A tap is an tool that creates thread inside a hole, and a tap can break if a person use a tap incorrectly. A tap often breaks because the hole that a person drill is too small for the tap. If a hole is too small, the tap will experience too much torque, and too much torque will cause the tap to snap inside a workpiece.
A broken tap is difficult to remove and a broken tap can ruin a workpiece. NPT threads are tapered thread, and NPT threads use a 1:16 taper to create a seal. NPT threads dont rely on a perfect fit like straight threads do, but instead, NPT threads wedge themself together as a person tightens the fitting.
How to Tap NPT Threads Safely
Because NPT threads wedge together, NPT threads create a mechanical seal. Many people use PTFE tape or thread compound with NPT threads because PTFE tape and thread compound fill the tiny gap between the threads. Because NPT threads require a tapered fit, a person must drill a pilot hole that are the correct size for the NPT threads.
A reference chart provides the specific drill size that a person needs for various NPT thread sizes. A reference chart include standard letter sizes and decimal sizes so that a person can select the correct drill bit. Most drill sizes are selected so that the threads achieves approximately 75 percent engagement.
Because 75 percent engagement is the goal, 75 percent engagement provides a balance between structural strength and the risk of the tap binding. If a tap binds, the tap is more likely to break. A person should use a taper tap to begin the tapping process, and a person should not use a bottoming tap as the first tool.
A taper tap helps to ease the tap into the material, but a bottoming tap is designed to reach the bottom of a hole and a bottoming tap is more difficultly to use at the start of the process. A person should turn the tap forward one full rotation and then a person should turn the tap back one quarter turn. Turning the tap back one quarter turn breaks the metal chip, and breaking the metal chips keeps the flutes of the tap clear.
If the flutes of the tap are not clear, heat will build up in the tap, and heat can cause the tap to break. A person must use the correct lubrication for the specific material that a person is tapping. If a person is tapping aluminum, a person should use a light solvent.
If a person is tapping stainless steel, a person should use a heavy duty tapping compound. Using a heavy-duty tapping compound prevents galling in stainless steel, and prevent galling is necessary to create clean threads. If a person use the wrong lubrication, the person may create poor threads or the person may break the tap.
