Infill Colliding with other infill lines

[mechman29 0]

Hi Everyone!

 

When I print something that has an infill, the nozzle cuts across the previous infill and collides with it and snaps it. It doesn't lay down a blob, but hits the previous line. I can hear it running into and snapping the previous line. I have watched many videos where infills are perfect, yet mine are all snapping as the nozzle crosses it. What in the heck am I doing wrong? I use Cura, I have a Ender 3 v2. Using PTEG. Bed at 70 and nozzle at 250 (recommended on roll of PTEG).

Can someone help me figure this out? I'm sure it's a Cura issue within my settings. Or, maybe not! HELP! I've included a pic to show you what I am talking about. I'm a noob, so if you need more info, I'll post it asap. 

[gr5 2,178]

I've seen this before with PLA.  It usually happens when I print too fast.  It can sometimes be improved by over extruding but mostly it's fixed by slowing down.  Try printing the infill at 1/2 or even 1/4 speed you are printing now and see if that helps.  I haven't had this problem with PETG but maybe I print too slow to see this.

[mechman29 0]

Thanks for the reply! 

I just did this same test with it going at 60% speed. Same result. It's actually dragging across the previously laid line and colliding with it and snapping it. I don't understand what's going on. I have watched videos of people printing fast and not having issues. 

[gr5 2,178]

Yes I'm familiar with the "dragging across lower line and snapping".  I've seen it many times.  Cura tends to make infill at like 2X printing speed so I'd try even slower - 20% - just to see what happens.  Also you want the fan as low as possible but still turning.

 

Check your infill line width!  I didn't think of that - but cura can do some really stupid things like setting that to a different value than the rest of the print.  Make sure it is the same as your normal line width.  Or wider.

 

 

It could just be a bad brand of filament?

 

Different types of plastics have different characteristics.  PVA breaks like this very easily but PLA sticks to itself better (like a liquid rubber band) and doesn't snap easily.  PETG is somewhere in between.  Maybe your formulation isn't so good. 

 

Anyway, using the front panel on your printer, I would consider increasing the temp by 5C, slowing to 20 or 30% lowering fan, increasing flow by 20%.  If any of these work then you can put these into cura.  Infill speed can be set differently than other printing speeds.  In cura you wouldn't increase the infill "flow" (because that's not a setting) but you can achieve the exact same result by increasing the infill line width.

[geert_2 557]

My brand of PET does not like traveling through the air, not for bridging, and not for crossing gaps to the next part. There are two problems:

 

1) It does not pull a nice long string for bridging, contrary to PLA: PET tends to snap and scroll back onto its own, like a rubber band that snaps. This causes a blob hanging on the nozzle, instead of a bridge.

 

2) When liquid, PET is more rubbery than PLA. So, when crossing gaps, the pressure does not release as fast in the nozzle, causing the nozzle to leak a bit more while traveling over gaps.

 

In both cases, the blob hanging on the nozzle is deposited onto the next wall that it encounters, creating a sort of "insect antennas". See the pic below. But I could imagine that if that blob encounters a thin perpendicular strand, as in your infills, it would hit that, and maybe snap it? I am just wildly guessing, because I have never seen that myself...

 

Using a magnifying glass, try having a very close look. Maybe you can see what happens? (And if you find out, let us know.)

 

Photos:

 

Close up of "insect antennas":

 

Next to a ruler (mm and cm):

 

[mechman29 0]

On 2/21/2021 at 7:38 PM, gr5 said:

I've seen this before with PLA.  It usually happens when I print too fast.  It can sometimes be improved by over extruding but mostly it's fixed by slowing down.  Try printing the infill at 1/2 or even 1/4 speed you are printing now and see if that helps.  I haven't had this problem with PETG but maybe I print too slow to see this.

Hi! Thanks for suggesting I slow it down a bit more. I did that and it does seem better. I cut my infill back to 30 mm/s or lower and it seems it has helped a LOT! I also raised the temp up a few degrees. I was printing at 240c, and now at 245c to 250c. Here's a pic of my print at 245c. 

Obviously, it's not perfect, but it's a LOT better. I'll have to do some more tweaking to get it right on the money, but at least I'm closer!  

[geert_2 557]

I don't see any underextrusion or broken lines any more. A couple of blobs and what appear to be "insect antennas" (at the right, but hard to identify in this picture), which is what you can expect with PET in my experience.

 

[gr5 2,178]

I think something is wrong with your printer that you have to print so slow (well 30mm/sec is not so bad - that's typical of my printing speeds but I've also printed at 70mm/sec and faster).  I mean you can just keep printing like this but I think your feeder might be relatively weak (compared to most Ender 3 printers).  Maybe there is something on the feeder to tighten?  Or some other issue.

 

EDIT - I forgot this wasn't PLA.  I print a lot of PETG but not enough to feel confident what speeds are normal.  It may be you need to print a little hotter (which makes the filament less viscous).  30mm/sec might be the best you can do for PETG - I really don't know.

[GregValiant 1,268]

When you use a "Grid" infill then there are a lot of crossings.  Using "Lines" keeps them from crossing as each direction of lines is on a different layer.  If you are counting on infill for structural strength the broken lines are a problem  If you are just counting on the infill to hold up the roof above, then it likely doesn't matter.

 

I agree that PETG is much better when printing slower, and your temps are right about where I print.

 

@gr5 mentioned an adjustment...The extruder on the Ender does have an adjustment for spring tension.  It is the screw on the inboard side of the spring.  If you have the stock plastic extruder I would advise to leave the tension alone as that arm on the stock extruder is prone to cracking anyway.