9 Ways to avoid ABS Curl

Marvin the 3D hubs mascot
Marvin, the 3D Hubs mascot

I’ve opened up my very own 3D printing hub through my able friends at www.3dhubs.com.  To do so, I needed to print their test object, the marvin.  Oh my word! for such a little guy, he gave me some big challenges.  Those nice rounded features with sharp detail in the front, overhangs underneath and in the eyes, plus that tricky top loop.  This was a deceptively fiendish print.  3D Hubs sure know how to pick-em.

My collection of ignominious prints is growing, and I have four of Marvin’s lesser siblings on my desk as proof.  They’ve variously curled off the print bed, been knocked over mid print, overflowed at an overhang or shrunk in sections. With a bit of research and trial and error, I finally produced a print I was happy with.

Here is a list of simple fixes I’ve used to improve my print quality:

1. Level your print bed – The first step to a good print, is a clean and level print bed.  If you’re having troubles with curling on the bottom layers, re-level your print bed.  There are some useful tutorials out there.  All you need is dextrous finger tips and a piece of regular printer paper.

Here you can see the seam up the left side
Here you can see the seam up the left side

2.  Seams – Know where your printer places it’s vertical seam and orient your objects accordingly.  As the printer moves from one layer to the next, it creates a small anomaly in the corner of the print.  This creates the illusion of a seam up the side of your print.  It can be completely unnoticeable when placed on a corner or along a natural vertical line, or it can be a gross deformity on the face of your Marvin… Details which are along the seam line can become bubbly or poorly articulated as the filament doesn’t have time to set in place before the head moves off in a different direction. My flashforge puts the seam up the front left-hand corner, so I have to turn my models around in my slicer so that the seam is least visible.  In this case, up the back.

IMG_4747
The top of this pawn should be a nice round ball, instead it looks like a melted icecream

“Every printer will have a settings sweet spot”

3.  Layer time – Each layer you print, the filament needs to cool and set before the next layer is added.  This is especially true where overhangs are concerned.  My printer will handle overhangs very poorly if the object is small.  This is because the time between layers is quite quick. Too quick for the layers to set, so I end up with a spongy outcrop of gooey filament, trying it’s best to form an overhang.  Each time the print head goes back around, it pushes the gooey print back down, but it just curls straight up after each pass.  Where possible, edit your gcode to increase the time between layers.  The layers will set much better and your overhangs wont be so gluggy (yes it’s a word).

4. Multi-tasking – If editing gcode isn’t your thing, a cheeky way to force more time between layers is to print more than one object at a time.  To print my final Marvin, I added a thin tube the same height as Marvin to the opposite corner of the print bed.  This forced the extruder to travel the diagonal distance of the print bed between layers.  Yes I now have a useless tube, but it took next to no filament to produce, it was stable enough not to fall over and ruin the print, and it resulted in a tidy little Marvin.  If you have multiple jobs, try to print them simultaneously, they’ll have greater cooling time between layers and should all be better quality.

“Print quality has an inverse relationship with print time”

IMG_4750[1]
Supports generated by Replicator G. Did not snap off, were messy and filing the nubs down took a long time
Supports generated by Makerware.  Snapped off easily and didn't leave scars on the print.
Supports generated by Makerware. Snapped off easily and didn’t leave scars on the print.

5. Supports – There are good and bad supports and only practice will teach you this.  It really is a case of horses for courses.  You can see here two examples of auto-generated supports for the same object.  There are occasions where auto generated supports fail. If you have the skills, I think designing your own supports would be desireable for tricky prints.  More on this once I’m better at 3D modelling.

6. Print temp – Some forums suggested that the saggy overhangs might be caused by extruder temp being to high.  I think this is partly true and I tinkered with the temp to acheive my optimum Marvin, but increasing the time between layers was more effective than lowering the print temp.

7. Enclosed print volume – Because ABS likes to shrink as it cools, a stable and warm build environment helps to reduce the shrinkage.  My once pristine Flashforge, is now covered in patches of blue painters tape where I’ve covered up the gaps.  There’s still the top opening for the filament and wires, but I’ve tried to enclose it as much as possible.  Where the enclosure temp really stood out as a problem was on my sacrificial tube print (see multitasking above).  the bottom 3mm is all sucked in, presumably because the enclosure temp was lower in the first 10 minutes or so of the print.  Once the enclosure reached a certain temp, the shrinkage stopped and the tube returned to it’s intended diameter.  had I not printed a tube like this , I may not have noticed it.

8. Print speed – Again, print quality has an inverse relationship to print time.  You can print fast and a bit rough, or slowly and smoothly.  Every printer will have a settings sweet spot and it might change between filament brands and over time.

9. Infill – I don’t usually think too much about infill, and when we do it’s usually because I’m bemoaning the filament it will use up.  BUT Infill can serve a useful purpose when you’re printing overhangs.  I bumped up the infill to 50% on a pawn print and I was able to reduce the curl on the bottom layers of the sphere.  The extra infill served to push out the shell layers just that little bit more.  I pressume a solid infill would produce even better results.

Print with me here

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6 thoughts on “9 Ways to avoid ABS Curl

    1. Hi David,
      Thanks for your kind words and for the share on 3D hubs. I’m glad you were able to use some of my tips. All the best with your hub and your printing dreams

      Like

  1. Nice info! M a new owner and have a billion questions:) Like is there a variable in the gcode that I can change to change the thickness of outer walls or was that set in the model? I downloaded a swan stl file and printed it, it was hollow (10%) fil and the outer shell split open a tiny bit in a couple random spots, I was thinking the outer walls were too thin?

    Any help is appreciated:)

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    1. Hey Rod, your wall thickness is set in your slicer software. I use Simplify3D because it slices fast and gives a high level of control over the settings. Makerware is the best of the free slicers I’ve tried. Just increase the number of outer shell layers. I’d also break out the calipers and see if your filament is less than 1.75mm or perhaps you need to add 5% to your extrusion multiplier in the slicer to improve your layer adhesion. It sounds like an underextrusion problem.

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