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What's going here? Lack of retraction? Skipping Bed? Missed layers?

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I have been having a sporadic problem with occasional prints where it seems to lower the bed too much (I have seen the bed drop and then the print has to play catch up on the next layer resulting in the poor layer.

I have checked the files both in Cura and Mesh lab, including checking the x-ray views and layer views and nothing seems to be amiss (I also have all boxes in Fix horrible turned off) but the problem still crops up from time to time.

The string of material between parts also suggests that the PLA isnt retracting fully on that layer. It tends to happen more when printing a singular small item hence printing multiple items at the same time.

I have also noticed that occasionally the material that is being fed will get chewed up by the knurled part of the stepper motor that feeds to the bowden tube. Would this cause the issues shown?

Any advice or pointers given would be greatly appreciated





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Apart from the issue in the first phrase, which appear to be related to a Z axis issue, there is lots of under-extrusion. You also mentioned the knurled piece chewing the filament. Until guys more experienced with UM2 will come up, here are some "generic" potential causes:

- extruder idler pressure to high (there is an adjustment screw and a white pointer on the extruder black case on the back side of the printer)

- temperature to low foor the speed and material you're using, making hard for the extruder to push the filament through the nozzle

- start of a clog in the nozzle

- deformation of the teflon piece on the cold side of the hotend

You do not mention any "clicking" noise, but you have not notice it. If it is present, it indicates the extruder motor is skipping steps, which is a feature aimed to preventing filament from being chewed. Otherwise, it means the current setting for the extruder motor is too high.

Basically, you have to track all the way up and down that the filament is carried. Somewhere and for some reason it has a hard time to advance :)


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Thanks for the comment 3dmaker. There is an occasional click and I notice that when feeding the material it is quite badly imprinted with the knurl pattern from the feeder.

I will try with adjusting the feeder motor first.

What is frustrating is that it has seemed to get progressively worse and can crop up at a moments notice. Most annoying 85% of the way through a 6 hour print of a pistol grip which continued to print perfectly after the skipped layers before doing it again just before the end...



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Are you saying the rod can stick out the side of the printer? This is very easy to fix. It is held in place with a combination of black plastic spacers and the pulleys. One of the pulleys slipped so it must not be tight enough also.

Now to your underextruded layers. It could certainly be a Z axis issue - on the gun grip it sure looks like the Z axis moved too much. Having underextruded layers however looks almost the same but that is a BIG skip there.

What temperature, layer height and speed did you print at?

Consider putting the filament on the floor - it can rub severely on the feeder unless you have the new feeder with the metal gromet. Even then it should work better with the filament on the floor.

You may need to grease the z screw or oil the two Z rods. Consider sliding the bed up and down by hand with power off. See if there are sticky spots.

There is a white teflon isolator that you can see if you look at the print head. The bottom of it touches the hot end. This part can get gradually worse over months of printing. You can often fix it by simply drilling it out with a 3mm drill. Or you can order (well you can get a free one from support I imagine) a new one if it is deformed enough that it is difficult to push a small piece of PLA through it.

You are going to have to figure out if your problem is Z axis related or underextrusion related. Again what is your temp, layer height and printing speed?


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Hi GR5, The axis rod fix was simple enough. It seems as though the grub screw despite being tight wasn't tight enough and the pulley along with the spacer move inboard which allowed the slop.


I did run another print after fixing an unrelated buildplate temp issue (loose wire due to poor quality clamp at the control board end) but the issue cropped again.


I have since cleaned out the material feeder in an attempt to eliminate that as an issue

Print settings are as follows...

Temperature: 210c

Print Speed: 50mm/s

Layer height: 0.1mm

Please note I am still very much getting to grips with 3d printing so my settings if seemingly odd are simply because that was preset or through experimenting

I am not sure what metal grommet you mean regarding the feeder but I have taken your advice and placed the reel on the floor. I have spotted plans for an alternative feed system that I will look into. The z screw and both rods have been greased up and there is no hitching or difficulty during travel when moving the bed by hand.

Many thanks for your help


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Fun Update time.

So After playing around with the settings I tried another print. Slightly different issue this time where the head move from one side of the part to the other whilst still extruding....


You can also see in the first few layers of the print (after the brim) the head has crossed the part again but as it was close to the bed treated it as a normal path...

The settings this time were...

Temperature: 230c

Print Speed: 25mm/s

Layer height: 0.1mm

Shell Thickness 1.6

Bed Temp 60c

I hope this additional info may help in diagnosing the problem as that is 3 prints in a row that have to be scrapped :/


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Looking at the pistol grip pic with two areas of under extrusion followed by normal extrusion, I did wonder if the filament is sticking in the Bowden tube. It might be worth watching the print and when the under extrusion starts then stop the print and measure the width of the filament from just before the start of the drive mechanism all the way through to the extruder.


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You have a slipping X axis. Most likely the pulley on the X motor. Very easy to fix - you might have to remove the cover to get at that screw but most likely not. Whoever put your printer together seems to have left a few screws too loose. To clarify these are the "set" screws or "grub" screws embedded in each pulley. There are 6 pulleys on the X axis - you should tighten all 6 but the most likely pulleys are the 2 on the short belt and of those 2 the most likely one is the one on the motor. This guide talks about it:




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Or maybe it's your Y axis if you moved the print - I see you moved at least one of them.

I still think you still have some Z axis issue also. Install pronterface and move the Z up and down in small steps and see if it sticks or move the bed up and down with power off with your hands to see if there is a sticky spot.

printrun/pronterface/prontrface download:




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