Lots of 3D printing problems stem from plastic oozing out of the hotend, as everything warms up and the plastic becomes soft and begins to flow, gravity takes hold and molten plastic can ooze out of the hot end.

Hal Tucker from Cliffhanger sums up the problem perfectly with his line “Gravity’s a bitch, ain’t it?”

A photo of an oozy lumpy 3D print

One of my first, terribly lumpy ooze-tastic prints

Oozing before printing:

When bringing your 3D printer up to temperature (180°c for PLA), and your printhead is not all the way down on the z-axis and resting on the build platform. You can have a bunch of plastic ooze out even before you start printing. Then when the print does start, you end up with no plastic coming out of the hotend for the first few moments of the print.

Solution: This is less of an issue these days as most gcode generators will actually make sure that the printhead is in the best position before cranking up the heat. However if you find yourself manually preheating and missing out on plastic at the start of the print, an easy little fix is to ‘prime’ the hotend by manually extruding a bit of plastic. Keep hitting the extrude button a couple of times till you get a consistent flow out of the hotend. Clear away the excess waste plastic, then quickly start the print before you run into more oozing.

Oozing while printing:

Oozing problems that occur during printing include lumps or blobs in the walls of your print and little strands (like spiderwebs) being left behind as the printhead jumps from one part of the model to another.

Solution: These problems are usually resolved by tweaking the settings in a gcode generator like slic3r. The first setting you want to tweak is temperature, most of the time oozing problems are because your hotend is running a little hot. Try lowering it a couple of degrees and try again. If that doesn’t completely alleviate the problem, another group of settings worth tweaking is retraction. You will find this under the Printer tab when in expert mode.

Retraction is where your printer will actually wind the extruder backwards when jumping from one place to another. This creates a small amount of suction to counter gravity and briefly prevent oozing. Try increasing the retraction length (how many millimetres are wound back) and the retraction speed.


  • 2015/11/15 - Increased image resolution and updated how to set retraction settings in slic3r.


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