A little help with misprints

[aaron 2]

Okay, I understand 3d printing quite well and have been in the hobby for a considerable amount of time. However, I can't figure out why this is happening. On some of my larger prints there is a layer in which the outer layer is not printed. I cannot figure out why this is happening. I know it has nothing to do with the z axis or x and y axis friction issues. Any ideas? Any help is appreciated.

A picture can be found here:

http://umforum.ultimaker.com/index.php?/gallery/album/325-printing/

It is the last picture.

 

[jonnybischof 60]

You're referring to the green box with the "G", and there's only the two layers pretty far up. Right?

If that's so, then I can't think of any problem related to printing (which doesn't mean much :-P ) because then the problem should occur more often...

Maybe there's a problem with the SD card, like larger prints = larger files, and maybe there's a damaged sector on the SD card. Maybe do an error-check on the SD card?

Have you looked at the Layer preview in Cura (if you're using Cura..)? You should be able to see whether there is a line planned to be there or not...

/edit: Oh, one thing: It could be a feeding problem if your extruder is pulling on the filament but the spool doesn't move on the holder until the force is high enough, making the spool "pop" and unwind a little. Then the tension starts building up again until the static friction is overcome again -> "pop"...

It could be that you get some underextrusion every time before the spool pops.

This should be easy to observe. I've got that phenomenon with the "popping" spool all the time, but until now I've not been able to make a definitive connection to sporadic underextrusion.

I guess my case is more related to uneven diameters of the filament, but that shouldn't lead to completely empty lines...

 

[msurunner 2]

/edit: Oh, one thing: It could be a feeding problem if your extruder is pulling on the filament but the spool doesn't move on the holder until the force is high enough, making the spool "pop" and unwind a little. Then the tension starts building up again until the static friction is overcome again -> "pop"...

It could be that you get some underextrusion every time before the spool pops.

This should be easy to observe. I've got that phenomenon with the "popping" spool all the time, but until now I've not been able to make a definitive connection to sporadic underextrusion.

I guess my case is more related to uneven diameters of the filament, but that shouldn't lead to completely empty lines...

 

That would be my guess. I see that from time to time on my prints. Usually seems to be a by product of either being slightly off on filament settings (either too cold or slightly over extruding, generating pressure on the extruder eventually) or too tight of a coil on the filament generating too much friction in the bowden. Try cleaning the drive bolt and check to make sure there aren't any straggler dust/grind particles or filament threads in the bowden tube and bump the temp up a bit if you notice it mid-print.

 

[aaron 2]

Thanks for the feedback. I think you guys may be right if it were not for the fact that the error occurred exactly at the outer edges of the print. There was a perfect and definitive absence of material there. If underextrusion or friction were the case, I believe it would be more erratic and random. So do I have a slicing error?

 

[jonnybischof 60]

Did it occur only on the outer edges? Because if you didn't watch the print it may well be that there are more errors but inside the print where they are not visible...

And the possibility of SD card filesystem errors remains. Did you check that?

 

[gr5 2,181]

This is definitely under extrusion and it is probably on the inner layer as well. I like the many theories above. The most likely is the spool got stuck or tangled. But you may have gotten a partial clog due to dust or you many have been printing too fast/cold.

What was your printing temperature, layer height and speed? (that's all I need to know).

It could also be a slicer issue but this is less likely.

 

[aaron 2]

Well, I believe I was printing at 240C, 80 mm/s, and .24 mm layers.

As for the SD card, I use a USB setup. I have two computers so this isn't an issue.

Next time I print, I will keep a closer eye on the printing process and the spool and see if I can identify the issue.

 

[gr5 2,181]

Those parameters seem okay. Pushing it a bit but it should be fine. I still like the tangling hypothesis. Or temporary clogs. Is this a dusty environment? Someone recently found that the clip that holds the bowden down on the extruder (which has blades in it) was shaving tiny pieces of clear bowden tube and they were getting transported along with the PLA and causing nozzle clogs. But your problem only seems to last a layer or two.

I would certainly go to .2mm layers *or* 50mm/sec (not both) which will put less strain on the feeder. Just to see if it helps. But normally 240C, 80mm/sec, .24mm layers should be okay.

[aaron 2]

Thanks for the feedback. I will certainly try it and post my results.