Metric Thread Turning on a Lathe
The process of creating a metric thread on a lathe has been around for a long time, and it is a relatively straightforward procedure for properly trained machinists. The process consists of the lathe spinning and holding a work piece with a cutting tool, or tool bit, cutting a helical groove into the part, known as the primary thread. This primary thread needs to be cut to create the actual thread.
To begin the process, it is important that the lathe is set to the correct speed. This depends on the type and size of the thread, as well as the material that the thread is being cut from. Once the speed is set, the next step is to set the thread lead, or the number of turns, the thread will make per inch of length. This can be determined by the pitch of the thread, which is the distance between thread peaks. Knowing the pitch is important, because it dictates how many threads will fit into one inch, and therefore how much the lead needs to be set to.
After the lead is set, a tool bit with a metric thread cutting profile needs to be chosen and installed on the milling machine. Once the tool bit is in place, the thread cutting process can start. This is accomplished by advancing the cutting tool along the length of the thread, taking a few cuts until the required depth of the thread is achieved. This process should be done at the same speed and cutting speed as the initial setup.
Throughout the process, it is important to keep the cutting tool and work piece cool. This can be done by applying cutting oil to the part, and also by blowing compressed air through the work piece. This will dissipate the heat from the cutting process, ensuring a good quality thread.
Once the thread cutting is done, it is important to deburr and clean the threads. This will ensure that the thread does not have burrs, sharp edges, or other debris stuck in the thread, which would affect the performance of the thread. A finishing tool with a rounded end can be used to deburr and clean the threads safely.
When all the cutting is finished, a thread gauge should be used to make sure the thread pitch is accurate and the thread is meeting the correct specifications set out in the machining operations sheet. If any discrepancies are found, it may be necessary to re-cut the thread in order to get the correct pitch and diameter. It is important to note that the thread gauge should only be used to measure external threads as using a thread gauge on an internal thread may damage the part or thread.
Metric thread turning on a lathe is a straightforward task for a trained machinist. It is important to remember that the machining operations sheet should be followed in order to ensure a good quality thread is produced. Setting up the lathe correctly, cutting slowly and keeping the tool and work piece cool, deburring and cleaning the threads after the cutting process, and using a thread gauge to check the thread have all been discussed in this article and should be used to ensure a successful metric thread turning project.
