Tapping

A set of pipe taps

Tapping is the process of cutting threads on the inside diameter of a hole with a tool called a tap. It is used to thread holes for mounting:

• Pressure gauges
• Fuel meters
• Electrodes (Bolts)
• Safety valves
• Other

Types of threads

There are a few diffent thread systems that are used in spudgun construction

• NPT (National Pipe Taper)
• BSP (British Standard Pipe)
• NF (National Fine)
• NC (National Course)

The process

1. Mark and drill an appropriatly sized hole
   • The hole should be in an area where fittings or pipe overlap (double thickness)
     

     An appropriate cutting fluid for tapping holes. It is usually available at tool stores.
   • Find correct hole size with a Tap/Drill Chart
2. Insert the tap into the tap wrench
   • If you don't have a tap wrench, a normal crescent wrench can be used
3. Cut the threads
   • Be careful to keep the tap straight or you will end up with crooked threads
   • When tapping plastic (or any other material) be sure to use an appropriate cutting fluid such as RapidTap® made by Relton.
   • Apply downward pressure while slowly turning the tap clockwise 180 degrees, then back out 90 degrees counterclockwise to clear the chips
   • For tapered threads, stop as soon as the entire length of the hole is threaded