How do you cut a thread?

The question "How do you cut a thread?" is ambiguous. It could refer to:

1. How do you cut an existing thread (like severing sewing thread)?
2. How do you cut a new thread (like creating threads in a hole for a screw)?

We will address both interpretations below.

Cutting an Existing Thread (Severing)

This is straightforward. You cut an existing thread (like sewing thread) using a sharp object, typically:

• Scissors
• Thread snips
• A knife
• A razor blade

Simply place the thread against the blade and apply enough pressure to sever it.

Cutting a New Thread (Creating Internal Threads)

This refers to threading, which involves creating a helical groove inside a hole to accommodate a screw or bolt. The references provide the basic steps for cutting an internal thread using a hand tap. This process is typically performed in metal or plastic.

Here's how you cut an internal thread using hand taps:

1. Drill a Core Hole (Pilot Hole)
   • Use a twist drill bit to create the initial hole. The size of this hole is crucial; it must be the correct diameter for the thread you intend to cut. This core hole provides the space for the threads to be formed.
   • (Reference: 1. Drill core hole (twist drill) First you need to drill a core hole with the twist drill. ...)
2. Countersink the Core Hole
   • Use a 90° countersink to create a chamfer (beveled edge) at the opening of the hole. This chamfer helps guide the tap straight and prevents damage to the starting threads.
   • (Reference: 2. Countersink core hole (countersink) Then use the 90° countersink to countersink into the core hole and make a chamfer. ...)
3. Cut the Internal Thread
   • Use a hand tap to cut the threads inside the hole. Typically, a set of three taps is used: a taper tap (for starting), a plug tap (for intermediate cutting), and a bottoming tap (for finishing threads to the bottom of the hole).
   • Apply cutting oil to lubricate the tap and reduce friction.
   • Turn the tap clockwise a few turns, then back it off slightly to break the chip and prevent binding. Repeat this process until the desired thread depth is achieved.
   • (Reference: 3. Cut internal thread (hand tap))

Example:

Imagine you need to create threads in a piece of aluminum to accept a 1/4"-20 bolt (1/4 inch diameter, 20 threads per inch).

1. You would first consult a tap drill chart to determine the correct core hole size. For a 1/4"-20 thread, the chart might specify a #7 drill bit.
2. Drill the hole with the #7 drill bit.
3. Countersink the top of the hole.
4. Use the taper tap, plug tap, and then the bottoming tap, in that order, to cut the threads.