Which is better is the better option, CNC Turning or CNC Milling?

When looking at turning vs milling consider both CNC turning and milling are categories of CNC Machining. I would like to clarify that your question is trying to distinguish between CNC turning (Like a lathe where the workpiece / part rotates) and CNC milling (Where the work piece remains fixed and the cutting tools rotate.)

It is difficult to generalize, because there is such a variety of CNC turning and milling machines (and turn -mill machines!) available. I cannot say- for example- that milling will out perform turning, just because I can gang mill several parts at once. Gang milling (by using the proper fixturing to hold multiple workpieces) allows the simultaneous machining of multiple parts on a CNC Mill. In contrast to a single CNC Turning machine, which works on a single workpiece at a time, this seems like a productivity advantage. However, there also exist a number of high quality, high capability, multi- spindle CNC turning machines which are running five, six, or 8 spindles simultaneously creating features on parts in each spindle with in the jobs “cycle time.”

Probably 60 percent of turned parts need to have some subsequent machining operation performed on them- slots or grooves or bolt holes. A CNC Turn-Mill machine with Y-axis could drop these parts complete. And we haven’t even started to consider Swiss sliding headstock machines…

Which is superior?

Rather than claiming that turning or milling are superior to the other, the best way to think about these complementary technologies is to evaluate the requirements to make the part in the most statistically capable and economic way.

• What is the lot size?
• What are the required features, tolerances, relationships to machine axes and other features?
• Can the part be made on a standard machine, or are the geometries such that additional axis are needed?
• What equipment is available to the shop owner already?
• What are the abilities of the crew?

How to determine the path forward

Lot size and tolerance issues should be the primary determinants of the machine tool selection. Low production volumes argue against an expensive, more full featured machine tool. High production volumes requiring low part cost demand low cycle times and can amortize longer set up times needed for the more complex machine tools. If features need to be generated beyond the X and Z axis capability of CNC Turning machines, then a CNC Turn- Mill with Y axis should be considered to drop the part off complete, rather than going to secondary equipment. Some parts with complex geometries and little turning can be successfully produced on CNC mills or CNC Turn-mills.

Can you look at horsepower, accuracy, available tools speeds and say one machine is “better?” for those parameters? Perhaps.  But the real test is which machine will most capably and efficiently produce a given part at the market’s price point. That consideration goes beyond horsepower, spindle speed and precision and other spec sheet data points, though there is no denying these are important considerations.  Look at the parts that you expect to make. They will tell you whether a CNC Turning, CNC Milling, or CNC Turn-Mill would be the optimum machine for your requirements.

By Miles Free

Other articles to read

https://www.pmpa.org/cribsheet-no-121-iso-turning-what-does-it-all-mean/

https://www.pmpa.org/cribsheet-98-thread-milling/