Router plunging through wood

lately I’ve had a couple of instances of my router plunging through the wood and ruining a project (usually on keyhole cuts). I follow the same process of zeroing out my z axis (I use a fence so X and Y are the same all the time) and I have trippled checked my max depth and depth per pass…fortunately it has been on pine, so not too costly other than my time. Has anyone else had this issue? Here is my basic process:

  1. initialize machine (pro settings)
  2. open my file and set parameters for wood depth
  3. save the gcode on the file
  4. set my z axis (it seems sometimes my Z axis is not holding?)
  5. load the job
  6. run the job

Any thoughts?


If that doesn’t help, let us know at and we’ll do our best to assist.

this happens intermittently…sometimes it cuts just fine and other times it plunges…no idea what the issue is. I read through the articles and made a couple of adjustments…it hasn’t happened again, yet. Anyone else have insight?

I once changed a bit after initialization, set zero with with a sheet of paper and the new bit. When the job started it ran the bit setter, which effectively threw out my zero, and jammed the router collet into my work piece. Fortunately it was only pine, and just a bit holder, so it didn’t matter too much. Doesn’t really sound like what’s going on in your case, but thought I’d toss it out there.

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Wish I wasn’t writing this but twice recently I experienced the same. Normal BitZeroing routine then a deep plunge at the start of a toolpath. After a quick pause/stop and re-zeroing I’d run the same toolpath successfully.

Such experiences really insert doubt into milling-confidence.

I’ll keep monitoring for others’ similar experiences.

This doesn’t really address the root cause, but, in my opinion, are good practices:

  • When naming files, include where the zero height is (i.e. Smith Welcome Sign Z_Bottom XY_Center). This creates the habit of checking where you should set zero. If you change this often, it’s easy to get confused and might lead to zeroing that could ruin a work piece.

  • Observe/note the actual Z position when zeroing and using the BitSetter. If the values make a large change relative to your tool offset or the Z value simply doesn’t appear correct (i.e. Z = 31mm but the end mill is only 10mm from where Z-zero should be), that may be a sign that you are heading for an air cut (Z too high), or worse, a plunge into your work piece (Z too low).

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When you say “after initialization”, do you mean:

  • as part of the initialization process where CM will prompt you to insert a bit and then automatically go to the BitSetter
  • or after this first probing was done with a given bit, you later swapped it with another one and re-zeroed? In this case, doing so without using the “Change Tool” button would throw out the tool length measurement indeed.

Only ever change the bit either when prompted by CM or after using the Change Tool button, and no other cases, also make sure your Z zero reference is consistent (top or bottom) between what’s in the design file and where you actually zeroed, and you should not have this kind of issues, ever.

Note: people here would probably say this is a mantra we keep repeating on the forum, but this is only because there was never any case where we could determine that depth was incorrect even though the setup was correct/consistent and the required workflow was followed.

If someone can come up with a repeatable way to reproduce the problem, while also documenting in lots of detail what the steps were, it would be quite interesting, to figure out if there is a residual bug in a corner case (spoiler alert: probably not)

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I changed the bit after the first probing was done, but before the job was started and I was prompted to change the bit. A stupid beginner mistake, better to make it on this project then later down the road on something that would have mattered more.


Julien, I am only changing bits when prompted and I use a bitsetter at every tool change (Pro). I always set my stock thickness for each job (using a micrometer) and always zero from the top of the stock. have a fence for X and Y but reset zero for each job by touching off the stock. It’s almost like after I zero/touch off, the zero doesn’t hold. I just don’t get what I’m doing wrong. Travis above referenced “milling-confidence.” Mine is not good at the moment! I have managed to salvage a few pieces of hardwood this has occurred with, and I have probably tossed 4 or 5 softwood pieces (only because they’re cheap). I’m not just hobbying…I’m selling products so this is costing me time and money! There is something small that is affecting this inconsistency and I just don’t know enough to find it myself.

Can you confirm what the “required work flow” should be?


If you do this and still have the issue, it will be interesting to dig into why it happens. If you artificially do an extra “Change Tool” on purpose (without actually changing the bit), does this make the problem go away ?

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Hey David,

Can you explain in more detail what is involved for you when you “set the stock thickness for each job” ?

Before I export the G code I open my project in Carbide Create and in the setup menu (gear icon) I make sure my stock sizes are correct (width, neight, thickness, zero height, etc.). I then “save” that setting (I do a variety of projects with the same basic layout so each time I go to produce one, I make sure the settings match the stock specs in job setup. After all of that I export the G code under a specific name/date, and then I load that project into motion. Is that helpful?

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It is helpful, David.

So far as I know, changing the height of the stock in CC doesn’t do anything at all to the toolpaths you generate. You’d need to go through all of the toolpaths and adjust the depths.

edit: see this feature request for details of the “stock bottom” implementation: Carbide Create - Changing thickness should update cuts that go to 'Stock Bottom'

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I have experienced the same thing four times today on four different projects. All of these have been created with Carbide Create Pro build 520 and are run via the latest Carbide Motion on a Shapeoko Pro XXL. In most cases, the machine will work just fine for a while and then suddenly take a deep Z-axis plunge.

Unfortunately, this was also my first time trying to mill purpleheart, so these errors cost me a bit more.

I have emails into support asking for their suggestions.