Error (6) serial port unknown.... over heated spindle motor response?

Figured I’d think out loud to the great community here. I was 3-1/2 hrs of machining into a 5-1/2 hr machining of 2 combined parts. First part was 45min then a 5 min break to put new stock in and zero. Everything was running great, then at 2hr:45min everything stopped and Carbide Motion said: Error(6): Serial Port Unknown. From the looks of things the end mill didn’t crash into anything nor did it look like any other kind of physical over load. So I touched the spindle motor to see just how hot it was, from experience It felt hot enough to take a thermal reading. It read (141 F) -> (60.5 C) and it had probably been sitting there 10-15 min (cooling) in total before the actual reading was taken. That’s (roughly (18 F) or (10.5C) over the recommend (ambient temp of the manufacturer). However that’s the ambient temp… but would it be safe to assume being 18F surface temp over ambient limits would trigger an overheating fail safe?

I could see that a spindle would shut down if it got too hot but why would you get a serial port (USB) error. It may be that your spindle is hot but maybe your file is too big and that is the reason for the lost communication with the Shapeoko controller. You will have to research if your spindle has a thermal sensor and at what temperature it would shut down. The two things may not be connected.

You did not say what spindle your have but most of the spindles are rated to continuously run and cool themselves. It is summer and depending on your ambient air temperature in your shop it still may not have anything to do with the spindle and more about the file size. CM has been known to choke on very large files. Something that will run for 2+ hours is probably a big file. So if your spindle still runs try making more smaller tool paths.


Heat could be an issue… just machine a heatsink with your nomad. I might have the fusion file and everything.

This error for me is caused by spindle overloading and triggering a reset. I don’t think its happened any other time although I do feel the Nomad is a little more sensitive to emi.


Definitely Not an expert here but I do know there is no thermal spindle sensor. If it was a shutdown caused by excessive current draw you would (probably) see that the lit ring on the on/off button of the Nomad button had gone out.

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Oh and as @Vince.Fab just mentioned - I have heat sinks on my spindle motor as well. Ditto on the overload = similar error.


While your motor may be hot, I doubt the problem is caused by this. I would say that you probably had one of the following: static discharge e.g: ungrounded vacuum pipe if you use dust collection, movement in your USB cable (e.g.: you moved your computer) or something else that created an interruption of the communication port. Following this, did you have to rehome and everything worked?


That is a good point that to two might not be connected. What ever the issue was it doesn’t seem to have been anything permanent. I’ll try running the part again this week.

I think thats a solid point I didn’t consider about EMI, as well I have been meaning make some heat sinks for my nomad. I just finished making a pretty solid sound suppressing case for it, with built in climate control which was working really well. The heat sink is next on my list after finishing this current project.

I do have an air nozzle for chip clearing, potentially a static build up from the rubber/plastic tube rubbing against itself as the spindle moved back and forth?