Splitting and gaps in prints

Hi there

This problem has been bugging me for a while now and I have been working my way around it by making up an acetone and abs goo mix and filling in the gaps and sanding it down but it is becoming impractical to continue doing this.

As you should be able to see from the cylinder object there is splitting in the sides like the layers are separating, this only happens on tall objects that I print.

The biggest issue I have and the one I really really want to fix is the gaps in the tops of some prints, I have no idea what is causing it and have fiddled with the settings a lot in an attempt to fix it, sometimes adjusting the models dimensions helps. I do quite a lot of prints that are similar to the two shapes you see there and sometimes I get gaps and sometimes not. All the 3d models are single solid meshes. Print material is ABS.

To clarify I print a lot of different shapes on top of a little block as shown in the pics, sometimes I get gaps as shown.

The same object works sometimes and sometimes doesn’t?

Are the ambient conditions changing (warmer or colder room, breezes, etc.)?

Same object produces the same results (on the gaps on top), but I print a great variety of objects and some work some don’t and I can’t see a common factor between them to determine what exactly causes the problem. Adjusting the line thickness (of the actual 3d model) will sometimes fix it but often that is not always an option. Room temps are pretty much the same give or take a few degrees and no breezy conditions.

If I look really closely at the object it looks like it prints the walls and then tries to fill in the top in between the walls rather than putting a lid on it once the walls are done. Another thing to note is that regardless of the infill % it still does it. I usually print at 20% infill but have tried 100% before with no change in results.

(to clarify in regards to the 2 images above, both are the same model but one is 22mm x 22mm and the other 33mm x 33mm)

It is a result of the nozzle size and the width of the part right there. If the nozzle is a 0.5 MM size and the width is 1.3 MM then that is 2.3 nozzle widths which it really can not do. so it leaves a small gap due to the size of the part right there. You could try to set a different nozzle size while slicing the part to cure that, but that brings up other printing problems that may be harder to cure. :frowning:

I’ll give that a go, as you say though it may cause over or under extrusion but we shall see.

Would using the “Tweak at Z” plugin to bump up the flow rate just for the top layers help fill in those gaps on the top? You would still have some over extrusion, but at least it would not be through the whole print.

If I knew how to do that I would lol.

Are you using Cura? If so, in the “Expert” menu, choose “switch to full print settings…”. If you were using “switch to Quickprint” settings, it will ask you if you want to copy the settings. Choose yes. Choose the “plugins” tab at the top of the left column. Choose “tweak at Z” and then click the down arrow just below the plugins choices. You can set a height in mm or choose the layer where you want it to apply the tweaks. I have not used this before, but you could try bumping up the general flow rate to something larger than 1 (1.1 or ??) and see what happens.

It’s possible that bumping up the flow rate will cause you other problems, but worth a try.

I will give it a go as soon as possible and let you know the outcome, should be interesting at the very least and yes, I am using Cura.

The splitting / delamination of layers is due to poor layer adhesion. ABS contracts as it cools which contributes to the delamination. Try turning off cooling (fan) or limit cooling to 50% and try extruding 1-2C higher. No fan means the ABS will cool “naturally”, increasing the extrusion temp will increase the amount of time the extruded filament is molten… promoting adhesion to the previous layer. For eSUN ABS, I like to print between 243-245C

If you can, build an enclosure to trap heat. A blanket over the machine will work in a pinch, just make sure it doesn’t interfere with the hotend.

Hope that helps!