A Brief Analysis of the Functions of the CNC Informatique System

A part program arrives as text. The interpreter reads it block by block and turns G-codes and M-codes into machine actions: which axes move, how fast, which tool is active, when coolant comes on. On a modern controller this happens in milliseconds, so the operator sees smooth motion instead of a list of commands.

Look-ahead is the part most people miss. The control scans 20 to 200 blocks ahead before it moves anything, then adjusts feed rates so the machine does not overshoot a corner or stall on a tight arc. Short look-ahead on a cheap control is why small radii come out faceted even when the program is clean.

The interpreter also catches syntax errors before the cycle starts. A missing G43 or a wrong tool number stops the run early, which is cheaper than scrapping a 6061 plate at the last operation.

If you send us a program with a post-processor you have never run before, tell us the controller family. Fanuc, Siemens and Heidenhain handle modal codes and canned cycles differently, and a file that runs on one may need edits on another.

Interpolation is where the control calculates the path between two points. Linear interpolation moves in a straight line. Circular interpolation fits an arc from a start point, an end point and a radius or center. Both are exact math, but the machine only approximates them in small steps, and the step size sets the surface you get.

On a 3-axis mill, a 50 mm arc cut at 3,000 mm/min can show scallops if the servo loop cannot keep up. The control compensates by slowing feed on tight arcs, which is why the same toolpath runs slower on a small radius than on a straight wall.

Five-axis interpolation is harder. The control must coordinate three linear axes and two rotary axes at once, and any lag on the rotary table shows up as a mark on the surface. Our 16 simultaneous 5-axis centers handle this with high block processing rates, which is what lets us hold ±0.005 mm on contoured surfaces.

When interpolation is done poorly, you see it as chatter marks, faceted radii, or a wall that is thin in the middle. When it is done well, the surface measures Ra 0.8–1.6 μm straight off the machine.

A cutter is never the size on the label. Tool radius compensation lets the programmer write the part profile and let the control offset the path by the actual cutter radius. If a 10 mm end mill measures 9.96 mm, the operator enters that number and the control shifts the path by 0.02 mm. Without it, every pocket would be undersized.

Tool length compensation does the same in Z. It matters most on deep pockets and multi-tool setups, where a 0.01 mm error in one tool carries into the next operation.

Thermal compensation is the quiet one. A spindle running at 12,000 rpm for two hours grows a few microns, and on a ±0.005 mm part that is real. Controllers with thermal models adjust the offset as the machine warms up. Machines without them need a warm-up cycle before the first finish pass.

Backlash compensation covers the small lost motion when an axis reverses direction. Ball screws wear, and the control adds a fixed offset on direction change. It is a static number, so it helps most on older machines with repeatable wear.

• 1
  Radius offsetCorrects cutter size; entered by the operator from a measured tool.
• 2
  Length offsetSets Z zero per tool; critical on deep pockets.
• 3
  Thermal offsetDrifts with spindle temperature; needs a warm-up on tight parts.
• 4
  Backlash offsetFixed value on axis reversal; most useful on worn ball screws.

The PLC handles everything that is not axis motion: tool changer, pallet swap, spindle orientation, door interlocks, chip conveyor. It runs in parallel with the motion control, and when it is slow, cycle time goes up even though the program is fine.

Tool changer logic is a common bottleneck. A 24-tool umbrella changer takes about 3 seconds per swap; a chain changer can take 8. On a job with 40 tools, that difference is 3 minutes per part. For a 10,000-part run, it decides the quote.

PLC logic also enforces safety. Door interlocks, spindle inhibit and overtravel limits are not optional, and they are checked on every machine we run. If a control has been modified to bypass an interlock, we will not put it on a job.

For unattended lights-out runs, the PLC matters more than the interpreter. Pallet systems, broken-tool detection and in-process probing all sit in the logic layer, and they are what allow a machine to keep cutting after the operator goes home.

Not every part needs every function. A flat bracket with drilled holes and a 0.1 mm tolerance runs fine on a 3-axis machine with basic compensation. Putting it on a 5-axis center adds cost without adding value.

A turbine blade, a surgical instrument or an engine block with blended surfaces is a different story. Those need simultaneous interpolation, thermal compensation and probing, and they are the parts where a weak control shows up as scrap.

We run 127 high-precision CNC machines, including 16 simultaneous 5-axis centers and 16 mill-turn centers, with a maximum processing size of 4,000 mm. That range covers most of what comes through our door, from one prototype to 10,000+ part runs.

If you are not sure which function is limiting your design, send the drawing. We return a DFM analysis with the quote within 12 hours, and the feedback usually points at one or two features rather than the whole part.