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A few minutes after finishing a print job, the filament is solidified in the nozzle and the nozzle-throat. When I start another print job a while later, the filament is not sufficiently melted and the nozzle is obstructed. Do I need to clean the nozzle after every print job ? or is there a practical method to overcome this difficulty ?

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    $\begingroup$ Which printer or which hotend are you using? This sounds as an all metal hotend problem (heat creep), or an insufficient warm up time problem. $\endgroup$
    – 0scar
    Aug 28 '19 at 9:56
  • $\begingroup$ The nozzle may be partly blocked, or your print temp is too low. When doesn’t it extrude enough? $\endgroup$
    – 09_qwerty
    Aug 28 '19 at 10:43
  • $\begingroup$ Does the hot end fan run all the time (it should)? $\endgroup$
    – Mick
    Aug 28 '19 at 15:39
  • $\begingroup$ I use a home made 3D printer and I buy the hotend in a 3D shop i.e. it's an ordinary one. Yes, it is all metal hotend. I use PLA and set the temperature to 220°C. I have an extruder fan that helps cool the extruder drive mechanism (running all the time) but I don't have an external cooling fan that is pointed towards the part that I am printing. $\endgroup$
    – Éngin
    Aug 29 '19 at 7:23
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To start a print, the printer has first get up to print temperature, re-melting the plastic in the nozzle and hotend. To get better results, it is usually a very good idea to "prime" the nozzle to make sure we have nicely melted plastic in the nozzle and pushed out the old. Some priming methods have been discussed here.

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I had this issue until I started doing the following:

  1. If you are going to print subsequent jobs (one after the other), then ensure you keep the extruder end at print temperature while you are preparing the next job. For me on my Anet A8, I'd just tell the printer to preheat for PLA (or directly set a temp for the filament being used). This keeps the heat up in the hot end and should allow you to start printing right away when everything is ready. Please note, this will usually cause the nozzle to ooze a little bit of filament as it sits. Just ensure you swipe it clean before you actually start the next print to alleviate and stringing issues when you press the "GO" button. As an alternative, you could attach a line at the end of your print which would send the G-code to keep the printer up to temperature instead of cooling off after a print is finished. If you do this, though, you have to ensure you actually do allow it to shut down when you aren't printing so as to not waste resources.
  2. If you are not going to print subsequent jobs, pull the filament out of the extruder. On my Anet A8, right after the print has finished, but before things start cooling, I will press the spring loaded part of the extruder head (the part which captures the filament against the extruder gear), then push the filament into the extruder and quickly out. This usually ensures you don't leave a lot of filament languishing in the extruder head and will make it easier to load the filament the next time you want to print.
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  • $\begingroup$ Or you could put in some Gcode right after the temperature set commands to extrude a few mm to "clear" the nozzle before starting the print. Heck, I often add a brim or skirt just to do this sort of thing. $\endgroup$ Aug 28 '19 at 15:19
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    $\begingroup$ @CarlWitthoft Skirt or Brim is, as I realized in my starting days (and discussed in my answer's linked answer), the "lazy man's priming" and can be super effective $\endgroup$
    – Trish
    Aug 28 '19 at 15:23
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    $\begingroup$ However, I'm not talking about priming, and neither do I believe is the OP taking about a priming issue. What the OP is talking about is a problem whereby the nozzle clogs between prints, which priming (or attempting to prime) will not cure. Once the nozzle cools down, the filament left in the nozzle clogs it and no amount of pre-heating, priming, or what have you, will clear the clog. The only way I have been able to overcome the clog is to pull it apart and clear the nozzle physically. Since I've been doing as I describe above, I've not had this issue. $\endgroup$ Aug 28 '19 at 15:47
  • $\begingroup$ @Pᴀᴜʟsᴛᴇʀ2 and yet, with my AnetA8 clone, I have yet to clog by way of leftover cooled filament. Maybe your hotend doesn't heat the entire nozzle? Or you're using some particular filament which leaves chemically altered (or charred) material behind? $\endgroup$ Aug 28 '19 at 17:22
  • $\begingroup$ @CarlWitthoft - I didn't say it happened every time, however, once is enough. Having to pull the hotend apart so you can print again is a PITB. By doing what I stated above, I've not had the issue again. It works as a preventative measure. I use good filament. I don't have problems when I print (in fact it seems I have far fewer than most) with extrusion or with how the filament lays, so I have to believe the hot end works just fine as far as heating. It's good you don't have any issues. That's the best anyone can ask for. $\endgroup$ Aug 28 '19 at 18:21

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