Inconsistent Extruding - Looking for advice

Hello everybody, this is my first post here. I have been printing for a few years now, with my most recent addition of the prusa i3, it has great potential. This is my first printer with a large heated glass print bed. What I am seeing is gaps or holes in the prints. What appears to happen is that the filament stops extruding (or extrudes less than it should), yet the print head is still moving around as if everything is normal.

I've checked for clogs and jams, yet this problem occurs with all my prints somewhere during the course of the print (sometimes more frequently, sometimes less frequently). I've:

• Replaced the nozzle, with no visible signs of improvement.
• Changed filament and print settings (ie perimeter speeds, infill speeds, extrusion multiplier, again with no avail.
• Rebuilt my spool and re-positioned it to prevent any additional drag when pulling filament in.
• Disassembled the print carriage to ensure that the gears from the extruder servo were aligned with the filament hole on the top of the hot end.
• Verified the set screw was tightened and that this gear was not freely spinning when trying to pull filament in.
• I do use a dust mask to clean the filament before it enters the print carriage.
• I have tried models sliced with both Slic3r (provided with Prusa drivers) as well as models sliced with Simplify3d. The same STL file prints perfectly on my makerbot replicator, but when sliced and printed on the Prusa suffer from was you see below.

I had thoroughly gone through the print troubleshooting pictorial guide to start troubleshooting, but no single picture seems to fit the symptoms I am seeing exactly. Basic print settings I have always used in the past with no issues, that I am again currently using now are:

• 215°c Extruder Temp
• Filament Diameter 1.75mm
• Filament Multiplier 0.90 (also have tried 0.97, 0.99, and 1)
• 50°c Print Bed temp (1st layer)
• 0°c Print Bed temp (all other layers)
• Fan Speed 80 - 100%
• Perimeter speed 60mm/s
• Small perimeter speed 60%
• Infill Speed 60mm/s
• Solid infill speed 80%
• First layer speed 50%
• Top Solid Layers 4
• Bottom Solid Layers 4
• Infill density 25%
• Recilinear Infill

Does anybody see anything that stands out to them that could cause this? Are there any other good resources for troubleshooting? Any help in resolving this would be greatly appreciated.

Hi, welcome to the forum.

Did you just take the fan off the extruder to take the photos? If not, that's likely to be part of the problem. The large block of aluminum at the bottom of the extruder is the thermal sink that cools the steel heat-break, but it will likely need a heatsink and fan to be effective enough for pla. If you are printing without a fan then you have an advantage in that you'll be able to easily see what happens during the missing extrusion. The two options are that the motor stalls (the gear clicks back) or the motor keeps going and chews a segment out of the filament. A third possibility is that the motor stops dead, in which case the stepper driver has overheated and shutdown temporarily. If the motor stalls you may need more current (higher driver Vref) to get reliable extrusion. If it chews filament then you need more idler tension. If the driver overheats then the Vref is too high and/or you need active cooling for the electronics board.

Is your extruder calibrated?
Just asking as in the top infill it looks far too much, could be your settings though.
To me the cubes look like the extruder stopped extruding during the print.
Did you notice that the extruder clicked, jumped or made fancy noises in the problem area?
The plastic meant for this area needs to go somewhere if you don't have a big blob of plastic hanging somewhere on your hotend than I would state the filament was not transported.
Does the same happen at lower speeds too?
If in doubt print again and pay close attention when the problem starts.

Try lowering the themperature. I dont see a fan cooling the heatsink there, but could be on the side... Anyway, 215 degrees might be too much for your extruder, even if you have a cooler, the heatbreak at that temperature could be warm enough to make PLA soften and temporarly clog the heatbrak, causing extrusion to tstop.

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JamesK
Hi, welcome to the forum.

Did you just take the fan off the extruder to take the photos? If not, that's likely to be part of the problem. The large block of aluminum at the bottom of the extruder is the thermal sink that cools the steel heat-break, but it will likely need a heatsink and fan to be effective enough for pla. If you are printing without a fan then you have an advantage in that you'll be able to easily see what happens during the missing extrusion. The two options are that the motor stalls (the gear clicks back) or the motor keeps going and chews a segment out of the filament. A third possibility is that the motor stops dead, in which case the stepper driver has overheated and shutdown temporarily. If the motor stalls you may need more current (higher driver Vref) to get reliable extrusion. If it chews filament then you need more idler tension. If the driver overheats then the Vref is too high and/or you need active cooling for the electronics board.

Thanks! The extruder fan was removed to take the photo, I typically have it running at 80 - 100% speed. The motor does appear to stop at times. I am thinking of thermocoupling the motor and measuring the temperature to understand if it is overheating. I was thinking it was due to a clog somewhere in the hotend.

Quote
Downunder35m
Is your extruder calibrated?
Just asking as in the top infill it looks far too much, could be your settings though.
To me the cubes look like the extruder stopped extruding during the print.
Did you notice that the extruder clicked, jumped or made fancy noises in the problem area?
The plastic meant for this area needs to go somewhere if you don't have a big blob of plastic hanging somewhere on your hotend than I would state the filament was not transported.
Does the same happen at lower speeds too?
If in doubt print again and pay close attention when the problem starts.

I have only calibrated the print bed, not the extruder (flow rate I am assuming you are referring). I will have to look this up and calibrate this. Thank you for the suggestion.

The extruder does in fact stop extruding during certain points. No jumping occurred. Sometimes it extrudes normally, sometimes lightly, sometimes not at all, and sometimes heavily. This appears to occur at all speeds and on all layers. I have heard the servo click or hesitate, which seems to coincide with the extruder not extruding at all, suggesting a clog to me. I've cleared the nozzle and even replaced it, but this hasn't helped. Something more is causing this I would think. If I gently hold the filament and manually extrude, it does feel that it extrude stops extruding at times, as if the servo were stalling. I have checked to make sure the gear depicted above aligns with the hole on the top of the hot end, and that the set screw is tightened sufficiently. I am incline to think that I'm experiencing a reoccurring jam or clog. But what cause the root cause be? (If, in fact, that is what what I am experiencing)

Quote
Tinchus
Try lowering the themperature. I dont see a fan cooling the heatsink there, but could be on the side... Anyway, 215 degrees might be too much for your extruder, even if you have a cooler, the heatbreak at that temperature could be warm enough to make PLA soften and temporarly clog the heatbrak, causing extrusion to tstop.

I do in fact have a cooling fan that was removed for the photo, you can see the wiring tucked off to the side in picture three. I have tried printing at 205°c, 210°c, and 215°c, all with the same result. I can try lower, but all my other printers operate at around 215c, I would think this shouldn't be a problem.

Ok one of the first things I do when everything else seems to be fine is using a different filament, sometimes you just got a bad spool...
Another trick up my sleeve is the manual friction test:
Take the hotend off and extrude about 20cm of filament with quite some pressure on the wheel and while giving it resistance with your fingers - you want to really feel the filament being firced out between your fingers.
Clean the hotend out and remove the nozzle, you might have to heat it up first!
Now take the sample filament you created and push it manually through the hotend - leave the bowden connector attached (if you have a cm of tube to spare put a short lenght in there.
Turn it in all directions, move it up and down and try to feel spots where the damaged filament might get caught.
Usual suspects are the area where the bowden connector is and where the coldend joins the heat break.
If you feel resistance or even moments where you struggle to push it through use some fine sandpaper on a stiff wire to remove the edges.
In many cases the heatbreak has a short end for the heater block and a long end for the coldend, seperated by a thinned down section with no thread.
At the longer end the thread at the start should be removed to allow the top of the heatbreak to form a gapless seal with the hole of the coldend.
Last but not least is the actual heating chamber.
Heatbreak and chamber hole should not match!
You want the diameter of the hole in the nozzle to be slightly less than the hole in the heatbreak.
The heatbreak itself should be a really snug fit for the filament with little to no room to play.
If you feel a lot of resistance pushin the testfilament through try just the heatbreak itself.
In many cases it is not fully polished and has a rough inner surface.
Half an hour with fine sandpaper on a cordless drill will fix that - be aware that you have to clean/replace the sandpaper often as the stainless steel wears it out quick and fills it up too.
Once smooth use the last sandpaper roll and add some metal polish to get a shiny finnish.
The difference between a heatbreak that was just drilled out and a polished one is like driving your car with the handbreak on