Learn How To Cut Threads On A Lathe

In the field of carpentry, one has to work with various types of machines. These machines either make the work easier, faster, or both. Among them, a lathe machine is an excellent example of a useful device. You can use it to give various cylindrical, spherical, or round surfaces to a wooden or metal workpiece. The workpiece rotates with a spindle or chuck, and in the meantime, you carve out its surface using different tools like a chisel.

Meanwhile, threads are like a series of grooves on a cylindrical surface. These ridges can be inward (female thread) or outward (male thread). Today we will talk about the method to put threads on your lathe machine.

Thread Terminology

There is some basic terminology about a thread that you should know before working on it. Knowing them may help you to understand different factors of a thread or even this article. So, let’s have a look-

Pitch- The linear distance between one point of a thread to the same point of the next thread. You can easily measure it by measuring the distance between the highest points of two consecutive threads.

Lead- It is the distance of how much a single thread moves from its start to end towards the cylinder axis.

Major diameter- Measurement of the longest diameter of the thread. It measures between two crests in a reverse direction.

Minor diameter- Measurement of the shortest diameter of the thread. It measures between two ridges in a reverse direction.

Depth- The distance from the lowest point of a ridge to the highest point of a crest within a single thread. The measurement is directly towards the 90-degree axis on the axis of the cylinder.

Threads per inch- Number of threads in one inch.

Helix angle- The angle created on the highest point of a thread.

Thread angle- The angle created on the lowest point of a thread.

Look at this diagram to have a clear idea of thread terminologies

The Process of Cutting the Threads of a Lathe

Preparation

Before cutting the threads on your lathe, you will need to prepare some stuff. They will ensure a better experience. Go through these steps properly-

At first, measure the size at which you will cut the threads. As mentioned above, you have to measure the pitch, lead, major and minor diameter, and finally, the depth.

• Get any tool for turning that is made of carbide.
• Get a thread gauge for measuring the pitch.

Cutting the Thread- Read the instructions below carefully from top to bottom. Once you think that you grasped everything, then go for the project.

• Firstly, attach a chuck to a spindle. This chuck will hold the workpiece firmly as it rotates.
• Adjust the quick-change gearbox properly. It will depend on the measurement of the pitch of the thread. The gearbox is for keeping a good balance of speed between the spindle and lead screw.
• The tool will be positioned a bit towards the right angle. Use the thread gauge to do this.
• Make use of the cross and compound feed by shifting the threading tool. So, it stays close to the workpiece.
• Set the feed points to zero.
• Connect the half nut of the carriage to the lead screw. As a result, when the lead screw rotates, the carriage will shift forwards to a certain distance on every turn of the thread.
• Connect a thread chasing dial to the carriage. Since the carriage is connected to the lead screw, the worm gear will drive the dial. Performing this process will ensure that the split nut grips the piece after a certain amount of time before it gets a new thread.
• The thread chasing dial will have the same number of full and split parts.
• This dial will rotate as the lead screw rotates. But it is only when the split nut is not connected to the piece.
• You should set the dial properly based on the number of threads you are going to put. If it is an odd number, then the dial will have a numbered line meeting the zero on the reading. Any line should meet the zero on the dial as the split nut gets connected to the piece for even numbers.
• Put a cut on the piece without any cutting oil. When the half nut is at the end of the threads, disconnect it. Turn the lathe off. Use the cross-feed to disengage the tool. Also, take the carriage back to its starting position.
• See if the pitch is accurate. Use the screw pitch gauge to do the measurement.

• Using lubricating, adjust the compound feed between 0.2 to 0.5 mm. When you are near the end bypass, decrease that within 0.025 to 0.075 mm.
• Continue this until the depth is okay.
• Remember that the end pass will have a depth of 0.025 to 0.75 mm.
• After you are done, check if the size is okay with a thread micrometer.
• Chamfer the end of the piece.

Final Note

Remember that normally most threads are left-handed. So, we shifted the tool to the right. But if you want to make the threads right-handed, you will need to shift them towards the left. Setting everything right will make the result accurate.