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What happens if my printer runs out of filament midway through a print?

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Sorry if this is a stupid question! I’m super new to this whole thing.

Basically I’m running a 26 hour print overnight, and leaving for work straight away in the morning. I’m worried that my printer will run out of filament (because as said, I’m really new to this and idk how much filament will even be used) midway through while I’m not there to pause it, and I’ll have to start the entire thing again and waste a bunch of plastic.

Will it just stop printing when there’s no filament left? Or have I made a huge mistake here?


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I think still fairly few hobby printers have proper filament detection systems and ways of responding to eg. filament getting stuck or running out, and so I'm just gonna go ahead and assume that your printer dosn't have this.
In which case, the answer is quite simple, the printer won't know that the filament has run out and no filament is being extruded, and so will just continue "printing" (ie. moving the printhead around and running the feeder), until it is done with the print... this will result in a model that is not fully done.
Now, depending on the material you are using and whether or not the half finished print has detached itself from the print bed, it is possible to actually reload some filament and "resume" the print...

The method is not trivial though, but it goes something like this:
- Verify that the print has not detached from the print bed (do this WITHOUT touching or in other ways disturbing the bed, as it is very important that the print stays exactly in place)

- Identify the layer at which filament ran out (eg., by counting printed layers, the more precise you can get it, the better)

- Here comes the hard part...:
You need to make a new slice of your model from the point where the previous one failed... There are several ways of doing this... From editing the gcode of the entire sliced model, to making adjustments in Cura to generate the desired code.
My approach would probably be to:
* Use the "cut off object bottom" option, to sink the print into the build plate until what remains above is what remains to be printed of your already half finished print. (you may also want to set an extra high temperature for your first layer, to make sure your resumed print bonds well to your existing failed and cooled down print, maybe even some increased flow for that layer, disable brims, skirts, rafts etc. - but you will have to do some manual cleanup of the print regardless).
* Save the gcode and open it in a text editor to edit it... You want to remove the initial z homing procedure (for this you have to make yourself acquainted with the code commands, you can read about them eg. here https://en.wikipedia.org/wiki/G-code)
* Now when starting the new print w. modified gcode, the printer won't home z... Before starting the print, you instead manually will have to adjust the bed so that the nozzle tip sits exactly at the height at which the previous print failed... Do this by grabbing hold of the printhead and moving it in over the failed print, the use small z movements to move the print bed up, until the tip of the nozzle, you should now be ready to resume the print.

- Preheat the printer and load some new filament, making sure the filament is fully primed and has begun flowing from the nozzle
- Start the print and cross your fingers... if everything goes well, the printer should home xy (but skip z), then move in and start printing on top of the half finished print...

Edited by tommyph1208

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If your printer runs out of filament, and if it does not have an "end of filament" sensor and switch off automatically, then the remaining filament in the nozzle may burn and clog the nozzle. Because it will be sitting there at hot temperature for maybe hours.


Normally Cura lists how many meters you need. Based on this, and on the weight of the spool (minus the empty spool), you could calculate how much is still left on the spool.


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