• Patrick

What is CNC Turning?

Turning is the process of rotating a part and applying cutting tools to it. As the part rotates layers of material are removed until the desired part dimensions are met. Turning is performed on a machine called a lathe. Lathes can turn faces, external diameters and internal diameters. They can also broach, drill, ream and bore.

The process:

An operator loads a workpiece into a work holder called a chuck. Chucks use at 3 or more jaws. The jaws attach to the chuck and are adjusted to securely hold the part. Part can be gripped from the outside or inside. On specialized parts soft jaws can be used; these are machinable jaws that can be made specific to the part. The part or workpiece is secured to the chuck either manually or by auto chuck. It’s convenient to use a foot pedal, stepping on it will close the chuck securing the part.

The motor known as a spindle rotates the workpiece and chuck at varying RPM. The RPM depends on the parts dimension, cutting technique and material. Larger diameter parts will have a faster surface speed. Smaller parts need to be turned at higher rpm to meet the same surface speeds. Once the part reaches the proper cutting speed turning tools are applied.

Turning tools apply a cutting edge to the surface. As the part rotates the cutting tool slices material layer by layer. As the diameter decreases the tool is adjusted inward keeping the same cut depth. It will also move on the z axis, from the front of the part to the back of the part near the chuck.

There are many types of turning tools far too many to go over here. Modern machines are equipped with turrets that have several tools on board and can quickly rotate and perform different types of operations.

The Prep:

CNC Machines largely automate the turning process. Watching them work always intrigues me. They slice through hard materials like steel almost effortlessly, but there’s a bit of prep work before the parts get to the machine.

The part starts as a 3D file in a computer aided drawing (CAD) program. It’s then moved into a Computer Aided Manufacturing (CAM) program where tool pathing is created. Tool pathing is the directions the machine has to follow in order to complete the part. Once the engineer dails in the paths and runs a simulator he exports the GCODE.

GCODE is a code made up of different coordinates or moves, usually a letter followed by a number which corresponds to the machine function followed by a few numbers for movement.

-It basically looks like a bunch of numbers and letters, maybe I’ll teach you some.

The GCODE is then uploaded to the lathe. Machine specific offsets are set as each machine may have slight variations. Tools are inserted into the machine turret in the corresponding tool number. We insert the required chuck, accessories and slot in the part. Now we let the machine do it’s thing while our hand hovers over the emergency stop button. Once the first part completes we check it’s measurements and adjust the GCODE accordingly. When we are satisfied we move into production.

Thanks for reading this, I hope I illustrated CNC turning well. Feel free to drop a message in the comments or chat box if you would like to learn more about us or the processes and services we offer.