What’s a Hammer Drill?

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A hammer drill is a tool used to cut a cylindrical opening in a piece of stock, usually metal, before tapping it, which is the process of cutting threads into the inside surface to accept a screw. The tap itself is a carbide cylinder with sharp threads, inserted into the hole created by the drill and rotated to cut threads into the inside surface of the cylinder, forming the female half of a mating pair, like a nut. The male half, a screw or bolt, is formed using specialized dies to cut threads on preformed metal cylinders with a special die, in a process called threading.

The use of screws, bolts, nuts, and similar devices to fasten different things together has been a staple of human industry since at least the Middle Ages, and perhaps even earlier. While modern threaded fasteners are almost always made from metal, the earliest threaded fasteners were made from wood. The size of these steadily increased as the loads they faced, on devices such as ships and windmills, grew larger and larger. The tools used to make the mating components – the taps and dies – were usually handcrafted from metal by skilled craftsmen who would use them.

In a modern machine shop, a hammer drill is a hardened drill bit used to drill holes in metal. The most important consideration in selecting a tap drill is that it is the correct size for the tap that will be used to cut the threads. It’s crucial to remove as much metal from the hole as possible so that there is no more metal left for the faucet to cut through, which can significantly increase the stress on the faucet. The hammer drill is sized by its length, as well as its diameter, because the hole it drills is countersunk; that is, it is slightly wider at the top than the rest of the hole. This flare accommodates the spigot, which is slightly tapered at the tip. This taper makes it easier to position the tap before starting the thread cutting process.

Many modern craftsmen take pride in their skill at tapping and threading their own fasteners for custom work. When fabricating from sheet metal, for example, it’s often necessary to drill holes for nuts and screws to secure the piece to other components. Once this is done, the faucets are matched with commercially available bolts and screws. Hand tapping can be a time consuming job, however, as the tap is often reversed to break up and remove the metal fragments created. If this is not done, the fragments can interfere with the tapping process. Therefore, all commercially available fasteners are machine made and most of those used in custom work are also machine made.

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