What Size Drill Bit for a 1/8" Pipe Tap?
Finding the right drill bit size for tapping 1/8" pipe threads is crucial for a clean, accurate, and strong connection. Using the wrong size can lead to stripped threads, a loose fit, or even damage to your workpiece. This guide will clarify the process and answer common questions.
The short answer is: You'll need a #16 drill bit (0.067") for a 1/8" NPT (National Pipe Taper) tap.
However, it's important to understand why and what factors can influence this choice.
Understanding Pipe Taps and Drill Bit Selection
Pipe taps, unlike machine screw taps, create tapered threads. This taper ensures a tighter seal when the pipe is joined with a fitting. Choosing the correct drill bit size ensures the tap has enough space to cut the threads cleanly without binding or breaking.
The size of the drill bit isn't simply the same diameter as the pipe. The drill bit must create a pilot hole slightly smaller than the root diameter of the pipe thread. This leaves enough material for the tap to cut the thread profile. Using a chart or calculator designed for pipe tap sizes is recommended for accuracy.
Why Not Just Use the Same Size Drill Bit?
Using a drill bit the same size as the 1/8" pipe would be too small. The tap wouldn't have enough material to cut the threads properly. It would likely bind, creating inconsistent threads or even snapping the tap.
What About Different Types of Pipe Threads?
While NPT (National Pipe Taper) is the most common type in North America, there are other pipe thread standards. The drill bit size will vary depending on the type of thread. Always double-check the specifications of your pipe tap to ensure you're using the correct drill bit.
What if I Don't Have a #16 Drill Bit?
If you don't have a #16 drill bit readily available, it's best to acquire one. Using a significantly different size can cause the problems outlined above. Substituting with a drill bit close in size but not exact risks compromising the quality of the threaded hole.
Tips for Success:
- Use cutting oil or lubricant: This reduces friction and heat, preventing damage to the tap and improving thread quality.
- Use a tap guide: A tap guide will help ensure the tap starts straight, preventing misalignment and broken taps.
- Apply even pressure: Avoid excessive force, which can snap the tap. Let the tap do the work.
- Check your work: Once you’ve tapped the hole, verify the thread quality and fit with the fitting.
By following these guidelines and using the correct #16 drill bit, you'll ensure a successful and strong threaded connection with your 1/8" pipe tap. Remember to always consult a reliable reference chart or calculator for the most accurate drill bit size for different pipe tap sizes and thread types. Safety first! Always wear appropriate safety glasses when drilling and tapping.
