How do you tap a blind hole?

As a mechanical engineering expert with extensive experience in manufacturing and machining, I can provide you with a detailed guide on how to tap a blind hole effectively. Tapping is the process of cutting internal threads in a pre-drilled hole. When dealing with a blind hole, which is a hole that does not go all the way through a material, the process requires a bit more attention to ensure a clean and accurate thread is achieved. Step 1: Choose the Right Tap The first step is to select the appropriate tap for the job. There are three main types of taps: taper, plug, and bottoming taps. For a blind hole, you will typically start with either a taper or a plug tap. - Taper Tap: This type of tap has a conical shape that starts with a smaller diameter at the front and gradually increases in diameter towards the shank. It's used to start the threading process and can be used for both through and blind holes. - Plug Tap: Similar to a taper tap, but it's designed to form threads that are closer to the bottom of the hole. It's ideal for blind holes because it can create threads closer to the end of the hole without the risk of the tap breaking through the far side. Step 2: Prepare the Workpiece Before you begin tapping, ensure that the workpiece is secure and properly supported. Use a vise or a clamp to hold the material in place. This prevents movement that could lead to inaccurate threads or damage to the tap. Step 3: Start with a Pilot Hole A pilot hole is a prerequisite for tapping. The hole should be slightly smaller than the minor diameter of the thread you intend to create. The depth of the pilot hole should be at least as deep as the final threaded depth. Step 4: Apply Cutting Fluid Using a cutting fluid can significantly reduce friction and heat, prolonging the life of the tap and improving the quality of the threads. It also helps to flush away chips from the hole. Step 5: Start Tapping Begin tapping with a slow speed and light pressure. It's better to start with a slower feed rate and then increase it as the tap begins to cut. This helps to ensure that the tap is properly seated and reduces the risk of breaking. Step 6: Use a Tap Handle or T-Handle Using a tap handle or a T-handle can provide better control and torque when tapping. It also helps to prevent the tap from being over-tightened or cross-threaded. **Step 7: Backing Out and Clearing the Chips** After each revolution, partially back out the tap to clear the chips from the hole. This prevents the buildup of chips that can damage the tap or the threads. **Step 8: Switch to a Plug or Bottoming Tap** Once you've reached the desired depth with the taper or plug tap, switch to a bottoming tap to finish the threading process. A bottoming tap is designed to form threads all the way to the bottom of the hole. Step 9: Clean the Hole After tapping, it's important to clean out the hole to remove any remaining chips or debris. This can be done with a tap wrench or by using compressed air. Step 10: Inspect the Threads Finally, inspect the threads to ensure they are clean, uniform, and meet the required specifications. A thread gauge or a thread micrometer can be used for this purpose. By following these steps, you can successfully tap a blind hole with precision and achieve high-quality internal threads.

You should tap through holes with a plug or taper tap. If tapping a blind hole, start with a taper or plug tap, clean out the hole after going as far as you can then finish with a bottoming tap. Either taper or plug taps can be had in the "Spiral pointed" version.Jun 10, 2016