What would cause these bumps on the top layer?

What would cause these bumps on the top layer? Each bump is over a infill section. Settings are top and bottom layer .8mm with 10% infill. Note that they are bumps, not dips.

That’s called “pillowing”. Best way to solve it is to add more top layers. If you use Slic3r, it also has the ability to use bridging logic for the first layer over infill, which can help mitigate this effect.

I’m just making an educated guess but since there aren’t any holes in the top layer, the heat is making the air pressure rise under the both hot and thin top layer.

Yes it’s pillowing, you need more top layers like @Whosa_whatsis said.

More layers are needed. What layer height are you using? Multiply that by 6-8 for a minimum thickness. Good part cooling also helps.

if your slicer supports it you might also increase the infill before you get to the top layers so there is less bridging.

Increase part cooling and add more top layers.

I’ve found that KISSlicer increases the infill rate 1 or 2 layers before a ceiling that dramatically reduces the pillowing effect. Making the ceiling thicker (more layers) helps too.

More infill density :wink:

you need to have at least 3 100% fill top layers, if you have make more 100% fill top layers, it will work with same settings

that is the expanding heated air pushing the molten plastic up.

Whenever I had it it was because the top layer beads were breaking when bridging across the infill below. It might be worth experimenting with layer height or temperature. I also do no less than 4 top layers, but don’t go nuts with top layers if you have a fundamental problem bridging, fix that too.

Add a pause in g-code just before top layers. Allow time to disperse some heat. Then continue.

I have made a test, set the bridging flow ratio less then 1, this setings works for me, see picture, only one layer and looks goodmissing/deleted image from Google+

@Petruse_Mihai that’s only because your 1 layer isn’t filling in all the gaps and creating a sealed chamber for the hot air to push against. However, this method seems to me like it would be effective as long as the next layers are solid.

Disable dinosaur skin in Cura. Makes a difference :wink:

I would suggest increasing the infill for starters

I vote for both cooling an be more layers