Roughing and Re-roughing

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. 

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.

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.