammers are similar in that they also pound the drill bit in and out while it's spinning. But the similarity ends there. They use a piston mechanism instead of a special clutch. And what they deliver isn't a "jab" any more -- it's a real punch. You can drill much bigger holes, much faster. Rotary hammers have such force, in fact, that the usual masonry bits are no longer adequate. Their smooth shanks would be pounded loose from the tool's chuck in a few seconds. They need special bits which can lock into the rotary hammer, and keep on spinning while smashing away. Naturally enough, "special shanks" means that manufacturers were given the opportunity to create unique systems whose tools required bits that only they would sell. Good for them -- "Beta" versus "VHS" for us (if you're old enough to remember that battle). Over the years a fair number of these proprietary systems evolved. Quite a few have gone the way of "Beta," but things seem to have settled down now, and three systems have emerged as the clear winners: SDS, SDS-MAX, and SPLINE SHANK.
Rotary hammer drills have an oil filled gearbox, which helps to achieve an impressive durability considering the environment they work in.
Apart from their main function of drilling concrete, the rotary action can be switched off and use is made of just the percussive force. Chisel and point accessories are used for small chipping jobs. Plumbers and electricians use them for chasing masonry walls.
The type of work they do means that they need to have a clutch, which cuts in when the drill bit jambs, stopping the violent wrenching motion that a drill without a clutch would cause, when stopped suddenly at full revs. Saving both the drill and the operator from damage.
There are two causes of the drill bit jamming. Hitting reinforcing steel and a worn bit. In both cases the drill is disengaged from the bit and the jammed bit is backed out of the hole with vise grips or plumber's type wrench.
The worn drill bit shown, will still drill a horizontal hole, although of a slightly less diameter than originally. When a drill like this is used to drill holes down into a concrete slab, the flutes are so worn that they can no longer lift the dust out of the hole, which packs up in the hole and jams the bit.
[edit] External Links
Rotary Hammer Drill A non commercial help site.
