CM crash leaves spindle spinning, loses machine zero

Software
1

Well, this one was quite odd. Never seen it before. I left my Nomad running unattended for a few hours, and came back to find that CM had crashed with a Windows pop-up: "Carbide Motion has stopped responding and must be closed."
Okay, these things happen. But the disturbing (and possibly dangerous?) part was that the spindle was still going at full rate, touching the stock, with the axes all frozen where the Nomad had been when CM stopped.
The weird part was that, when I rebooted CM and tried to re-run the same GCode file, without re-zeroing (I couldn’t anyway – I’d zero’d to the top center of the stock, and it wasn’t there anymore), the Nomad had completely lost zero – in fact, the table went right to the back end and started cogging the stepper motor (isn’t there a limit switch at that end?). Now, as far as I was aware, the machine zero is stored in the GRBL board, so crashing and/or rebooting CM should have no effect on it, yes? The Nomad was not rebooted, just CM.

So, I dunno – I mean, nothing caught on fire from the spindle burnishing the same bit of the wood for hours. But was there a risk? At the risk of being the “how hard could it be?” guy, I have to wonder if perhaps having the firmware stop the spindle when there’s a communications timeout would be a good safety feature to have.
The Zero loss is more puzzling, but less worrying – I can always throw in another block of wood and re-run the job. But it does run counter to what I (thought I) knew about the Nomad’s firmware workings.

2

Rob indicated in another thread Nomad is fantastically accurate and repeatable! that the machine zero is stored in the control PC and not locally in the Nomad.

3

Yeah… I literally just read that thread, after posting this one. :scream:

Although… that does leave me wondering how the zero got lost, still. Wouldn’t it have been saved at the time it was set? Possibly the way that CM crashed wiped out or corrupted whatever file CM saves that data to?

4

Other programs I use save ini type of data upon exit, and if CM is like that and crashed in an unexpected way it didn’t get a chance to write the current machine zeros. In my case, it was communication with the Nomad that failed and I did an orderly shutdown and reboot of the PC so I gave CM a chance to write the zeros. Just a theory… On the other hand, SOP might be to save the new machine zeros each time you exit the Set Zeros screen so I can argue against my own theory. :slight_smile:

5

It is critical that one never leave a CNC machine unattended. This is considered a serious safety violation. Minimally, one should be in earshot of the machine - with practice one knows their machine and when the sound “goes off”. Ideally, one should be able to see the machine running.

In the best case, a crash simple breaks your tool and you loose your piece. A more serious crash can take out your spindle (probably not able to stop this but just maybe one can). In the worst case you start a fire.

I personally know two home CNCers who had a fire - one lost a detached garage, the other their house.

I’ve seen fires start in commercial settings, even though the machine was really never unwatched (a bit far away from it though). The fun one was the plenum of an expensive vacuum system. MDF top. Burned underneath the piece and the airflow stoked the burning. Serious smoke in seconds, even in the 15 seconds it took to the get to the machine and hit the E-stop. We had to yank the sheet off the top and do some serious fire extinguisher action until the fire department arrived (the alarms went off).

Obviously wood and plastic are the easiest material to have a fire with but it can happen with some metals as well. A spindle that crashes into stock and spins long enough can generate quite a bit of heat.

It doesn’t matter that the Nomad has a small spindle that may be easy to stop. Please don’t develop bad safety habits - stay near your machine. Something like a baby monitor will work… but not the best solution.

1 Like
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Not wild about the baby monitor idea, but otherwise agree.

It kind of worries me that the machine operating checklist is on the second page when sorting by popularity:

http://docs.carbide3d.com/article/41-machine-operating-checklist

Similarly, the matching page on the wiki: http://www.shapeoko.com/wiki/index.php/Operating_Checklist has only been accessed 5,348 times (as of just now), but there are perhaps twice that many machines in the wild.

1 Like
7

I hear what you’re saying on unattended running, although I still maintain that shutting down the spindle in the event of a communications loss is a very basic safety feature. I do industrial automation for a living, and I have to have that equipment run completely unattended for 100s of hours at a time. The Nomad isn’t that grade of machine, I know, but this is a sufficiently basic safety feature that I think the Nomad really should have it.

Beyond that, given my day job and commute (I’m home about 7hrs out of every 24, and under medical instructions to get 8hrs of sleep a night), the simple fact is that if I have to watch the Nomad whenever it runs, I’m never going to use it. Either I run it while I’m away, run it while people are asleep (too noisy), or not at all. If the spindle would stop when I pause a job, I could break up cuts across the small slices of time I can spare, but since it doesn’t, I’m stuck.

8

It may not be possible to detect that the spindle needs to be shut down. If it keeps spinning there is a lot friction and there can be a fire.

I agree that communication loss should be a virtual E-stop. However, there are software glitches, stepper failures and a host of physical things that can go wrong. Remember the vacuum deck fire I explained above?

That happened because of a bug in the G-code runner! The spindle went nuts in Z, slammed into the piece, kept spinning, ate through the stock (wood), went into the plenum, and kept spinning. Fire plus lots of forced air. Even though we were within eye and earshot, the ~15 seconds it took to get, there, E-Stop, and rip the sheet off the sheet and plenum top there was a good deal of crisping and smoke.

The Nomad is more than capable of starting a fire, even with it’s ~100W spindle. The dust kicked off from wood is highly flammable (not to mention the wood itself). Grinding the stock/piece can start a fire. A collision (e.g. fixture, screw, stock; fixture comes loose) can cause a spark in a dust filled chamber. Grinding plastic can start a fire - with cyanide and other toxic fumes.

As a general rule one must monitor their CNC - within eye sight and ear shot to have the highest safety margin. Most failures can be heard and so a baby monitor setup could work. No, it’s nowhere near as safe as being within eye sight - but it is a great deal better than nothing.

I do understand your problem. I’ve done wicked long jobs too… in an industrial setting with all the safeties (fire detection and suppression) and such. It hard when we CNC on the side. :wink:

The Nomad is generally in a home/garage setting and many of the users are new to CNC or lack a lot of experience. It is critical that we teach good habits, someday it will save someone’s house.

Oh, one should have a fire extinguisher near.

9

Just to add to this discussion, I’m one of those “new to CNC” users with a Nomad in my garage. I had a failure last night when I had left things unattended for fifteen minutes.

Photo-Oct-06,-7-55-33-AM.jpg1536×2048 948 KB

I’ve previously carved two of these guys with no problem. In this case, what I think happened was a support failure, resulting in the main object breaking free from the rest of the stock, blocking the cutter, and causing the stepper motors to skip. I’m really not certain how the steppers could have skipped that far. Perhaps a small skip resulted in a deeper dig, which resulted in more skipping, etc. The cutter snapped before I returned.

In previous cuts, if I was repeating a known successful design, I’d been leaving the Nomad unattended for hours. Needless to say, I won’t be doing any more unattended cutting. And I’ll be revisiting my design with more supports.

I keep a fire extinguisher handy since I carve mostly wood. I’ve never had to use it, or even encountered a situation where chips/stock heated up enough to be a concern. Still, better safe than sorry.

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For me, leaving my nomad unattended means sitting in the next room with my shop / office door closed. I can still hear it cutting and now know what it sounds like when something goes wrong. Even then, I go in from time to time to vacuum out wood chips.

I think it’s important that the messaging should be clear - don’t leave your machine completely unattended. It’s too risky.

That said, there have been a few times carbide motion froze up and the spindal kept spinning. I agree with others that the fail safe should be that the spindal shuts off it it loses communication. As well, I was wondering if there is a way for the spindal to cut off if the rpm goes below a certain point quickly - which is what happens if the stock moves and the cutter hits too much material etc. That way when it happens, the machine can automatically shut off.

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Darren, you are so right.

When teaching machining students, one is taught to use hearing, touch, smell, and sight. With training, one can touch their machine or hear it and know if there is chatter or a problem. Smell something unusual? CHECK! Using your senses is critical to being a safe and effective machinist.

I have students trained quickly to the sound of their machine - and boy do they jump when they hear a problem!

None-the-less, there is no replacement for eyes on. One should never depend on mechanical safety devices - no matter how good they are. Check! There is always a smarter type of failure!

Yes, we should ask Carbide3D about adding some disconnect safety mechanism.

12

…yeah, gotta get a fire extinguisher too.
I’ve got less excuse than J. Random Maker, being a heavy-machinery professional. But, as demonstrated, I didn’t treat my Nomad with the degree of caution it deserves, and I could have gotten burned. I am rather concerned about some random amateur who isn’t as lucky – if Carbide gets sued into oblivion, where will I get spare parts? :wink:
Speaking as both an automation professional and an idiot who left his Nomad run unattended for hours, I agree that a virtual E-Stop on communications loss would be a good feature to add, assuming it can be crammed into the GRBL firmware. It’s not fair that Carbide should need to idiot-proof the Nomad for mass market, but it’s smart.
And now I’ll be selfish and reiterate my desire for a Pause function that really works, including the spindle – it really would reduce my temptation to run the Nomad unattended (hint hint)… :innocent: