Dangerous failure condition on the nomad 883 pro?

Halfway through a job the nomad 883 pro spindle turned off with no warning. Possibly due to overheat ? Luckily I looked at it around 1 minute after it took place and I saw it was still pushing the bit into the piece.
Shutting the job off and turning spindle on/off manually did nothing.
After around 5 min it started working again.
Should carbide motion not have detected spindle not spinning and killed the job automatically ? it seems a very dangerous thing to have the job continue and destroy the bit/spindle.

There is no way for carbide motion to tell this. It won’t be likely to destroy the spindle, the bit will break off first. Yes, you’ll likely destroy the workpiece. Welcome to one of many kinds of milling crashes.

This is one of many reasons you’re not supposed to leave a job unattended. This is what the e-stop is for (on recent pro’s, that means the power switch on the front of the box) If the controller is in the middle of a long command (a long linear move across the workpiece for example) there really isn’t a way for the controller to be told to stop in the middle of the command, at least not in the current GRBL being used.

This is an electromechanical device. This isn’t dangerous in the sense of it reaching out and ripping off your arms or something, but it is a hazard. Just like you shouldn’t stick your finger into a saw blade to tell if it’s running, you shouldn’t be sticking your hands in the work envelope with the machine running.


it cant tell if the motor is spinning or drawing current ? seems like an obvious sensor for this should be in place, no ?
if a cheap computer fan can report RPM shouldnt the spindle motor be able to ?

I don’t believe that Grbl has the facility to receive such a specific report so as to act on it. It is seriously memory constrained by the Arduino — look for that to be alleviated somewhat when it becomes an option to run it on more powerful CPUs — there’s been some discussion of that.

The idea of building this in as a circuit somehow is an interesting one, though it would add yet another potential point of failure, and something else to troubleshoot the problem is, you’d need to know when the spindle was supposed to be started up and when it ought to be shut down.

There is a hall sensor on the motor, and it appears to be used by a small micro on the spindle driver board. As far as I can tell, it goes nowhere else. The driver IC receives a PWM signal from GRBL to indicate what speed it wants, but there really isn’t any useful feedback to GRBL. There is a !FAULT signal, but I don’t know what they do with it (looks like nothing)

I’m not saying it wouldn’t be possible to design something that would detect the condition, or that it would be extremely expensive to do so, but I am telling you it doesn’t appear to have this capability today. I’m not a carbide employee, I’m not their representative, I’m just a random guy, so take that for what’s it’s worth.

I’m not sure what you would expect to do what that knowledge though - if the spindle driver is overheated, or the spindle is stalled, given the time it takes to actually stop motion, you would break the mill anyway in many cases, and there isn’t anything you can do to avoid the failure besides use more reasonable speeds/feeds, certainly not anything you’ll change right before it stops when you get some warning and destroys something anyway.

GRBL is open loop, that’s just the way it is, faults and all. It does some great work for a few dollars that would have cost thousands to even think seriously about 10 years ago. That Carbide built such an accessible tool around it is really pretty great. There are always improvements that can be made.

The driver will shut down on overcurrent, and the only way to promptly restart it is to power cycle it. You’re welcome to read the datasheet on the driver IC itself, it’s a TI 8312 ( http://www.ti.com/product/drv8312 ). It’s one of two or three VERY common drivers used for this power rating. They all work basically the same.

1 Like

a simple non contact usb tachometer could be used to provide RPM if carbide motion supported it. shutting down the job would be enough to prevent a lot of damage.
<$100 for a non contact laser tachometer with usb output off the shelf.
is there any way to pause the carbide motion job from a windows command line without using the gui pause button ? simple batch script can monitor usb port and signal pause.

hmm…looks like i can do it with UNI-T UT372 Digital Laser Photo Non-Contact Tachometer Wide Range USB Interface for $50 and autoit v3.

I believe sending a ! will cause a feed hold — the problem is, it will want to decelerate the machine so as to maintain a known position when stopping which likely won’t save the endmill from breaking.

There’s also the A1 pin which may be a hardware way to achieve the same thing — would it result in a sufficiently faster reaction time?

Some notes on this sort of thing at: