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I have not been able to print smooth and round shapes using Cura 3.3.1 (or earlier) without bumps. I think they are seams? The filament is PLA.

Combing is enabled, which I thought makes it so that the nozzle travels over already printed areas, instead of flying over the air...right?

I have been able to keep the seems hidden for the most part when there are sharp corners. Sometimes cura hides the seems properly...sometimes it doesn't.

Here is an example shape I have tried printing with several different settings:

Cura printed object

The object above was printed using "random" seam corner preference. If I had chosen "sharpest corner", the bumps would all just stack up in one place, but still stick out.

Cura shape

Cura settings 1 Cura settings 2

Cura Settings 3 Cura settings 4

Just look at the travel lines below! Why is it jumping all over the place?

Cura travel lines

Cura travel lines single layer

I have tried "Avoid printed parts when traveling" enabled and disabled, doesn't seem to make much difference.

I feel that there should be a configuration that results in the nozzle not jumping through the air like that, but I can't find it. Perhaps that's not related to the bumps?

The printer is a MonoPrice Mini Delta.

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  • $\begingroup$ Do you print one part a time? $\endgroup$ – profesor79 May 15 '18 at 7:07
  • $\begingroup$ What is the nozzle temperature? $\endgroup$ – profesor79 May 15 '18 at 7:08
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    $\begingroup$ One part at a time. The temp is 195. $\endgroup$ – Bort May 15 '18 at 12:13
  • $\begingroup$ You may want to look in the coasting option, this option tunes the pressure in the nozzle chamber by reducing filament extrusion before the move, thus preventing those blobs. $\endgroup$ – 0scar May 16 '18 at 7:25
  • $\begingroup$ Possible duplicate of What do you call this effect in 3D printing and how can I remove it? $\endgroup$ – 0scar Jul 12 '18 at 14:28
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Following on from Toon's answer, here is a run down of Thomas Sanladerer's excellent video: 3D printing guides: Calibration and why you might be doing it wrong.

However, this may not be a definitive answer to the actual question about warts and bumps...


0:08 - A step back

Back in time - when the RepRap project (and the hobby grade 3D printing market) was new territory - it was seen to be a doable technology, with no restrictions imposed by patents. The new printers created and developed included Darwin, Sells Mendel and Prusa Mendel. These often produced unusable parts.

However, impromptu solutions, or kludges led to poor quality fixes giving poor quality prints, by today's standards. However, people (today) believe that because they worked back then,. that they must still be valid solutions today. However this is not necessarily the case.

The common misconception is that it is necessary to calibrate the esteps per mm for all axes other than extruder - adjusting the x, y and z esteps per mm until the 10 mm cube measures exactly 10x10x10 mm, even if that means squeezing the callipers.


1:25 - Car analogy

You find that your car pulls to the left, when going in a straight line, so you adjust the steering. However, then in hard corners and the rain the car handles poorly.

Upon closer inspection, it then turns out that the car had a flat tyre. You wouldn't compensate for having a flat tyre by adjusting the steering, now would you?


In order to get that 10 mm cube precise, it is usual to calibrate for the filament diameter, and extrusion multiplier (most straightforward option), but some printers aren't even that precise in the first place.

Mechanical, ripple, slaw, blacklash, can throw you off by 0.1 mm. Compensation for this 0.1 mm is certainly possible and achievable. However, then for a larger print, say 100 mm, then these overcompensation will become more evident, and you will be one entire milimeter off the desired dimensions.

So, use the ideal calculated esteps per mm. Timing belts and threaded rods are made to tight tolerances. therefore the worst case of ideal step per mm setting is an inaccuracy of 0.5%.

So, to find the ideal calculated steps use Prusa's calculator which is very good indeed.

If you are not using belts, or very large printer, then it is worth recalibrating the steps per mm for x and y, as 0.5% will make a noticeable difference in larger parts.

Use the files and instructions for these Calibration sticks on Youmagine, for proper recalibrating without results slewed by the extrusion multiplier being off by a bit.

3:45 - So what do I need to do?

What do you need to empirically calibrate your printer? In actual fact, not all that much:

  • extruder steps per mm setting
  • extrusion multiplier (see video link - Extruder calibration)

  • print speed, jerk and acceleration settings - These depend upon how much quality you want to sacrifice for increased speed.

    Pro-tip: slow your printing down. For example, try printing at half speed. Quality may be improved, and even if it isn't you will be able to observe more clearly what is happening, and going wrong. (see video link - Super Fast Guide:Tuning Speeds)

4:30 - Other than that?

There is not much else needs calibrating, per se.

With regards to slicer software, there are only a certain range of settings make sense, but this isn't printer calibration. You simply learn the slicer software and, with familiarity, see how far you can go.

These days any well maintained and well built and solid printer will produce good prints.

Most slicers give you decent prints without tweaking or calibrating, other than the basic settings about your printer and deciding how the part should be printed.

What about print temp and retract settings? Well, just use the default settings, or settings which depend upon the type of filament. So, no calibration is required there, as it is a property of the filament.

5:24 - Summing up

Don't try to calibrate everything

The technology, in particular the software, i.e. slicers, is still developing and improving. Slic3r's prototpye beta (in Nov 2014) has added compensation for fitting errors(?) without messing other things up, which is essentially what the cube calibration tries to do, but in the correct way.

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Have you correctly calibrated your steps per mm a.k.a. esteps? Tom made a great video about it:

3D printing guides: Calibration and why you might be doing it wrong

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  • $\begingroup$ Toon thanks for answering this open question that has gotten out of view. However, your answer is more or less a comment. If Tom's link dies there is not much to go on. I hope the OP tries your suggestion and reports back. In the mean time you can edit your answer to a more proper SE answer describing at least the basics of how to calibrate the extruder. $\endgroup$ – 0scar Jul 12 '18 at 18:19
  • $\begingroup$ Hi Toon, can you expand upon this answer? The best thing would be to take the main points made in the video, and note them in your post (if that is possible), or that if the link dies the information isn't lost. Else I will convert your post to a comment. $\endgroup$ – Greenonline Jul 13 '18 at 14:30
  • $\begingroup$ Following a written procedure is much, much more difficult to understand compared to watching the video. So i prefer not to write it out. There are already some great written instruction on the reprap wiki about about this subject. @Greenonline if it's more appropriate you can convert this post to a comment. $\endgroup$ – Toon Jul 16 '18 at 9:15
  • $\begingroup$ I understand completely. Some things just need to be watched rather than read :-) I will leave your answer as it is. $\endgroup$ – Greenonline Aug 6 '18 at 20:36

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