Printing stops for unscheduled (& unwanted) filament change,

I just got an Ender 3 Max. The first couple prints came out good, then it started stopping for filament changes. When it is restarted several lines are missed and the item is no good. My last printing was 22 hours and the printer stopped 9 times. The finished item was in six pieces because of the missed lines. I tried two different filaments (just in case one was defective). I don’t know what to check next. Help!

I am guessing it is not actually out of filament?

Could you be inserting a filament change command accidentally with your slicer? What slicer are you using?

My first guess is that the sensor or wire leads (most likely IMO) are bad. If it is brand new you should contact tech support and report the issue. if it is the wiring harness or the sensor they should be replacing them under warranty.

Does the light on the sensor change colour when this is happening? (does the ender have a colour changing light on the run out sensor?)

You could try a print test and just put a scrap of filament in the sensor and see if it happens.

You could also try while that is going on manipulating the wires from the sensor it might help to isolate the issue.

Also check the wires for damage at least what you can see.

Have you done any mods to the printer?

I’m not that familliar with the Ender 3 Max, but I’ll bet it has a filament runout sensor. Those things are notoriously finicky. Some models (of sensor) have a small adjustment screw that allows you to set the minimum diameter needed to trigger it. On other models, the “sensor” is just a metal tab on a switch. You can bend the metal tab (slightly) toward the filament to make it less sensitive. There are so many better ways of implementing it that what is commonly used. If it was my design, I’d use an optical sensor. It’s much less finicky than a mechanical switch, but, of course, it’s more expensive. Have you ever looked at how the paper detectors are implemented in a laser printer? Same concept.

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As @LEGOManiac said, there are a few types of filament sensors. One of the common ones are simmilar to the microswitches used for endstops. Ive also heard some people needing to bend the tab a little bit to make more consistent contact. That being said those types of sensors are cheap, and there are “fancier” types out there.

You could try printing a “tall” object like a cylinder or something, maybe 50mm. Nothing big, just big enough to not fall over. See if its trying to do a filament change at simmilar heights as your 22 hour print.

Thanks for your input. I am obviously new to 3D printing.

The last project was 14 cm high. Printing stopped at 0.3 cm, 1.0, 2.5, 3.0, 3.4, 3.6, 4.0, 7.0, and 13.0 cm.

I used two different spools of filament - both were the same size, PLA 1.75, from 3D printing - nothing fancy - just one black and the other grey.

The project before this one was 10 cm high and had two fails - one at 5 cm and the other at 8 cm.

I will try to contact the company on Monday. The printer is only a month old.

Yeah, go through warranty while you can. If things done make sense, or somehow are not under warranty, feel free to ask away :).

Personally I have never seen a sensor fail then be ok then fail over and over. that to me sounds like a slicer error or bad cable with an intermittent connection.

filament sensors fail all the time but they usually fail and never work again unless they get taken apart.

This isn’t actually a sensor failure. The switch is simply not being pushed far enough (ie. the switch is too far from the filament). If the filament width varies between (let’s say) 1.73mm and 1.77mm and his sensor is 1.74mm from the filament* then it will register the filament as present except at those few occasions where a 1.73mm section of the filament passes by.

  • What I mean by this is that switches have an internal spring that is supposed to snap the switch between open and closed states and make it harder for the switch to change states. This limits internal electrical arcing and switch bounces (the repeated close-open-close of the contact as one metal contact plate literally bounces off the other). In this case the switch is mounted far enough away that it’s near the spring’s center-point - roughly half way between where the spring wants to hold the contacts open and where it wants to hold the contacts closed. At the center of that “hump”, even a slight movement will cause the contacts to change states but the movement isn’t large enough to permit the spring to do it’s job. He simply needs to move the switch, or at least the metal tab on the switch, 0.05mm closer. If you ever dabble in robotics, you’ll come across this problem frequently.
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take the sensor out of the equation. put a filament end in the sensor and by pass it. If it behaves normally replace it of tinker with it. They are 9-20$ I’d just replace it with a higher quality version.

If it still does the same it is not the sensor.

Then try a print that is pre sliced. If it doesn’t print fine check the wiring.

One variable at a time.

Sensor Gcode then wiring.

Lego, my first one i ever bought 3 years ago does not have a spring inside. I dropped it off my desk searched for almost an hour before I noticed it stuck on the steel leg.

The Prusa also uses magnets. It has a pair of rare earth magnets. When the filament is passed inside a arm moves to interfere with an optical sensor.

The Orginal sidewinder one who knows I didn’t bother with it, the path was not clear no filament would enter it. I bought a replacement is a magnet. I have also seen one at work that uses a circular encoder.

If it is a spring it might work. Two of mine are glued shut you would have to break the case to get inside and rebuild it. I am working still, and caring for my elderly dad. I personally do not have time to spend hours fiddling with a sensor that costs 9$. You could be right or wrong. My suggestion is to check things before messing with taking things apart and potentially voiding the warranty.