As a newbie to the MPCNC Primo, I have just learned how important it is to check the two loose M3 screws for the leadscrew brass nut are in place before running a job! Here is a pic with the M3 screws missing…
Lots of smoke and potential fire risk ( need to get a smoke alarm)!
A lesson for all newbies
I guess what happens is the router does not get lifted between cuts/carves and over time the router goes lower and lower until the collet screw hits the job (wood in this case). Yes?
As I’ve said before, everyone gets to set their own level of risk tolerance. I think you were very lucky and got off lightly this time.
I will never leave my CNC router running unattended. I let 3D printers run overnight, and may even run to the bathroom while the laser cutter is doing it’s thing, but never the CNC router.
I’m not the “safety police” and am not in any position to tell anyone else how to live their life, but there are numerous examples of videos online showing CNC fires starting and escalating to truly terrifying levels in seconds. The combination of lots of friction (the collet rubbing), plenty of tinder (sawdust), and forced airflow (dust collection) is, quite literally, a recipe for disaster. Once the fire has started, just hitting the e-stop won’t be enough because there’s plenty more fuel already in the neighborhood.
In one of the pictures I saw, the remains of a melted smoke detector were lying right on top of the CNC in the middle of the totally burned down garage. Clearly the detector was not adequate to prevent that fire from doing possibly lethal damage. This aligns with the speed at which the other videos show the fire growing from smoke to embers to full flames.
I was literally on a ladder installing a smoke detector in my garage when I smelled smoke from my cnc in a similar situation. I killed the power, and the smoke alarm never triggered. If I had waited much longer, it would not have mattered if I wanted to stop it.
Things like fire alarms and even fire extinguishers are designed to get people out of a fire, not to stop a fire. By the time you react after being alerted, it is usually too late to reverse the progress. You use the fire extinguisher to make an exit at that point.
If you are standing there with a fire extinguisher, and you notice the fire early enough, you might be able to stop it. But if you fail, and have to get past a fire to escape, you will wish you still had an extinguisher.
Tom,
Many thanks for your reply…very informative and will take on board your advice. Thank you. Building such a fantastic machine has been brilliant but it’s scary that justone or two small inconspicuous M3 bolts not being present could potentially cause a major fire.
So far in my journey with this machine, when changing the bit/ removing the router, I have found that the M3 bolts sometimes fall out. Wondering if there is any way to fix this?
Kind regards, Carl.
The primary job of those screws is to keep the brass lead nut from spinning in the hole so that the leadscrew can lift and lower the tool attached to the Z axis. If the lead nut turns freely, then the Z axis won’t move (or won’t move the right amount) when the lead screw is moved by the stepper motor.
On my Burly I have 2 bolts (machine screws?) that go through the brass lead screw nut. They come down from above, and I believe they screw right into the plastic. Mine have never worked loose, but there can be significant tolerance issues with 3d printed holes.
If yours have come loose multiple times, I would consider using an epoxy adhesive to glue studs into the holes in the plastic (I’d just cut the head of an appropriately long cap screw) with the brass lead nut removed. Putting nuts on top would then hold the brass leadscrew nut in place. You could use nylon-insert locknuts to help keep vibration from working them loose in the future. Jam nuts (double nuts tightened against each other) could also work.
Alternatively, you could fit a cover over the area where the screws fit so that even if they’re loose they can’t lift out of the holes. This could allow some slop if the whole lead nut tried to move up when it should be lifting the Z axis, but at leas the lead nut would not be able to rotate.
Fun fact: It can start a fire even without losing any screws. Just sending it the wrong gcode or failing to set the initial Z height can easily cause the bit to auger itself. Which is why it isn’t safe to leave alone.
Not suggesting this as necessary by any means, but my plan to add a 120vac heater to my printer bed includes adding a co2 suppression system hooked to a 10lb tank. I plan to integrate that with my Cnc once it is working. A buddy mentioned that an upside down cylinder will dump cryo liquid and cool dangerously hot material before it sees oxygen again. Sounds effective for this.
