Tapped Hole or Threaded Hole is a question

Many of us are confused about the twins products in machining: tapped holes and threaded holes, for their similar look and functions. Therefore, this article will clarify definitions of tapping and threading, unpack the correct usage of them, and identify the similarities and differences of these mechanical and significant components.

Understanding Tapped and Threaded Holes

Tapped holes result from cutting threads into existing holes. A tool called a tap creates these threads by removing material. Threaded holes, on the other hand, form during the manufacturing process. They're integral parts of components, often made through casting or molding.

Tapped Holes

Tapped Holes are created using a tool called a tap, which cuts threads into a pre-drilled hole. This process removes material from the inner walls of the hole, forming threads that match the profile of a screw or bolt. Tapping is cost-effective, widely used, and works well with a variety of materials. However, since it cuts the material, it can slightly weaken the surrounding area.

Threaded Holes

Threaded Holes, on the other hand, is a more general term. It refers to any hole containing internal threads, regardless of the method used to create them. Threaded holes can be made by tapping, but they can also be created through other processes like thread rolling (which forms threads without cutting) or thread milling (which uses a rotating tool for precision). Some threaded holes are pre-threaded using inserts in softer materials.

Similarities and Differences

Common Ground

• Both provide secure fastening solutions

• Used in various industries: automotive, aerospace, electronics

• Require precision for optimal performance

Key Distinctions

1. Thread Type
   Tapping is exclusively for creating internal threads. For external threads, other threading processes like thread rolling or using dies must be employed. Threading, on the other hand, covers both internal and external thread creation, making it more versatile in manufacturing.

2. Thread Variety and Customization
   Tapping offers limited flexibility in terms of thread variety. Each tap is designed for a specific thread size and pitch, so producing multiple thread sizes requires different taps. This restricts tapping from handling custom thread forms. In contrast, threading methods like thread milling allow for the creation of custom threads, making them ideal for complex or non-standard thread designs.

3. Tool Breakage and Durability
   Taps are more prone to breaking than other threading tools, especially when dealing with hard or brittle materials. A broken tap can be difficult to remove, sometimes leading to scrapping the entire workpiece. Thread milling or rolling tools generally offer greater durability and are less likely to break under stress, making them more reliable for difficult materials or tight spaces.

4. Blind Hole Depth Limitations
   One of tapping's key limitations is its difficulty in threading deep blind holes. Most taps have a tapered lead that prevents them from threading all the way to the bottom of the hole. This limitation makes tapping unsuitable for applications requiring full thread depth, where thread milling may be necessary to achieve deeper threads.

5. Material Limitations
   Tapping struggles with certain materials. Hard materials like hardened steel quickly wear down taps, making them ineffective and increasing tool replacement costs. Tapping is also problematic for very ductile materials, which can become "gummy" and stick to the tap, causing frequent interruptions for tool cleaning or replacement. Threading methods such as thread rolling often handle these materials better, improving both tool life and thread quality.

Aspect	Tapping	Other Threading Methods (e.g., Milling, Rolling)
Thread Type	Internal threads only	Internal and external threads
Thread Variety	Limited to specific sizes and pitches	Supports custom and non-standard threads
Tool Durability	Higher risk of breakage, especially in hard materials	Lower breakage risk, better for hard or ductile materials
Blind Hole Depth	Limited depth due to taper	Can reach deeper into blind holes
Material Flexibility	Struggles with hard or ductile materials	Handles a wider range of materials efficiently

In a nutshell, tapping is best suited for simpler, smaller-scale internal thread creation but has notable limitations in flexibility, durability, and material compatibility. For more complex or demanding applications, thread milling or rolling often provide more robust and versatile solutions.

Clarifications and Suggestions

Clarifications :

1. CNC Tapping vs. Hand Tapping
   CNC taps provide superior precision and efficiency compared to hand taps. While hand taps are suitable for manual operations or small-scale tasks, CNC tapping should be preferred in high-precision machining. CNC tapping ensures consistent thread quality and reduces human error, making it a more reliable choice for most applications.

2. Choosing Taps for Blind Holes
   For blind holes, bottoming taps are highly recommended due to their ability to form threads almost to the bottom of the hole. However, starting the process with a taper tap improves initial thread engagement, followed by switching to a bottoming tap for complete threading. This two-step process enhances thread definition, ensuring better engagement, especially in blind holes where depth precision is critical.

3. Avoiding Spiral Point Taps in Blind Holes
   Spiral point taps are less ideal for blind hole applications, particularly in CNC machining, as they push chips downward. This can lead to chip accumulation in the hole, which may interfere with assembly. For cleaner results, spiral flute or interrupted thread taps should be used. These taps are designed to pull chips upward and away from the hole, minimizing issues during assembly.

4. Thread Forming Taps for Stronger Threads
   Thread forming taps offer increased thread strength because they don’t cut material; instead, they compress it, creating stronger, more durable threads. These taps are excellent for applications requiring long-lasting threads and minimal breakage risk. However, they require a larger tap drill diameter, so precise calculations are necessary. Using a resource like Machinery's Handbook can help determine the correct drill size for thread forming taps.

5. Clearance Holes Are Not Threaded
   It's essential to recognize that clearance holes, though similar in appearance to threaded holes, are not tapped. These holes are slightly larger to allow fasteners to pass through and engage with a nut on the opposite side. They are designed to hold the threaded portion of the fastener, but not to engage with the fastener head.

Tap Selection Advice

When deciding on the right tap, the type of hole and material are critical factors. For blind holes, consider starting with a taper tap followed by a bottoming tap to achieve full thread depth and engagement. For blind holes in CNC machining, opt for spiral flute taps to avoid chip build-up, ensuring smoother assembly. If thread strength is a priority, such as in load-bearing applications, thread forming taps are recommended due to their ability to enhance thread durability and longevity.

Utilizing CNC taps over hand taps is a best practice for high-precision and repetitive tasks, ensuring consistency and reducing error. For hole diameters and tap sizes, referencing Machinery’s Handbook ensures accuracy in calculations, especially when using non-standard tap types like thread forming taps.

#Conclusion

In summary, while all tapped holes are threaded holes, not all threaded holes are tapped. Tapped holes are specific to the tapping method, while threaded holes encompass a variety of threading techniques that offer different advantages in terms of strength, precision, and cost. Both of them are essential parts in mechanical industry.