When printing an object that has slanted surfaces without support material under it, chances are you have seen some pretty bad results with these overhangs. This usually happens when trying to 3D-Print overhangs exceeding an angle of about 30-40 degrees. The print will start to curl upwards and because the following layers are then also printed upwards, it will become an exponential problem.
"Cooling is your friend"
The speed of the cooling fan has the most influence over the bad overhangs. 3D-Prints that are not susceptible to warping require the fan speed to be set to 100%. By cooling down each layer before the next one is deposited on top of it, reduces the chance of the first layer to curl upwards.
In the above picture, you can see the difference between cooling at max (right) and without cooling (left). You can click on the picture for a better image.
The nozzle temperature is another important factor when it comes to preventing bad overhangs. The lower the nozzle temperature, the better. A lower nozzle temperature means that the liquid plastic is closer to its solid state meaning a shorter solidifying period is needed. This, however, is quite tricky because you cannot lower the nozzle temperature too much because it will lead to under extrusion because of the plastic not liquefying fast enough. Learn more about: Under extrusion.
Left has been printed with PLA with a nozzle temperature of 220 oC and right with 205 oC. The difference is not great but every small tweak helps.
"Low nozzle temperature & high cooling fan speeds"
If you apply this rule of thumb to your 3D-Prints with large overhangs then you’ll get the best results. If you have the opportunity, you could also make a flat crossing instead of an angular surface as shown in the picture below.
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