From 3D model to finished workpiece: CAD/CAM in the CNC workshop
How to become really skilled in your trade
The use of CAD/CAM systems to develop CNC programs is what distinguishes the CNC technician (level 2) from the CNC assistant (level 1). While G-code was once written by hand, today the part is drawn and programmed on screen and the software generates the code. But software is only as good as the operator — wrong strategies or unrealistic cutting data cause havoc, no matter how good it looks on screen.
§CAD and CAM are two parts of the same chain
CAD (Computer Aided Design) is the drawing itself — the 3D model of the part with all dimensions and tolerances. CAM (Computer Aided Manufacturing) is the layer on top where you determine how the part should be made: which surfaces should be machined, in what order, with which tools and with what cutting data. Many systems (such as Fusion 360, Mastercam, SolidCAM, NX) include both but the tasks are different: CAD is about geometry, CAM is about process.
§Tool paths and strategies
In CAM you choose machining strategies which the software converts to tool paths. A roughing strategy clears rough material quickly; a finishing strategy runs the final contour with fine steps for a nice surface. You set cutting depth step over engagement and cutting speed for each tool. Modern strategies like adaptive/trochoidal milling keep constant load on the blade and spare both tool and machine by avoiding full engagement at corners.
- 01Scrubbing — remove as much material as possible in the shortest time
- 02Residual material processing — take what the grinding tool couldn't reach
- 03Deletion — the final contour with tolerance and surface requirements
- 04Boring and threading — holes and threads with the right cycles
§The postprocessor: the critical translator
The CAM system internally works with a neutral description of the tool paths. For the machine to understand them they must go through a post-processor — a translation program tailored to your specific machine's control. The post-processor writes the G-code in the dialect your Fanuc Siemens or Heidenhain expects with the correct codes for tool changes cooling and zero points. An incorrect or unadjusted post-processor is a classic source of error: the path is right in CAM but the code becomes wrong on the machine.
§Simulation before chip
Before the program is put on the machine, you run a simulation. CAM software can show material removal step by step and warn about collisions between tool, holder, piece, and clamping. A full machine simulation even accounts for the machine's own movement limits. It's far cheaper to discover a collision on screen than to break a tool or hit the chuck. Finally you often run a trial run in air or in soft material before the actual piece is clamped.
| Led | What's happening | Typical source of error |
|---|---|---|
| CAD | The part is drawn in 3D | Incorrect measurements or missing tolerances |
| CAM | Strategies and cutting data are selected | Unrealistic cutting data. |
| Postprocessor | Translation to G-code | Incorrect dialect for the machine |
| Simulation | Track inspection | Skipped due to time pressure |
§Documentation closes the chain
A CAM project is not finished with the code. There is an assembly documentation that goes with it: which tools sit in which positions how is the item clamped where is the zero point and what cutting data apply. This documentation means the next operator can set up the job again half a year later without guessing. Good documentation is not bureaucracy — it is what turns a programme into a reusable production resource rather than a one-time solution.
“CAM draws the paths, the post-processor translates them and simulation saves you — but it's the technician who bears the responsibility all the way.”