Help with a strange problem

[Duckyfresh 1]

I am printing a thick disc like a hockey puck in TPU using CURA 5.6.0. I had zero issues for a while then a problem suddenly started. It prints perfect bottom layers (8 layers top/bottom) and when it gets to the 9th layer, it also prints the outer wall perfectly (10 walls) then when it starts to print the infill (60%) the extruder starts making a ticking noise and the filament comes to a stop grinding the filament, no more extrusion happening. I tried the following to no avail in the course of 6 failed prints:

• Took out the extruder (Hemera DD), took it apart, inspected (no issues other than ground filament), cleaned (did this twice so far)

• Checked for blocked nozzle and did a couple of cold pulls (all perfect with a clean, coned shaped filament)

• Slowed the print down to 30mm/s, both walls and infill (previous successful prints used 30 wall/60 infill with 0 issue)

• Tried different retractions (originally set at 0.6mm and 40mm/s)

• Tried two different brand TPU, all fresh out the box (Creality and Overture)

• Used different versions of Cura

• Tried different infill types (triangular, grid)

• No signs of heat creep

• Extruder motor doesn't get hot at all

• All fans work fine

• Tried different print temp (previous temp that printed perfectly was using 230. 225 seems to work fine as well when printing the bottom layers)

• Calibrated e-step

• Bed leveld multiple times

• P-ID for nozzle and bed tuned

Every print fails as soon as it starts printing the infill with the same, ticking noise and filament not advancing, eventually the filament being ground up by the gear and completely stops. Here's a video several seconds after it starts printing infill.

The fact that the problem happens as soon as it starts printing the infill makes me wonder if it's some setting in CURA that I accidentally changed?

Photo of a failed print below. Thanks.

Edited April 2 by Duckyfresh

[Slashee_the_Cow 268]

If you could post your Cura project file (.3mf, in Cura get it ready to print then go to File > Save Project) that would help to see if you have any settings at less than ideal values.

• Due to its elasticity, TPU needs far more retraction than anything else I've tried (I haven't tried a huge array of materials though). I use 2mm at 45mm/s and it's still string city (which isn't so bad if it's only on the inside).
  • Try to minimise the number of retractions, forcefully using Travel > Maximum Retraction Count and Minimum Extrusion Distance Window if you have to. It can and will be chewed up by the extruder if you retract too many times.
  • A longer retraction distance is probably better anyway because it means any degradation from going back and forth through the extruder isn't focused on a single, short area. 
• Make sure you're not trying to print the infill too fast: whenever I print TPU I do the whole thing at 20-30mm/s.
• Make sure your acceleration is not too high: if the head just zooms off somewhere at 2000mm/s² the filament is liable to remain attached to its friend the nice warm nozzle instead of the not-so-warm model which can cause things to get blocked up.
  • Same applies to jerk.
• Don't reduce your flow: At low flow rates due to its malleability it can be hard to feed properly, even with a direct drive extruder.
• Try turning on Infill > Connect Infill Lines: this will significantly reduce the number of retractions doing infill.
  • The Cross and Cross 3D infill patterns are great because they are drawn as continuous lines, but they leave large air pockets (which is great if you want squishy, but enough walls and skin will probably negate that if you don't).
• If your filament has been out for more a few days you should consider drying it.
• I can personally vouch for Overture TPU.

[Duckyfresh 1]

Thanks for the awesome reply!

I already see some of the things that I can try on my end. I had a feeling that it's somehow related to retraction/acceleration and you've given me enough to test some settings. Hopefully I can report back with good news!

[Duckyfresh 1]

15 hours ago, Slashee_the_Cow said:

If you could post your Cura project file (.3mf, in Cura get it ready to print then go to File > Save Project) that would help to see if you have any settings at less than ideal values.

• Due to its elasticity, TPU needs far more retraction than anything else I've tried (I haven't tried a huge array of materials though). I use 2mm at 45mm/s and it's still string city (which isn't so bad if it's only on the inside).
  • Try to minimise the number of retractions, forcefully using Travel > Maximum Retraction Count and Minimum Extrusion Distance Window if you have to. It can and will be chewed up by the extruder if you retract too many times.
  • A longer retraction distance is probably better anyway because it means any degradation from going back and forth through the extruder isn't focused on a single, short area. 
• Make sure you're not trying to print the infill too fast: whenever I print TPU I do the whole thing at 20-30mm/s.
• Make sure your acceleration is not too high: if the head just zooms off somewhere at 2000mm/s² the filament is liable to remain attached to its friend the nice warm nozzle instead of the not-so-warm model which can cause things to get blocked up.
  • Same applies to jerk.
• Don't reduce your flow: At low flow rates due to its malleability it can be hard to feed properly, even with a direct drive extruder.
• Try turning on Infill > Connect Infill Lines: this will significantly reduce the number of retractions doing infill.
  • The Cross and Cross 3D infill patterns are great because they are drawn as continuous lines, but they leave large air pockets (which is great if you want squishy, but enough walls and skin will probably negate that if you don't).
• If your filament has been out for more a few days you should consider drying it.
• I can personally vouch for Overture TPU.

 

I made some changed to the settings by reducing the speed even more, increasing the rectraction distance and lowering the jerk settings. It did improve somewhat and now it prints several layers of the infill, but the same problem came back after that. I would say about 20% into printing the infill, it grinds again and stops extruding. At this point, I'm thinking maybe it's the hardware issue (nozzle or extruder motor?).

 

Anyway, I've attached the Cura file as you requested. Thanks!

CE5_puck.3mf

[Slashee_the_Cow 268]

This is the kind of problem I hate: not one of the 90% of problems which solve themselves. And of the remaining 10%, it's not one the 9% which have an answer which seems blatantly obvious when someone points it out to you.

(That is to say that it's got me a little bamboozled)

 

The main things that are striking me as "different to how I do TPU without a problem" are:

• Print temperature: You have it at 230°. I run mine at 220° - probably worth a try
• Cooling: You have the fan turned off. I have mine turned on at 100%, initial speed 0%, regular speed at layer 4 - do this one
• Layer height: You're at 0.24mm. I almost always use 0.2mm - unlikely to make a difference when you're printing slowly enough (which you are)
• Infill:
  • I've never used 60% density, but I'm usually trying to make things a bit squishy, so this probably isn't the cause of the problem.
  • Because I'm usually trying to make things squishy I usually use the Cross 3D pattern. I very much get the feeling you're not going for "squishy". It's good that you've got Connect Infill Lines turned on (because travels with TPU are always hard)
  • Both Cross 3D and Grid (with connect lines turned on) are printed as a single continuous line without travels. The main difference is that Cross 3D never crosses itself but the grid lines do cross other grid lines. I don't know if this at all contributes to the problem, but I figured it was worth mentioning
  • Suggestion: Try using the Zig Zag pattern. The end result is similar to a grid (the holes will look smaller, but with the infill density % the same, it's going to have the same ratio of infill to air) but it prints doing horizontal lines one layer, vertical the next, so that the path never crosses itself on the same layer.
    I'm assuming the path crossing itself usually isn't a problem (or those infill patterns wouldn't exist) but I'm just looking for differences between your settings and mine and this is one of them.

Hopefully some of that might help. And remember, small scale testing is your friend: if you can make a smaller version that has the same problem, test with the small one, you'll save yourself filament and time.

[Duckyfresh 1]

Thanks again, I will try these settings to see if it will make a difference.

[Duckyfresh 1]

On 4/3/2024 at 11:13 PM, Slashee_the_Cow said:

This is the kind of problem I hate: not one of the 90% of problems which solve themselves. And of the remaining 10%, it's not one the 9% which have an answer which seems blatantly obvious when someone points it out to you.

(That is to say that it's got me a little bamboozled)

 

The main things that are striking me as "different to how I do TPU without a problem" are:

• Print temperature: You have it at 230°. I run mine at 220° - probably worth a try
• Cooling: You have the fan turned off. I have mine turned on at 100%, initial speed 0%, regular speed at layer 4 - do this one
• Layer height: You're at 0.24mm. I almost always use 0.2mm - unlikely to make a difference when you're printing slowly enough (which you are)
• Infill:
  • I've never used 60% density, but I'm usually trying to make things a bit squishy, so this probably isn't the cause of the problem.
  • Because I'm usually trying to make things squishy I usually use the Cross 3D pattern. I very much get the feeling you're not going for "squishy". It's good that you've got Connect Infill Lines turned on (because travels with TPU are always hard)
  • Both Cross 3D and Grid (with connect lines turned on) are printed as a single continuous line without travels. The main difference is that Cross 3D never crosses itself but the grid lines do cross other grid lines. I don't know if this at all contributes to the problem, but I figured it was worth mentioning
  • Suggestion: Try using the Zig Zag pattern. The end result is similar to a grid (the holes will look smaller, but with the infill density % the same, it's going to have the same ratio of infill to air) but it prints doing horizontal lines one layer, vertical the next, so that the path never crosses itself on the same layer.
    I'm assuming the path crossing itself usually isn't a problem (or those infill patterns wouldn't exist) but I'm just looking for differences between your settings and mine and this is one of them.

Hopefully some of that might help. And remember, small scale testing is your friend: if you can make a smaller version that has the same problem, test with the small one, you'll save yourself filament and time.

 

Finally found the problem and fixed! It was the tension on the filament extruder gear. Apparently it was too high and perhaps squeeziing the filament too much that resulted in getting the filament kinked and ground against the gears. I'm not too sure why the problem would happen after printing for a while, maybe the heat gradually makes the filament softer as it travels up and makes it more pront to kink? In any case, I can now print with my original settings of 230C, no fan, 0.6/40 extraction, 0.24 layer height, 60% grid infill. Thanks again, @Slashee_the_Cow, for helping me diagnose the issue!