Basics of Autodesk CNC machining

The basics of Autodesk CNC machining start with a solid model that describes the finished part. In Fusion 360 or Inventor, that model carries the design intent: hole sizes, wall thickness, fillet radii, tolerances. Before any toolpath exists, the model has to be suitable for milling. That means no zero-radius internal corners, no walls so thin they will chatter, and no deep pockets that need a tool longer than the feature is wide. Fix those in CAD, not in CAM.

The CAM environment then asks for three things the model cannot provide. First, the stock: a billet, a casting, or a pre-cut plate. Second, the work coordinate system, usually the top corner of the stock. Third, the machine configuration, which decides whether you have three, four, or five axes of motion available. Set these wrong and every toolpath that follows inherits the error.

A common mistake is modelling to nominal dimensions and assuming the CAM side will hold them. It will not. If a bore is called out at Ø10.000 mm with no tolerance, the machinist has to guess. Give the CAM programmer a real tolerance band, a surface finish target such as Ra 0.8–1.6 μm, and a datum scheme. Those three inputs decide tool selection and stepover more than anything else in the setup.

Store the model with its CAM setup when you hand a job to a shop. A native Fusion 360 file or a STEP file with a PDF drawing is enough. The drawing still matters because it carries GD&T, thread callouts, and notes the 3D model cannot express.

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  Stock definitionBillet, plate, or casting sets the first toolpath and the number of setups.
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  Work coordinate systemPick a datum the machinist can touch off with a probe or edge finder.
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  Machine configurationThree, four, or five axes changes what the toolpath can reach.
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  Tolerances and finishReal bands and Ra targets drive tool choice and stepover.

Fusion 360 groups its milling strategies into roughing, finishing, and drilling. Adaptive clearing removes bulk material with constant tool engagement, which keeps radial load steady and tool life predictable. It suits pockets and open faces. It is a poor fit for thin floors, where the tool pressure can push material down and spring back.

Finishing strategies follow the geometry. Parallel passes work on shallow slopes. Contour and ramp passes work on steep walls. Scallop passes follow curvature and give a more even finish on organic shapes. Pencil passes clean out internal corners left by a larger tool. The rule is simple: match the strategy to the local slope, not to the whole part.

Simulation is not optional. Run the stock simulation and watch for three things: remaining material that the next tool cannot reach, rapid moves that pass through the part, and holder collisions. A toolpath can be geometrically correct and still crash because the holder shank is wider than the cutter. Set the holder in the tool library, not just the cutter.

Tool libraries decide how much of this work you repeat. Build a library that matches the cutters on your machine: diameter, flute count, corner radius, stickout, and recommended feeds and speeds per material. Once the library is right, a new job is mostly a matter of picking tools and adjusting stepdown. For aluminium 6061 and 7075, high flute counts and aggressive ramping work well. For 316L stainless or Ti-6Al-4V, lower surface speed and heavier feed per tooth keep the heat in the chip.

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  Adaptive clearingConstant engagement for roughing; avoid on thin floors.
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  Parallel and scallopShallow slopes and curved surfaces; even stepover matters more than speed.
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  Contour and rampSteep walls and prismatic sides; predictable load.
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  Pencil passesClean internal corners after a larger cutter has passed.

Post-processing turns the internal toolpath into G-code your controller understands. Fusion 360 ships posts for Fanuc, Haas, Siemens, Heidenhain, and many others. The generic post is a starting point, not a finished product. Check the output for the correct work offset (G54 to G59), the right coolant codes, safe Z heights, and whether the machine expects arcs in G2/G3 or as linear segments.

Never run a new post straight into a production part. Cut the first article in a soft material such as POM or aluminium, or air-cut with the spindle off and the tool offset well clear. Watch the tool change positions and the retract moves. A single wrong G-code line can scrap a part or crash a spindle.

The software stops where the physical setup begins. CAM does not know that a vise jaw is in the way, that a 4,000 mm gantry cannot reach a feature, or that a deep pocket will need a tool so long it deflects. Those calls belong to the machinist and the process engineer. Send a drawing with tolerances and datums and the shop can flag them before cutting metal.

At GreatLight we run 127 high-precision CNC machines, including 16 simultaneous 5-axis machining centers, 12 four-axis mills, 27 three-axis machines, and 16 mill-turn centers. Maximum processing size is 4,000 mm. We hold ±0.005 mm on qualifying features and inspect 100% of parts before shipment. CAM files from Fusion 360, Inventor, or any other Autodesk product drop into that workflow without translation.

If you are still at the design stage, send the model. We return a quotation and a free DFM analysis within 12 hours, and production can start within 24 hours. No minimum order quantity, from one prototype to 10,000+ part runs.

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  Check the postWork offsets, coolant codes, safe Z, and arc format.
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  Air-cut firstProve the program with the tool clear of the part.
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  Hand off real dataModel plus drawing with GD&T and datums.

A CAM file is a plan, not an order. The shop still has to choose stock, build fixtures, set tool offsets, and prove the program. The more of that you leave open, the more questions come back before cutting starts. A clean handoff includes the model, the drawing, the material grade, the finish spec, and any features that are functionally critical.

Material grade changes toolpaths more than most designers expect. Aluminium 6061, 2024, 5052, 5083, 6063, 6082, 7075, and ADC12 all cut differently. Stainless 303, 304, 316, 316L, 420, 430, 431, 440C, and 17-4PH (SUS630) work-harden, so light rubbing passes shorten tool life. Steel 1018, 1045, 4130, 4140, 4340, and A36 are more forgiving. Titanium TA1, TA2, TC4 (Ti-6Al-4V), Inconel, and magnesium AZ31B or AZ91D need their own feeds and speeds.

Finish also drives CAM decisions. Anodizing, plating, powder coating, black oxide, bead blasting, tumbling, brushing, and polishing all add or remove a thin layer. If a bore must stay at Ø10.000 mm after hardcoat anodizing, the pre-finish size needs to allow for the coating thickness. Laser marking and engraving need a minimum character height of 1.5 mm to stay legible.

Send the CAM file only if you want the shop to check your toolpaths. Otherwise a STEP file and a PDF drawing are enough. Either way, keep the uploads secure. We treat every file as confidential and can sign an NDA on request.

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  Model and drawingSTEP plus PDF with GD&T, threads, and notes.
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  Material gradeExact alloy, not just aluminium or stainless.
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  Finish specCoating type and any size-critical features.
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  ConfidentialityNDA available; uploads are secure.