Overhangs and bridges are some of the most challenging geometries to print with high quality on a 3D printer. Beyond hardware cooling improvements and model modifications, here are three slicing tips which may also improve overhang quality when printing with PLA.
1. Lower Bed Temperature
For poor quality overhangs near the bed surface, the bed temperature itself may prevent the material from cooling adequately.
Symptoms: Poor quality overhangs 5-10mm up off the bed.
Solution: Lower bed temperature by about 5C to 50C or 55C. If concerned with adhesion, use a glue or hairspray as it will greatly improve your print consistency.
2. Change Top/Bottom Shell Pattern
For poor quality overhangs higher up on the model, the Top/Bottom Shell Pattern may be causing too much localized heat. This can happen anytime the slicer encounters an area that does not have the minimum Z thickness by printing the walls alone. To fix this, the slicer will add, by default, a line or zigzag Top/Bottom Shell Pattern in that area. This will reheat the walls and cause them to droop.
Symptoms: Poor quality overhangs higher up on the model, with a lot of back and forth motion of the print head.
Solution: Change the Top/Bottom Shell Pattern to be concentric instead. With most models, this will decrease the amount of time the print head will spend in one place, allowing for more even cooling while the model walls are thickened along the Z-axis.
3. Decrease Bottom Thickness
Symptoms: Poor quality overhangs are still there, changing the Top/Bottom Shell Pattern did not affect a large change.
Solution: Decrease the bottom thickness. This tells the slicer that a thinner Z-axis thickness is adequate. This will also speed up print time.
Drawbacks: This solution should be tried last as it will, in theory, decrease the strength of your model in that area by decreasing the amount of material stuck together between layers. Increasing the infill slightly will probably help alleviate any strengths problems, along with not affecting print times that much.
Conclusion: Supports Are Not Always Necessary
If you use the above three solutions, most support structures for overhangs can be avoided. As support material is just waste, improvements in slicing technique are key to higher quality prints, higher profits, and a more sustainable environmental impact.
At PrintAPot, our design goals are to make 3D printed planters that we can pull off the printer bed and ship out without post-processing. Sometimes that means designing models with better overhangs, modifying existing models, lowering speeds, and/or optimizing advanced slicing settings like those above.