Thread cutting is a machining operation done using a lathe machine. A relative motion between the lead screw and the headstock rotation will facilitate the cutting of threads on cylindrical specimens with different pitches. In a thread, lead (the linear travel provided for one complete rotation) is calculated by the following equation: Lead = Number of starts in the thread x Pitch of the thread. Pitch is the shortest distance between the two adjacent, similar points on the thread. As per the formula, it gives the impression that the number of starts increases the lead provided by the thread. In a multi-start thread, every start initiates a thread, which is placed one after the other in an orderly fashion. Let us assume that a single thread of pitch 8 mm is made on a cylindrical specimen. In this case, the lead of the thread is calculated as 1 x 8 = 8 mm. Since there is one thread, the number of starts will also be one. Now let us make another thread, the second thread, with a starting point exactly 180 degrees apart from the first thread. This will provide an adjacent similar point exactly at half the distance in comparison with the previous case. This will reduce the pitch to 4 mm from 8 mm as per the definition given for pitch. Now the lead can be calculated as 2x4 = 8 mm. This shows that the lead is the same for both single- and double-start threads, indicating that the number of starts will not proportionately increase the lead. Hence, in a multi-start thread, the lead will be equal to the pitch of one thread in it. So, for what reason do multi-start threads exist? The answer is to increase the load-carrying capacity of the thread for applications that demand lifting heavy loads. Other applications include increasing linear displacement, fastening, and power transmission. Though multi-start threading has many advantages, the machining requires extreme care and skill from the operator. This is due to the fact that the relative motion between the headstock spindle and the carriage movement needs to be controlled as many times as the number of starts in the thread. Hence, to ensure accurate thread cutting with multiple starts, the operator needs to be trained. This article is predominantly aimed at giving a clear idea about the meaning of the multi-start thread by comparing it with the single-start thread. Though multi-start thread cutting can be done in many ways, lathes are predominantly used. Nowadays, CNC Machines are incorporated with the necessary features to cut multi-start thread with ease. This way, overall effort in the manufacture of multi-start threads has come down drastically. Moreover, the accuracy and the necessary tolerance requirements are all easily met, making it an error-free application product. Since conventional lathes need a lot of settings, CNC Machines are preferred to cut multi-start thread to increase productivity. This way, the cumbersome task of the operator is very much reduced significantly with a higher production rate by utilizing highly versatile CNC Machines.
This post first appeared on How Do Astronauts Survive In Space | Space Science?, please read the originial post: here
