Why Is My CNC Cutting Air, or Plunging Too Deep? Check Your Zero
When a hobby CNC cuts above the wood or digs into the spoilboard, the usual culprit is a mismatch between where your design says zero is and where you set it on the machine.
Your new CNC router starts the job and the bit spins happily an inch above the wood. Or it does the opposite and plunges straight through the stock into the spoilboard. Or the cut lands in the wrong corner of the board. It’s a regular question on hobby CNC forums, and experienced users answering it usually start with the same thing: zero.
Two zeros that have to agree
There are really two “zero” settings involved:
- In your design or CAM software (Carbide Create, Easel, Vectric, Fusion and so on), the job setup asks where zero is: usually a corner or the center of the stock for X and Y, and either the top of the stock or the bottom (the table) for Z. This doesn’t move the machine. It tells the software where you plan to set zero.
- On the machine (in Carbide Motion, gSender or your machine’s control software), you jog the bit to a spot and set zero there.
The point regulars on the Carbide 3D forum make again and again is that the toolpath file doesn’t tell the machine where zero is. You have to set the machine’s zero in the same place you chose in the design.
What the symptoms usually mean
- Cutting air: the design and the machine disagree about Z. One mismatch forum regulars often ask about is a design set up with Z zero at the bottom of the stock while the machine was zeroed on the top of the material, which leaves every cut about a board’s thickness too high.
- Plunging too deep: the reverse mismatch has the opposite effect, as can a stock thickness in the design that doesn’t match the real board.
- Cut lands in the wrong place: X and Y zero were set at a different corner (or the center) than the design expects.
These aren’t the only possible causes (a wrong or outdated toolpath file is another), but zero is the first thing to rule out.
A routine that prevents it
- Decide on one habit and stick to it, for example lower-left corner, top of stock, and set every design that way.
- Measure your stock and enter the real thickness in the job setup.
- On the machine, jog to that same corner and set X and Y zero, then set Z zero on the top of the material (a touch probe makes this easier and more repeatable).
- Carbide 3D’s own instructions add one more rule for its machines: only change the bit when Carbide Motion prompts you or when you use its Load Tool button.
On a new project, it’s worth watching the first plunge closely, ready to pause or stop, so a zero mistake costs you a few seconds rather than a board.