Roughing and Re-roughing

By wrightj

In NX CAM we refer to a specific set of machining instructions as an operation.  For example, finish-milling a planar face would be one operation.  To spotdrill, drill, and bore a hole requires three separate operations.  Other software packages refer to operations as jobs or tasks. It is important to distinguish between operations and cut patterns.  In a previous post, I talked about different types of cut patterns.  In NX CAM, those cut patterns are available in several different operations – I can use the Zig-Zag cut pattern in both roughing and finishing operations.

Today I will address roughing and re-roughing (aka re-machining) operations.  Michelangelo was once asked, “How do you carve an elephant?”  He answered, “Take a large stone and carve away everything that is not the elephant.”  That is the essence of rough machining – take away everything that is not the finished design. 

I don’t have an elephant to carve (sorry), but I do have a mold cavity, and some stock that the mold will be made from. 

Mold.JPGMold Stock.JPG

Here is how re-roughing works: the NC Programmer starts with a large diameter endmill to remove material.  That is followed by a smaller diameter endmill that can reach into places the larger tool could not. This process can be repeated as necessary until the part is ready for finish machining. I usually reduce diameters by about ½ for each new tool, so if the first endmill is 40mm in diameter, then the second is 20mm, and the third is 10mm.

The following video demonstrates a roughing operation followed by two re-roughing operations.  Pay particular attention to the three ribs at the bottom of the cavity.

(view in My Videos)

Here are the three ribs as in the design file.


Here is a closeup of the aforementioned ribs after the last re-machining operation.



NX CAM is aware of the in-process work – in other words, it knows where excess material has been left by the previous operation, and ONLY creates tool paths in those areas.  That eliminates wasteful “air-cutting” and decreases overall machining time.  Re-roughing allows the most efficient (largest possible) tool be used wherever possible.

Re-machining is a good strategy for efficient roughing.  In my next post, I will examine an alternative form of roughing deep cavities.

Thanks for reading.

About the Author


Jim Wright has a Master’s degree in Business Administration from the University of Central Missouri. He has over 30 years of experience in the manufacturing industry, and over 25 years of experience in the CAD/CAM field. He serves as Field Support for Siemens PLM CAM products. Prior to his current role, he held stints as CNC Programmer, CAD/CAM Department Manager, CAD/CAM instructor, and Project Coordinator for Siemens PLM CAM software development.


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This article first appeared on the Siemens Digital Industries Software blog at