Originally shared by paul wallich How much purging does your 3D printer hot end

3D Printing
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Originally shared by paul wallich

How much purging does your 3D printer hot end need?

Before building a part out of ABS (because it has to be strong but not brittle) on my Metal Plus, I ran the hot end up to 225C and told octoprint to extrude a bunch of filament. I ran it until the clear PCTPE I’d used for the previous print stopped coming…
http://invisibleturtles.org/2015/05/15/switching-3d-printing-filament-purging-versus-cleaning

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Never hurts to clean it out with a cold pull. Also, I find that if you have plastic left in the nozzle and heat it fully, then shove cold filament in as fast as possible, it purges more effectively than if you insert the filament before heating or let the motor slowly push the new filament in (for reasons that should be obvious).

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I prefer to change filament when heating up. When it reaches 60C (for PLA) I start running the extruder backwards by hand to see if the filament is loose. If it is loose I jank it out. That normally gets the whole hotend cleaned out perfectly. If left past 60C there can be a small string of plastic inside the hotend but I have had no problems with that. Also, remember to feed new filament in quickly to avoid potentially damaging the hotend.

If hot, I purge like you described in your post. But there are often pieces of plastic stuck to the walls just inside the nozzle opening (I use a jhead) which will come out at some point. To fix that I retract 10mm and then purge, and repeat a few times if necessary.

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@Nathan_Walkner
Thanks, this is an ubis. Has worked just fine in the past as long as I was sticking to one filament type.

Everyone else: Thanks for the pull idea. I’ve been retracting after print jobs when I anticipated changing filament, but that always leaves a bunch of the old stuff in the bottom.

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The Ubis has an exceptionally long hot zone, so you should expect it to require a lot more purging than most.

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@Whosa_whatsis
“shove cold filament in as fast as possible” for confirmation, do you mean manually or via motorized feeding ?

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If you have a good release on your extruder mechanism, manually is usually faster, but it depends on your setup. The trick is to push then new filament through the hot zone as fast as possible so that it is still solid when it hits the molten filament already inside, so that it will push that out first rather than mixing with it.