When working with metal bars and rods, you often need to cut small threaded holes. The tools used for the job are the tap and die. A tap is a cutter used to create threads inside a hole. Taps are round bars of hardened steel, ground square on one end and threaded on the other (figure A). The ridges between the threaded channels have sharp cutting edges.
A tap is fitted into a pilot hole in the metal piece and turned with a special type of wrench. Here are the steps to take before and during the tapping process: Materials:
Drill press
Drill bit slightly smaller than the diameter of the tap
Metal work piece
Lubricating oil
Vise
Tap
Tap wrench
- Drill a hole in the metal slightly smaller than the diameter of the tap. Apply lubricating oil to the metal as you drill to keep the metal from overheating (figure B). Wear safety goggles and long sleeves when drilling for protection from flying chips of metal.
- Clamp the metal work piece in a vise (figure C).
- Attach the tap wrench to the top of the tap. Apply lubricating oil to the tap's threads.
- Insert the lubricated tap in the hole in the metal, placing it perpendicular to the metal (figure D).
- Turn the tap wrench clockwise to rotate the tap. For the first few turns, exert moderate downward pressure. Once the first threads have been cut, pressure is no longer needed. After each turn, back the tap out a bit, remove burrs from the edge of the hole, and add more lubricant to the tap to keep it from breaking off in the hole.
Die Cutting The process of cutting a thread on the outside of a round piece of metal is known as die cutting. This method may be used to rethread an old carriage bolt: Materials:
Carriage bolt
Vise
File
Die
Die stock
Lubricating oil
- Clamp the carriage bolt with a vise (figure E).
- Use a file to cut a 30-degree angle off the top of the bolt (figure F). This will help get the die started in cutting the threads.
- Place the die in the center of the die stock, and tighten it into place (figure G). Position the die over the bolt, holding the die stock perpendicular to the bolt.
- Applying downward pressure, turn the die stock clockwise one or two turns (figure H).
- Remove the die and die stock. Brush away the metal chips, and repeat the process as needed to carve the desired amount of threads. Do not apply downward pressure after the first few threads are formed.
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