What Type Of Files Do CNC Machines Use?

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  CNC Machines Use Files In Four Layers, Not One
• 2
  Design Source Files: What Your CAD Model Must Carry
• 3
  CAM Files: Where Toolpaths And Fixtures Get Defined
• 4
  Machine Code: The Only File The Control Executes
• 5
  Support Files That Keep A Job Traceable
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  How A File Moves From Your Desk To The Spindle
• 7
  File Formats Compared By Machining Use

A CNC machine does not open your model. It runs a text program of coordinates, feeds, and spindle speeds. Everything before that program is preparation. So the answer to which CNC machines use files is really four layers: the design source, the CAM project, the machine-executable code, and the supporting paperwork.

Each layer has a different owner. Your CAD file belongs to design. The CAM project belongs to the programmer. The G-code belongs to the machine control. The setup sheet and inspection report belong to the shop floor. Mix them up and the part stalls before the first cut.

The order matters because errors flow downhill. A missing thread callout in the solid model becomes a wrong toolpath in CAM, then a wrong hole in the finished part. No amount of careful machining fixes a bad file. Most scrap we see starts upstream, not at the spindle.

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  Design sourceThe solid model that defines geometry, tolerances, and material.
• 2
  CAM projectToolpaths, stock, workholding, and cutting parameters.
• 3
  Machine codeThe G-code and M-code the control actually executes.
• 4
  Support filesSetup sheets, tool lists, inspection reports, and certificates.

The design source is the first file in the chain and the one you control most directly. It defines the nominal geometry, dimensions, and tolerances of the part. Neutral formats such as STEP and IGES carry surfaces and solids without tying you to one CAD package. Native formats such as SOLIDWORKS .sldprt or CATIA .CATPart keep the feature tree and parameters intact.

Neutral wins on compatibility. Native wins on editability. If we need to adjust a boss height or change a fillet radius, a native file with a live feature tree saves a rebuild. If your CAD seat differs from ours, STEP avoids translation surprises.

STEP is the safer default for most jobs. It is widely supported, handles complex solids well, and keeps units consistent when exported correctly. IGES handles older surface models but can split a solid into loose faces. That fragmentation creates gaps a CAM programmer has to stitch before toolpathing.

For 2D work such as plate profiles and sheet metal flats, DXF and DWG are still common. They carry no Z depth, so they suit laser, waterjet, and routing more than 3-axis milling. Send a DXF for a flat bracket and you are fine. Send one for a contoured pocket and we cannot read the floor.

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  STEPBest all-round neutral solid format for machining.
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  IGESOlder surface data; expect repair on complex parts.
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  Native CADKeeps parameters so edits stay fast and clean.
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  DXF and DWG2D only; good for plate and sheet profiles.

Once the design is frozen, the model goes into CAM software. The CAM file is not a universal format. It is a project file tied to a specific package, such as Mastercam, Fusion 360, or NX. It holds the toolpaths, the stock definition, the workholding, and the cutting parameters.

This is where engineering judgment enters the file. A programmer picks tool diameter, stepover, feed rate, and spindle speed for the material. Aluminium 6061 cuts fast and cool. Titanium Ti-6Al-4V runs slow with heavy coolant. Same geometry, very different CAM settings.

The CAM project also decides how many setups the part needs. A three-axis job may need four sides machined in four orientations. A five-axis job can reach those faces in one or two setups, which cuts handling error. That choice is made in CAM, not at the machine.

You rarely send a CAM file to a shop. It is internal working data. What we need from you is the design source, the tolerances, and the critical features. From there our programmers build the CAM project and the post-processed code.

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  Package-specificMastercam, Fusion 360, NX files are not interchangeable.
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  Holds parametersFeeds, speeds, stepover, and tool selection live here.
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  Defines setupsThree-axis versus five-axis access is decided here.
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  Not sharedCAM stays with the shop; you send the model.

The machine-executable file is plain text. It contains G-codes for motion, M-codes for machine functions, and coordinates for every tool move. Common extensions are .nc, .tap, .gcode, and .txt. A post-processor converts the CAM toolpath into the dialect your specific control expects.

Dialects differ. Fanuc, Siemens, Heidenhain, and Haas controls share the core of ISO code but differ in canned cycles, tool compensation, and high-speed look-ahead. A program written for one control may need edits before another runs it. This is why post-processors are matched to machine models, not just brands.

On our floor, 16 simultaneous 5-axis machining centers run posted programs tuned to each machine. The same part can be posted for a 3-axis mill and a 5-axis center, and the two programs look different. Both cut the same geometry if the post is correct.

You normally do not generate G-code yourself. If you already have verified code and a matching machine, we can review it. Otherwise our programmers post it from the CAM project. Sending hand-written G-code for a complex part usually costs more to verify than to regenerate.

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  Plain textG-code is readable ASCII, not a binary format.
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  Control-specificFanuc, Siemens, Heidenhain dialects differ in detail.
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  Posted, not typedA post-processor generates it from CAM data.
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  VerifiableWe simulate before the first cut on the machine.

The fourth layer is paperwork, and it is the layer buyers forget. A setup sheet lists the operations, the fixture, the datum, and the tool numbers. A tool list records the cutters, their offsets, and their remaining life. Without these, a proven program is hard to repeat on a second run.

Inspection files matter just as much. For a medical or aerospace part, a first-article inspection report ties measured values back to the drawing. We run 100% inspection before shipment and keep reports on request. That data is a file too, and it travels with the part.

Certificates close the loop. Material certs prove the alloy grade. ISO 9001:2015 and IATF 16949:2016 system records show the process was controlled. For regulated industries, ISO 13485:2016 and ISO 27001:2022 cover device quality and information security.

If your project needs an NDA, we sign one before files change hands. Uploads are secure and confidential. That protects the design source as much as the finished part.

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  Setup sheetOperations, datums, fixtures, and tool numbers.
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  Inspection reportMeasured values linked to drawing callouts.
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  Material certsProof of alloy grade and heat lot.
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  NDAAvailable before any file transfer.