Determining the correct drill bit size for tapping a 1/8" pipe is crucial for creating a clean, strong, and accurately sized thread. Using the wrong size can lead to stripped threads, a poor fit, or even damage to your workpiece. This guide will clarify the process and answer frequently asked questions.
The short answer is that you'll need a #16 drill bit. This corresponds to a diameter of approximately 0.0625 inches or 1.5875 millimeters.
However, selecting the right drill bit involves understanding more than just the nominal pipe size. Let's explore the nuances:
Why Not Just Use the 1/8" Drill Bit?
You might think that a 1/8" drill bit (0.125 inches) would work, but this is incorrect. A 1/8" pipe tap creates threads inside a hole; the hole itself needs to be slightly smaller to accommodate the tap's cutting teeth. Using a drill bit the same size as the tap would be far too tight, leading to binding and potentially breaking the tap.
What is the Role of the Drill Bit in Pipe Threading?
The drill bit's purpose is to create a pilot hole—a precisely sized hole that provides sufficient clearance for the pipe tap to cut the internal threads without excessive friction or binding. The tap’s cutting teeth then form the threads within this hole. The pilot hole must be the right size to avoid damage or poor thread formation.
What are the Other Considerations?
Choosing the right drill bit involves a few key factors beyond the pipe size itself:
1. Material:
The material you are tapping will influence your choice, though slightly. Harder materials may require a slightly smaller pilot hole to avoid excessive stress on the tap. Conversely, softer materials may allow for a slightly larger hole. It is generally recommended to start with the standard size and adjust only if necessary.
2. Tap Type:
While less critical for a 1/8" pipe tap, the type of tap (e.g., hand tap, machine tap) can subtly affect the ideal pilot hole size. Hand taps may benefit from a slightly smaller hole than machine taps.
3. Accuracy:
Ensure your drill bit is sharp and accurate. A dull or worn bit will create an uneven pilot hole, potentially affecting the quality of the threads.
Frequently Asked Questions (FAQs)
What is the difference between a pipe tap and a machine screw tap?
Pipe taps create tapered threads ( NPT - National Pipe Taper) designed for sealing applications. Machine screw taps create parallel threads (e.g., UNC - Unified National Coarse). They serve different purposes and require different drill bit sizes.
Can I use a slightly larger drill bit?
While a marginally larger hole might seem less risky, it is best to avoid this. An oversized hole will result in loose, poorly formed threads that won't hold properly.
What happens if I use a drill bit that's too small?
A drill bit that is too small will bind the tap, potentially breaking the tap or stripping the threads in your workpiece.
By understanding the specific requirements of pipe tapping, and using a #16 drill bit (0.0625"), you'll be well-prepared for a successful project. Always prioritize using high-quality tools and working carefully for the best results.
