This problem occurs, when your infill has too weak strings and is not strong enough to support the outer shells. In that case the whole print gets low strength. Other infill pattern, more infill and a lower infill print speed can be used to eliminate this problem. A clogged nozzle can also be the problem.
Lower Infill print speed
When a bad infill or weak infill is detected, the material may be not able to get melted that fast. Try to decrease the printing speed to get a solid infill with enough plastic to support the outer shells and see if the problem is fixed.
More infill extrusion width
If the infill of the printed part is weak, the whole print becomes weak. Set a higher infill extrusion width when detecting a weak infill. This can be done by watching the part while printing.
Alternative Infill patern
If the infill of the print is weak, the hole parts gets weak and can break down in use. There are a few different infill patterns with different fill angles in the slicer settings, from which you can choose. It depends also on the printed part which pattern fits the best and supports it the way he needs.
A cold pull works best with slippery, soft materials – like Nylon filament.
Again, heat up your hotend to the working temperature of your Nylon or Polyamide filament, push it through the hotend as far as possible, ideally, until your previous material is cleaned out, which obviously is going to be somewhat hard if your nozzle is completely clogged. Then have the hotend cool down.
What we recommend is to set the hotend to 110, 120°C and just keep on pulling on the filament while the hotend is heating until the filament plops out in one piece. Then cut off the impure end of the filament, fully heat the hotend again and repeat the process until the pulled end of your filament comes out clean and you’ve restored good flow through the nozzle. Usually, two or three passes should be enough.
For this method, you need an acupuncture or hypodermic needle, so that you can try to remove the blockage. Obviously, you’ll need a needle or wire that is small enough to fit into your nozzle bore, typically 0.4 mm.
We don’t recommend using a drill bit instead, because they break more easily than solid needles and worst of all, can permanently damage the nozzle if you are not careful.
Preheat the nozzle to your regular printing temperature for each material and start poking with the needle. Be careful not to burn yourself. The goal is to break the blockage so that it slips through the nozzle. The next time you push filament through the blockage will slip through the nozzle together with the filament.
You might have to go through the cycle a few times and push through a bit of filament by hand to check if you have managed to break up the blockage sufficiently. If this method does not work for you try the cold pull method