You can create threads in metal for screws primarily by using a process called tapping, either manually with a tap wrench or with a power drill using a tap drill.
Here's a breakdown of the process:
Understanding Tapping
Tapping involves using a hardened steel tool called a tap to cut threads into a pre-drilled hole. The tap removes material to create a helical groove that matches the thread pattern of a screw or bolt.
Methods for Tapping
There are two main methods for tapping:
- Manual Tapping (Using a Tap Wrench): This method is suitable for small-scale projects or when precise control is needed.
- Machine Tapping (Using a Tap Drill): This method is faster and more efficient for larger projects or production environments.
Steps for Manual Tapping
- Drill the Correct Size Hole: Use a tap drill chart (easily found online) to determine the correct drill size for the tap you're using. The hole needs to be slightly smaller than the tap's major diameter (the widest part of the threads).
- Deburr the Hole: Remove any sharp edges or burrs from the drilled hole. This ensures a clean start for the tap.
- Lubricate: Apply cutting oil or lubricant to the tap and the hole. This reduces friction and heat, making the tapping process smoother and preventing damage to the tap or workpiece.
- Start Tapping: Insert the tap into the hole and apply gentle, even pressure with the tap wrench. Ensure the tap is perpendicular to the surface.
- Turn and Back-Off: Turn the tap a few rotations forward, then back it off slightly to break the chip. This helps to prevent the tap from binding or breaking.
- Continue Tapping: Continue turning the tap, periodically backing it off to clear chips and re-apply lubricant.
- Check the Thread: Once the tap has reached the desired depth, remove it and inspect the threads. Clean any remaining debris.
Steps for Machine Tapping
- Drill the Correct Size Hole: As with manual tapping, use a tap drill chart to select the appropriate drill bit.
- Setup the Drill Press or Tapping Machine: Secure the workpiece and the tapping attachment (if using) in the machine.
- Lubricate: Apply cutting oil to the tap and the hole.
- Start the Machine: Engage the tapping function, ensuring the tap is aligned correctly with the hole. The machine will typically control the tap's rotation and feed rate.
- Monitor the Process: Watch the tapping operation carefully to ensure the tap is cutting smoothly and without binding.
- Reverse and Remove: Once the tap has reached the desired depth, reverse the machine to remove the tap.
- Check the Thread: Inspect the threads for quality and clean any debris.
Important Considerations
- Material: The type of metal you are tapping (e.g., aluminum, steel, stainless steel) will affect the tapping process and the type of lubricant you should use. Softer metals like aluminum are easier to tap than harder metals like stainless steel.
- Tap Quality: Use high-quality taps made from high-speed steel (HSS) for best results.
- Tap Types: There are different types of taps, such as taper taps, plug taps, and bottoming taps. Taper taps are used to start the thread, plug taps are used for general-purpose threading, and bottoming taps are used to create threads close to the bottom of a blind hole.
- Safety: Always wear safety glasses when tapping metal to protect your eyes from flying chips.
