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Year 3 · Advanced CAD/CAM · 2024

CNC machining strategies in Siemens NX

Two complete design-to-toolpath projects: an alloy wheel produced by turning and prismatic milling, and a hubcap machined from both faces with 3-axis milling, all verified in simulation before a single cut.

  • ContextENGR6002 Advanced CAD/CAM, Oxford Brookes University
  • RoleIndividual project
  • SoftwareSiemens NX (CAD, CAM and verification)
Siemens NX CAM3-axis millingTurningToolpath verificationDesign for manufacture
Siemens NX toolpaths over the hubcap model

Key numbers

12
milling operations across two setups on the hubcap
7
cutters chosen, from a ⌀12 mm roughing end mill to a ⌀3 mm ball nose
100×100×25
mm billet machined from both faces
39,764
facets on the thin-walled hubcap, under the 40,000 limit

Alloy wheel: turning and milling

I modelled a 17-inch wheel inspired by the Romac Venom, simplifying the spokes and hub so it could actually be machined, and documented it with full technical drawings.

  • Turning: centre drilling, then roughing with a CCMT insert, finishing with a VCGT insert and grooving, front face and back.
  • Milling: bolt holes, counterbores and the spoke design, with internal corners filleted to suit the cutter radius.
Alloy wheel technical drawing with section views
Alloy wheel technical drawing with section views

Hubcap: two-sided 3-axis milling

  • Back face: four cavity mills, a planar profile and two guide-curve passes, stepping from rough (0.2 mm stock) to semi-finish (0.1 mm) to finish.
  • Front face: 3D adaptive roughing over eight levels, a cavity mill into the detail, then two area-mill finishing passes.
  • Tooling: picked cutter sizes, feeds (680–800 mm/min) and speeds (1,200–2,800 rpm) for each operation, sizing down where a larger tool removed too much or couldn't reach.
  • Efficiency: trimmed cut ranges and switched engage moves to plunge where no material was in the way, cutting wasted air time.
3D adaptive roughing toolpaths on the front face
3D adaptive roughing toolpaths on the front face

Verified before cutting

Siemens NX's 3D dynamic verification showed both faces of the hubcap machined to the intended dimensions. I also redesigned the part as a thin-walled hubcap for injection moulding and rapid prototyping, keeping the mesh under the 40,000-facet limit.

Operation analysis: the colour map shows the finished part against the target geometry
Operation analysis: the colour map shows the finished part against the target geometry

Gallery

Turning simulation on the alloy wheel back face
Turning simulation on the alloy wheel back face
Milling the spoke design
Milling the spoke design
Thin-walled hubcap for injection moulding
Thin-walled hubcap for injection moulding

Looking back

What went well

Building complete machining strategies in Siemens NX, from roughing to finishing, and choosing the tools, feeds and speeds for every operation myself. The verification runs confirmed both faces were cut to dimension, and tidying the toolpaths noticeably reduced wasted machine time.

Even better if

I'd run the toolpaths on a real CNC machine to compare simulated and actual cycle times and surface finish. I'd also push into 4- and 5-axis strategies to reduce setups and avoid the stair-stepping that 3-axis milling leaves on curved surfaces.

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