The Starrett tap and die chart is a valuable resource for anyone working with threaded fasteners, whether you're a seasoned machinist or a DIY enthusiast tackling a home project. Understanding how to use this chart effectively can save you time, frustration, and potentially costly mistakes. This guide will delve into the intricacies of the Starrett tap and die chart, explaining its organization and offering practical tips for its application.
Understanding the Starrett Tap and Die Set
Before diving into the chart itself, it's crucial to understand what a tap and die set is and how it works. Essentially, taps and dies are precision tools used to create internal (taps) and external (dies) threads in metal and other materials. Starrett, a renowned manufacturer of precision tools, produces high-quality tap and die sets known for their accuracy and durability. Their accompanying charts simplify the selection process for appropriate tap and die sizes.
Deciphering the Starrett Tap and Die Chart: Key Elements
The Starrett tap and die chart is typically organized by thread type and size. While the specific layout might vary slightly depending on the version, the core elements remain consistent:
1. Thread Type:
The chart will clearly identify the thread type, such as:
- National Coarse (NC): A common thread type in the United States, characterized by a relatively coarse pitch (distance between thread peaks).
- National Fine (NF): Another prevalent US thread type, featuring a finer pitch than NC threads, offering greater strength and resistance to vibration.
- Unified Coarse (UNC): A standardized thread type used internationally, largely interchangeable with NC.
- Unified Fine (UNF): The international counterpart to NF, offering similar advantages in strength and vibration resistance.
- Metric (M): A metric thread system, identified by its diameter in millimeters and pitch in millimeters per thread.
2. Thread Size:
This refers to the nominal diameter of the thread, expressed in either inches (for UNC, UNF, NC, NF) or millimeters (for metric threads). The chart will list a range of available sizes.
3. Tap and Die Sizes:
The chart will correlate the thread size with the corresponding tap and die sizes required to create those threads. It's important to note that tap sizes are often slightly smaller than the nominal thread size to allow for accurate thread formation. The chart will clearly indicate the sizes needed for each stage of tapping (if a multiple-stage tap is required).
4. Additional Information:
Some Starrett tap and die charts include additional information, such as:
- Thread Pitch: The distance between adjacent threads.
- Threads per Inch (TPI): The number of threads per inch of length for inch-based thread systems.
- Tap Drill Size: The size of the drill bit needed to create the pilot hole before tapping. This is critical for proper thread formation and to avoid damaging the material.
Practical Tips for Using the Starrett Tap and Die Chart
- Identify the Thread Type: Determine the type of thread you need to create or match (e.g., UNC, UNF, Metric).
- Measure the Thread Diameter: Accurately measure the diameter of the existing thread (if working with an existing part) or determine the desired diameter.
- Locate the Correct Row: Find the row on the chart that corresponds to your identified thread type and diameter.
- Select the Appropriate Tap and Die: The chart will specify the correct tap and die sizes for your chosen thread type and diameter.
- Use Proper Technique: Proper tapping and dieing techniques are crucial for achieving accurate and clean threads. Refer to a comprehensive guide on machining techniques for best practices.
Conclusion: Mastering the Starrett Tap and Die Chart
The Starrett tap and die chart is an indispensable tool for anyone involved in working with threaded fasteners. By understanding the organization and key elements of the chart and following the steps outlined above, you can significantly improve the efficiency and accuracy of your work, whether you're a professional machinist or a DIY enthusiast. Remember to always prioritize safety and use appropriate safety equipment when working with sharp tools.
