Z Axis Changes During Cut

The following has happened with gcode from both Fusion 360 and Aspire.

While running gcode, the z zero is reset to a much lower setting without any user intervention. I’m talking a half an inch lower. I have cut deeply into my spoil board on a few occasions. Luckily I missed the t-track! I had assumed this was due to some user error (it may still be), but now I’m not so sure. Tonight, I was cutting the Marvel Aztec calendar. I loaded the gcode, zeroed the x y and z, and began cutting. In less than two minutes into the cut, the zero reset so low, the collet made contact with the board! The 1/8 v bit came out and was below the surface of the wood.

I was standing over the machine and was able to stop it immediately. I stopped the program without shutting off the controller so I was able to see where the z was now set. It was about a half an inch lower than where it was set using the probe.

Without turning off the controller, or reloading the gcode, I reset the zero at some point above the wood without the v bit installed. I then ran the same program again without turning on the router to see if the problem would repeat at the same place in the program. This time, the program ran normally for about 5 minutes before I stopped it. After the successful dry-run, I reloaded the collet and 1/8 v bit, reset z zero using the probe and began a new cut.

This time, the program ran smoothly for a little over an hour. With no warning, the same thing happened again. The bit plunged down through the board. The zero for the z axis is now a half inch lower than where it was set at the beginning of the run.

This was not a v carve, I was using a profile path to trace the art. My depth was set to 0.07". Of course the simulation looks normal. The same thing has happened a few other times. One other program, was cutting pockets with a 1/4 end mill. I have made many successful cuts as well, but at this point, I don’t trust the machine.

Does anyone out there have any ideas on what could be happening here?

I have checked all bolts and the router mount and all look good. Everything is solid.

are you sure the bit isn’t falling out of the collet?

yes. on the second failure tonight, the bit was still securely in place after I stopped the cut.

Can you post the gcode? I’m happy to look at the gcode and look for something out of place.


marvel 24in small v.gcode (1.9 MB)

Here is the gcode used. It did simulate properly. I hope you find something I did wrong!!

I just don’t understand how the zero can reset during a cut. I did see a z axis drift before when 3D printing. That was caused by a loose set screw on the z axis coupler. I cannot find anything loose on the OF.

Can electrical interference cause this? I have the power cable from the router running inside of the coil that holds the z axis stepper motor cable. That was to keep the router power cable up and off of the table.

I found the problem! The connector to the stepper motor is bad. At least one wire inside the connector is loose. If I move the z axis up and down and move the cable from the stepper motor, the z axis begins to skip and stutter. I have a video of this.

How can I get this fixed?

contact support and they’ll send a new one.

I have emailed support. Thanks for the quick response, even on Christmas Eve!!! You folks are awesome.

For reference for anyone interested, here is a picture of the loose crimped wires. This is the male side of the z axis connection.


Thank you for updating us - I am happy you were able to find the problem - as this will no doubt help others as well.
Happy holiday,

Dennis, I too had a wire issue. Mine was with one of the Y rails. It was not getting powered due to a broken wire so the cuts were very poor. Support diagnosed it quickly and sent out a new cable on a Sunday!. It’s unfortunate that the connectors are so fragile, but we have a great support team behind us.

I just started having an issue with the Z drifting during the cut. I set the Z with the touch plate and I just checked the Z with the paper method and mine has moved .08 but it’s enough that it messes up my project. How do I test or know that it’s the stepper motor or the wiring?

Edit: OneFinity support told me this:

“ Since you’re running an unsupported, aftermarket spindle, and your issue is directly connected to the z axis which is where the spindle is, our support will be limited.

There’s two options we can take:

  1. you switch back to the supported makita router configuration and we can provide you with more troubleshooting assistance.
  2. you continue using your spindle, but you will be 100% reliant on the spindle manufacturer or community for assistance.”

Hey Timothy,

here is some relevant information for this frequently asked question.

You did not provide information about machine, firmware version and accessories (model/brand) in use.

Welcome to the forum!

I work with a guy who is new to woodworking (not CNC machines). He bought a bit that had a very thin layer of shipping oil on it to prevent rusting. He didn’t remove it and contaminated the collet. What he didn’t realize that he needed to remove the collet and clean it too. The next few bits also slipped and they had to be cleaned as well. Just because it’s not loose when you look at it after cutting doesn’t mean it didn’t slip some. That where the depth marking on the Amana (and others) bits is useful. If it’s not lined up after cutting the bit moved.


It could be the collet. I’ve noticed that the bits will only go on half way and will meet resistance, like there’s a lip on the inside of the collet. I can go past it but with force. I’ll order a new one.

Thank you for that suggestion.


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