Bumps? How do I fix my prints?

[moejt87]

Sorry for the bad picture quality.

I’ve recently started getting these bumbs on my prints. Seems to be happening the most on non overhanging top surfaces.

I am using a lulzbot Taz 5

Print bed at 110C

Nozzle temp at 235C

50mms print speeds.

40C enclosure

IC3D filament

Am I extruding to cold? Seems to be slightly (only slightly) better when I put the nozzle temp up to 240C. Bad filament?

I Should also note that it seems to be worse on long passes. In other words, small parts being printed that only extrude a little bit here and there dont seem to be showing signs of this. However when I print something like the imperial star destroyer at 10" and the nozzle literally extrudes in a straight line for 10 inches… this issues shows up.

Thanks for any help.

[AardvarkMan]

It looks like over extrusion. Check the diameter of your filament, 3mm filament should measure about 2.85. There is a setting in your slicer to set the actual filament diameter. I’m guessing that your filament is actually a little wider on average so you are over extruding. You will need to check the diameter in several spaces.

Another option would be your retraction amount is too much, causing the extruder to sit in one place for a moment to retract the filament.

If it is one bump per Z Axis level, then check your retraction. If it is random, check your filament diameter.

Happy printing fellow Taz user.

[bogofoo]

Is there any chance the filament has been in a humid environment? It does tend to absorb water and that can cause snapping and popping (when steam bubbles out of the extruder). It could also cause these bumps during the extrusion. You likely wouldn’t notice in short print segments since the retraction pumps filament in and out and works out the bubbles. It does look like you’re over-extruding slightly (I see some bulges at the edge and corners) but that wouldn’t be a recent change like you mention. If you have a fresh pack of filament in the sealed bag, you could run a comparison print, or you can try drying it in a low oven (well below the glass temp for either PLA, ~60C or ABS ~80C), or some folks claim the refrigerator works too (it is quite dry).

[designreality]

Hi moejt87,

I would look at this guide even though is not for the lulzbot it has a lot of good info.

A visual Ultimaker troubleshooting guide - 3DVerkstan Knowledge Base

[Joshua_Napoli]

Has your filament absorbed moisture from the air? This can cause little bumps, when steam builds up and makes the extruder pressure irregular.

[moejt87]

It’s hard to be 100 percent certain but it does seem like it’s one bump per level. I have just been using the standard 1 mm retract at a speed of 10 mm/s with good results up untill now. I did slow down travel speed on a recent print and it made the bumps worse (i was hoping it might make them better) These bumps aren’t present on vertical walls. Is just when I do angled roofs/walls that they start to get bad. Maybe the oozing from the retracts just isn’t as visible on a vertical wall? I don’t get strings so I never assumed oozing as a problem. Although I do get marks on the top of my print. I tried upping the Z hop with little effect. So it must be oozing… Bad filament could always be a problem… I do normally hear popping noises on occasion, especially at the start of a print. However this latest print was a bag opened from factory sealed merely hours before. Had the same problems. There is always the option IC3D has crap filament. I went with them because they seemed to have the best reviews. I’m new enough that I haven’t tried anything else. Not sure about over extrusion. My measurements of the filament diameter are anywhere from 2.88 to 3.1 so I have tried to average them around 2.95… I guess I could try upping it to 3.0 diameter on cura.

[ericchou]

Thanks for sharing. That is an excellent visual guide!

[moejt87]

I have confirmed what the problem is. It looks like my nozzle is over extruding slightly when it starts a new line and when it ends the line. This is seen more on the round objects I try and print where it starts a perimeter then loops around and finishes the perimeter where it started, it then drags the nozzle inward to infill. When the nozzle goes in to infill it does not retract (why would it?) and yet more filament is deposited in that area.

I’ve tried playing around with my retract settings and it doesnt seem to make a difference.

I’ve lowered my extrusion and again it does not seem to help much. I’m clearly under extruding but it doesnt change the fact that a tiny bit of extra filament is deposited at the start and end of the line. It also doesnt help when the nozzle goes to infill, is there even a setting that would allow me to tell the printer to retract before moving inward to infill? I’m currently using cura.

Currently I’m printing a test print with only a shell (a thick one). The blobs are lining up in the same spot vertically because that is where each line begins and ends when there is no infill.

Any ideas or solutions? Maybe its time to switch to Slic3r?

[AardvarkMan]

In Cura there is a check box for “Perimeters before Infill”. This causes it to print the outside, then move inside to print the infill. You can clear the check box and it will do it in reverse order. It will print all the infill, then move to print the exterior before retracting and moving up a level.

You may want to give that a try.

[Schnaaab]

Hi,

I had the same issue with my Prusa i3 for a long time, a small bump on every level change. I’m running a Bowden type extruder so a lot of the issue was from the lack of rigidity of the filament between the extruder and hot end. Here are some of the steps I took to remove them, hopefully some may help:

-To double check it is the “z-scar” you are experiencing try switching to slic3r as there is an option to align Z moves, if all your bumps change to a continuous line up your part you know for sure that this is your issue.

-Lower hot end temp

-and slow outer profile speed

-Different filaments seem to be able to have very different flow and ooze characteristics.

-Increase retract distance and speed or use “filament pressure compensation” available in some slicers.

- try releasing the extruder and see if the filament jumps back by itself. your retraction distance will need to be at least this distance to make an effect.

-Some slicers have an “extra length on re-start” option a small negative value should help (I can’t remember if Cura has it)

-I know Slic3r also has a “wipe while retracting” function which starts the retraction before the end of the profile.

-Z-hop by the same distance as your layer height.

-Finally this is a real long shot, I have heard other makers saying that black filament tends to ooze more than others. (I think that it is probably more linked to manufacturer)

Hope some of that might help.

Cheers,

Rob

[boydconnor]

This is gold! Thanks for sharing, mate

[Jude]

You may also want to try a different brand of filament. It could be a quality of filament issue.

[williamlora0822]

but there is no troubleshooting for bumps

[BryanM]

Your problem sounds very similar to mine: bumps showing during circular cross sections only of print using black filament. Ive attached a cropped photo of the problem. It seems like it’s on nearly every layer, but never in the same spot. After some observation I think that a print head pause is the problem in my case as well, but I don’t know how to change that! Have you found a solution?

(I’m curious to try the same print in another color, because after hearing a Schnaab’s comment on the black filament I realized that I don’t remember seeing this problem outside of my black filament)

please let me know, Thanks!

Lulzbot TAZ5

Print temp: 240C

Print speed: 35-45mm/s

Material: Village Plastics ABS

[Gideon_Rossouw]

Any luck in solving your issue?