What Causes Missing Lines in 3D Prints? (How to Fix?)

While there are many different ways for a 3D printing process to go wrong, the most noticeable scenarios are, without a doubt, the ones where the models end up having imperfections on the surface that affect their aesthetic qualities.

Unfortunately, such issues are also as common as they are noticeable due to under-extrusion and over-extrusion being the primary causes behind them, which are problems that can be due to a large number of either hardware or software-related factors.

Today, we will be focusing on the issue of the appearance of missing lines on 3D printed models, where some of the print lines on the model end up having gaps instead of being filled with plastic, making the model look incomplete.

So, what causes missing lines in 3D prints?

Missing lines in 3D prints can be the result of a few different problems that cause under-extrusion, which we have listed below:

  • The nozzle of the 3D printer is clogged.
  • The nozzle temperature is way too low.
  • The print speed is way too fast.
  • Retraction is too much due to incorrect retraction settings.
  • There are issues regarding the extruder assembly.
  • The nozzle is too close to the build surface (first layer).

Moving forward, we will examine the reasons behind missing lines in 3D prints in more detail, find out what we can do to fix the missing lines issues as efficiently as possible, and go through the signs that indicate you may be facing this problem.

What Causes Missing Lines in 3D Prints?

While under-extrusion is clearly the problem that causes the missing lines to appear on your 3D prints, the fact that there are many distinct factors that can cause under-extrusion makes identifying this problem a challenging process.

Below, we have listed the most common culprits behind the issue of missing lines in 3D prints alongside a detailed explanation for each:

  • Clogged 3D printer nozzle – A partially clogged nozzle can render the 3D printer unable to extrude plastic on some regions of the model, which can cause the problem of your 3D printed model missing lines.
  • Low nozzle temperature – A low nozzle temperature can prevent the plastic from flowing freely at times, creating missing lines on the model due to the plastic not being able to get out of the nozzle.
  • Too high print speed – A too high print speed can cause the extruder not to be able to keep up with the required amount of filament to print all the layers successfully, causing the 3D printer to go through some regions of the print without extruding any plastic.
  • Too much retraction – Too much retraction can mean that the 3D printer is pulling the filament too far or that it’s not priming it quickly enough after retracting, with both cases leading to missing lines due to the absence of filament on the nozzle.
  • Problems with the extruder – Problems with the extruder stepper motor, loose extruder gears, low extruder tension, and issues with anything else that plays a role in the movement of the filament can cause missing lines.
  • Nozzle too close to build surface – When the nozzle is too close to the build surface due to problems such as a bed that is not level or a misconfigured Z offset, the plastic won’t have enough space to come out of the nozzle, which can contribute to the missing lines on the first layer.

While this list isn’t completely exhaustive due to the possibility of under-extrusion occurring as a result of more complex factors, such cases are pretty rare compared to the common culprits we have listed above.

How to Fix the Issue of Missing Lines in 3D Prints?

While there is no targeted solution to the issue of missing lines due to the many culprits that can be behind the problem, going through a checklist that covers all the possibilities is an efficient way to resolve the issue as quickly as possible.

Below, we have a list of solutions for the most common culprits that can cause the issue of missing lines in 3D prints:

  • Unclog the nozzle – Performing a cold pull or completely disassembling the nozzle are both suitable methods to unclog a nozzle that has been partially clogged. We would recommend starting with a cold pull as it’s easier to perform and only disassemble the nozzle if cold pull doesn’t get the job done. 
  • Increase the print temperature – Increasing the print temperature towards the upper end of the recommended temperature range for the filament you use in 5-degree increments can be helpful to allow the plastic to flow more freely and eliminate under-extrusion.
  • Lower the print speed – Lowering the print speed will give the 3D printer enough time to extrude sufficient amounts of plastic to complete the layers. We recommend going down in 5-10 mm/s increments and running a series of test prints to observe how the change impacts the prints.
  • Decrease the retraction – Both decreasing the retraction distance and increasing the retraction prime speed should be helpful, as these two parameters are the ones that can cause problems on the retraction front.
  • Maintain the extruder assembly – Increasing the extruder tension, tightening (or replacing if they are worn-out) the extruder gears, and looking out for signs that may indicate the extruder stepper motor has problems (such as clicking sounds) are the primary things to do.
  • Increase the space between the nozzle and the surface – After ensuring that the bed is leveled correctly, the distance between the build plate and the nozzle should equal the thickness of a paper while the printhead is homed at the Z-axis, which you should configure through the Z offset parameter.

We highly recommend running a test print with the model you’ve been facing the issue of missing lines with after applying each solution to find out whether the fix was successful or not, which will be helpful to pinpoint the problem and avoid it later on.

How to Identify the Issue of Missing Lines in 3D Prints?

Identifying the issue of missing lines on your 3D printed model as early as possible, without committing more material to different prints that will suffer from the same problem, is one of the best things you can do to resolve the issue as quickly as possible.

The most apparent characteristic of a 3D print that is missing lines is the appearance of gaps where layer lines should be, essentially creating a look where the 3D printed model contains some narrow spaces that horizontally span a specific (or sometimes the entire) area of the model.

Since the problem of 3D prints missing lines is a result of under-extrusion, we can say that these spaces are the parts of the 3D printed model that the printer has failed to fill with plastic and are weak points that can cause the 3D printed model to be more prone to physical damage as well.

Wrapping Up

The appearance of missing lines on a model can definitely be disappointing, especially if you have printed a large and intricate object and haven’t noticed the problem until the printing process was complete.

To recap, factors that cause under-extrusion, such as a low nozzle temperature, too high print speed, too much retraction, the nozzle being too close to the build surface, a clogged nozzle, and issues with the extruder assembly can all cause the problem of your 3D prints missing lines.

Aside from problems with the extruder assembly, which may require a more technical process to solve, the issues we have listed above shouldn’t take too much of your time to go through and apply the appropriate solution when necessary, and get your 3D printer back in working condition in no time.

Happy printing!