My friend Ron weighs about 300 pounds, and he's not fat. He needed to get a hole in a block wall about twenty feet (seven meters) up. So he got out his extension ladder
, an extension cord
and a rotohammer
. He hauled the drill up the ladder, took it in both hands and started drilling. Sometime during the drill the bit caught, and the chuck clutch
didn't release. The drill pulled Ron off the ladder, spun him one complete revolution until he ended up back on the ladder again. History does not record an underwear change.
Rotohammers are nothing more than a really big hammer drill. Sometimes called a 'macho drill' or 'hilti-drill' (after their first manufacturer) rotohammers have a pistol grip with guard where the drill is controlled. There is a second handle on the drill to help the user control the drill. Rotohammers produce a lot of torque. The drills often weigh more than 10 kilograms (without bit) and two macho drills cannot be used on the same 20 amp circuit.
Rotohammers may be used to drill holes up to a maximum 2 1/2" (7 cm) diameter in masonry. They are rugged, and the bits have a long life. Rotohammers don't care if the concrete is soft or fully cured, they work either way. But they're not very tolerant of thick iron rebar. The steel can catch inside the bit threads and twist.
Which is why all modern rotohammers have a clutch
designed to break torque when it exceeds what is needed to evacuate dust from the hole. These drills have broken a lot of arms, so they need to be used with respect and a working clutch. Most drills allow for the rotary drill motion to be turned off. With different bits rotohammers can be used as a jackhammer
to break up masonry, or to drive a ground rod
into the earth. Those bits do not have the spline gear, just the inset for the chuck pin.
Rotohammers use a distinctive chuck. Drill bits end in a spline gear with a concave section just ahead in the bit. The chuck is little more than a cylinder with a restraining pin that intrudes partly into the cylinder. The concave section in the bit is for the pin. Push on the pin and it slides aside so the bit can be inserted. Once released it springs back into place so the loosely held bit will not come out. When using one I like to pick up the (unpluged) drill by the bit to test the chuck engagement. If the drill comes with the bit, the chuck is properly engaged.
Rotohammers are popular because they are rugged, the bits have long life, and because they can be used to hammer and drill. They are not cheap, but cheaper than a wet core system, and the holes start more easily. On the negative side, they are heavy and you cannot drill through any metal larger than a light mesh. They are stronger than you are. They are stronger than your bones. So they must be used with great care by those who don't enjoy life in a cast. But they do work, and one will be found on almost every construction site.