A capstan lathe is a milling machine used to create the same parts over and over again. The cutting bits are mounted on a rotatable turret known as a capstan, which allows the user to quickly change the orientation of the bits for cutting without having to take off the first bit and then mount the second. A piece of raw material, sometimes known as a blank, is mounted into the capstan lathe and is then spun at high speed. The cutting tools, sometimes known as knives, are then used to cut into the blank to create a new shape or design.
When a new shape or design needs to be cut on the same blank, the tool turret can be rotated and a different knife can make contact with the rotating blank. This makes the capstan lathe quick and easy to use, which is important when the user is creating the same part over and over again from various blanks. All of the tools are already mounted on the capstan lathe, and with a simple turn of the turret, the user can make the necessary cuts. Older machines do require that the user rotate the turret manually.
Newer machines may use computer numeric controls (CNC). A computer can be programmed to rotate the blank at a specific speed, adjust tool depth and contact, and rotate the capstan or turret when necessary to create the proper cuts. The advantages of a CNC capstan lathe over a manual lathe include time savings, efficiency, and tight tolerances of cuts. The computer ensures all blanks are cut to within a certain tolerance, making a uniformity among the parts that most consumers or clients will demand. A CNC capstan lathe operator will have to monitor the machine once it is programmed, and he or she will need to add or remove the blanks from the headstock, but otherwise, the machine will perform much of the cutting without any human interaction.
Manual capstan lathe machines can also index the tools to a specific position to create parts repeatedly, but mechanical blocks will need to be placed by hand before the operation begins. The user will place bars or blocks strategically for each successive tool that will perform the cutting, and those blocks will have to be removed and then replaced if a different part is to be made. This adds a bit of time over a CNC machine, but saves time over other styles of lathes that do not feature capstans.