9/16 x 18 Tap Drill Size
A 9/16 x 18 tap is a thread cutting tool used to create a threaded hole in a material. The 9/16 refers to the diameter of the hole, while 18 refers to the threads per inch (TPI).
Tap Drill Size
To properly tap a hole, you need to first drill a pilot hole with a specific size drill bit. This is called the tap drill size, and it's calculated to leave enough material for the threads to engage.
Calculating Tap Drill Size
The exact tap drill size for a 9/16 x 18 tap will vary slightly depending on the material you're working with. However, you can use the following formula as a starting point:
Tap Drill Size = Tap Diameter - (2 * Thread Depth)
Thread Depth is the depth of the thread in the hole, which is typically equal to 0.65 x pitch.
Pitch is the distance between two adjacent threads, and for a 9/16 x 18 tap, it's calculated by:
Pitch = 1 / Threads per Inch = 1 / 18 = 0.0555 inches
Therefore, Thread Depth = 0.65 x 0.0555 = 0.036 inches
Using the formula:
Tap Drill Size = 9/16 - (2 * 0.036) = 0.5625 - 0.072 = 0.4905 inches
Converting to Drill Bit Size
0.4905 inches is roughly equivalent to a 5/16 inch drill bit.
Note: This is just a general guide. You may need to adjust the tap drill size based on your specific application and material. Consult a tap drill chart or a professional for more precise guidance.
Factors to Consider:
- Material: Different materials have varying hardness and machinability, affecting the required tap drill size.
- Tap Type: Different tap types (e.g., hand tap, machine tap) may require slightly different drill sizes.
- Desired Thread Engagement: The length of the threaded portion you require will influence the tap drill size.
It's essential to use the correct tap drill size to ensure:
- Proper thread formation: A well-sized pilot hole allows the tap to cut threads effectively without binding or breaking.
- Sufficient thread engagement: The tap drill size leaves enough material for the threads to engage securely.
- Reduced risk of damage: Using the correct drill size minimizes the risk of damaging the tap or the material.
