Screw cutting refers the machining operation involved with cutting an internal or external thread onto a cylindrical component. Screwcutting also refers to all the various types of threads from common vee threads, square threads, acme threads, buttress threads and multi-start threads.
Screw cutting is usually performed in a lathe using a single point tool. Different pitches are possible by changing the turning relationship between the lead screw and the head stock of the machine. The headstock rotates the work piece, while the lead screw feeds the cutting tool along at a set rate per revolution of the spindle. A wide variety of thread shapes and sizes can be produced on one machine, including custom threads if required.
Tapered threads are also possible to screw cut however, a tapered turning, or copy turning attachment is required. All screw cutting or thread cutting operations can be easily replicated on a CNC lathe for large volume runs.
A specialized area of screwcutting is in the application of cutting drill threads. Drill threads are the tapered threads used on each end of a drill rod used for drilling holes for oil and gas extraction or mineral exploration. These threads are usually of the acme thread form and oilfield rods usually have a ‘fast taper’. Mineral industry rods commonly have parallel, square threads or reverse buttress threads.Very precise control over the sizes and thread fits are required to ensure maximum thread life. For oil industry drill threads, machine shops are usually required to have API certification. Most drill pipe thread ing requires a machine shop who has either lathes fitted with a tapered turning attachment, or CNC lathes with a large spindle bore. Machine shops screwcutting drill pipe also require access to approved thread gauges and for the petroleum industry they must be API certified.