How to print PLA right

As many of you already know, PLA is one of the most popular materials in 3D printing due to multiple reasons: it’s easy to print, it’s affordable, it’s a bioplastic… As a result of all these reasons and more, PLA turns out to be very convenient for makers. Here, we’re going to tell you how we print PLA right using Cura.

In this post we don’t intend to explain you all the properties of PLA. Our purpose is to share our experience printing with it and tell you how we achieved impressive results with no stringing, gaps or seams without spending a lifetime waiting for the printer to finished, just because you thought that if you print very slow, you will get amazing results. In fact, that might be true, but it’s also true that you might become a skeleton before it finishes.

For those who just have started in the 3D printing world, I’m sure you will find this post useful. I would also warn you that we are going to use advanced settings, but I will explain all of them step by step so don’t worry.

On the other hand, if you are an expert already, you are also invited to stay and read it. We would love to share opinions a learn from you!

So, after this short introduction, let’s get started and see how to print PLA properly!

What are we using to print PLA?

First of all, we should explain what material are we going to use. Our printer is an Ender 3 from Creality with a nozzle of 0.4mm diameter. Quite standard, isn’t it?

Another essential part is the slicer. We use Cura: it’s intuitive, powerful and free. The settings described below are tested in Cura, but any other slicer will have similar options so you can look for them.

Regarding the filament, we try to use local manufacturers. There are plenty of good products closer than you think. It really worths taking a look! Test some of them and pick the one that you like the most.

Basic settings to print PLA

First, we’re going to start with the basic settings. I mean all those settings that are already visible in Cura in a basic configuration, so we can have a start point to print PLA right.

Quality

We often use 0.2mm of layer height as the standard. For better resolution we might decrease to 0.16mm. On the other side, for rough printings, 0.28mm gives good results too.

Remember that you must never exceed a layer height over an 80% of your nozzle’s diameter. In this case, our maximum layer height would be 0.32mm. This is important, since bigger diameters would seriously jeopardize the adhesion, resulting into low printing quality.

If you want, you can also increase a little bit the first layer height to foster adhesion.

Shell

Here we can determine the walls width. The parameter Wall thickness will set the width of the walls in millimetres, while the Wall line count sets the number of wall, independently of the thickness. Both are codependent, so if you set one of them, Cura will adjust the other one automatically.

With 2 or 3 perimeters is enough. Less than that could make the part brittle and more will increase the printing time a bit too much, although it will be more stiffer.

On the other side, leave at least 3 top and bottom layers (0.6mm in our case). Less than that will make the base and the top face quite brittle.

We will be back to this block to look for more advanced parameters, but everything at the right time.

Infill

Here we have two essential parameters: the Infill density and the Infill pattern. Both affect directly to the stiffness of the object.

The infill density determines how much material you put in the inside of the object. A 100% would mean a completely solid object, while the 0% is a hollow print.

For decorative figures that don’t require too much strength, a 10% infill is OK. If you need more resistance, try between a 20 and a 30%. More that that wouldn’t give a significant increase in stiffness. However, there might be cases in which you prefer a completely solid object. After all, each situation requires analysis!

Regarding the infill pattern, Cubic and Gyroid work well with any kind of print. The actually give a good deal in stiffness for those prints that have higher mechanical requirements. Patterns like Concentric or Cross can enhance flexibility, whereas Lines and ZigZag can make the object brittle. The later might be good for supports, so they can be removed easily.

Material

Now, we get to the core. This block determines the printing temperatures, probably the most important parameters in 3D printing. Why? Because if we don’t set them properly, we wont’ print, neither wrong nor right. Well, maybe wrong. Let’s see how to set them to print PLA right.

We have to differ between two temperatures: the Printing temperature and the Build plate temperature.

The printing temperature refers to the temperature in the nozzle, which means that the material is going to be fused and placed at this temperature. We need the necessary temperature to ensure that the filament is melted and it sticks to the base.

A common range of printing temperatures for PLA is between 200°C and 220°C. There are some brands that allow you to print up to 230°C. In any case, pay attention to the recommended range given by the manufacturer. They know better that anyone how the material is going to behave. We usually print PLA with 210°C and works very well.

In general, a higher temperature enhances adhesion between layers, but can also produce more stringing. However, the later shouldn’t be a problem if we configure all the parameters right. We’ll see how later.

About the temperature towers

In addition, you can print a temperature tower. There are many in Thingiverse or any other repository. These are towers whose floors are printed at different temperatures so you can see better the results of each one. We will right a post on how to do it as soon as we can, but for now search in Youtube. There are many good guys who explain how to configure Cura to do this. It’s quite easy.

Regarding the build plate, we always set some temperature for PLA. Between 40°C to 50°C is a good range. Although some people doesn’t use temperature in the build plate for PLA, we prefer to keep it a bit hot because it promotes adhesion. This is especially important if you have a narrow object with low surface contact between the part and the plate. It could take off quite easily! In any case, the filament manufacturer will provide you with some guidance.

Speed

It is easy to understand that the faster you do something, the less accuracy you have and the quality is affected. For instance, if we draw a dog, it’s not the same if we’re given 1 minute to do it than if we have 10 (despite our lack of drawing skills…). The same happens when you’re printing. However, you must bear in mind that if you print too slowly, the printing time will dramatically increase, so you might turn your print into some sort of a Sagrada Familia remake. I just hope you mind the tram, please!

So, we must find balance. A good Printing speed for us has always been 50 or 60mm/s. This works well to print PLA right. More than that won’t work well in an Ender 3 since it’s not that powerful.

Regarding the Travel Speed (Speed of the nozzle while is not printing), we like to leave it at 120mm/s so we don’t have to force too much the motors and reduce the inertia of the displacements, avoiding irregularities. It is also good to keep it high, since it helps to reduce stringing.

Sometimes, you might need more detail, so it might be suitable to lower down the speed. Sometimes is OK, don’t worry.

Travel

The next step is to set retraction. These settings are of upmost importance, since they mean a big deal in the appearance of the printed object and the amount of post-process.

Here, we’re going to adjust, in a gross way, these settings so we can remove most of the stringing problems. For those who don’t know yet, we refer as stringing the threads that might appear from one part of the printed object to the other side, specially when it has separated parts such as columns. This is caused because, when a layer is done and the nozzle moves to another point to keep on printing, the filament is still extruded by inertia, so the nozzle leaves a string of filament while it is travelling.

To solve this, we adjust Retraction distance and Retraction speed. The former is the distance that the extruder drags the filament back, preventing the stringing and the later refers to the speed with the extruder performs this operation.

The standard values that have been working nice for us are: 6.5mm of retraction distance and 45mm/s of retraction speed. Those are quite standard. You can always try to adjust them, increasing or decreasing distance in intervals of ±1mm, and the speed in ±5mm/s intervals.

Keep in mind that a high retraction distance can cause jams and too low will be useless. Besides, the speed must also be adequate: too low and the extruder won’t have enough time to perform the retraction; too much and it will have to pull too much the filament back, which can cause damage on it.

For now, we’re done with the retraction setting, but we will come back to this section later for more advanced settings.

Cooling

ENABLED. 100% fan speed to print PLA right. This refers to the speed of the layer fan. It points directly to the nozzle outlet, so it cools down the material as soon as it leaves the nozzle. This turns the melted filament into solid immediately, places it properly and helps to avoid stringing.

Supports

OK, just some advice about support. First of all, parts that form an angle ≤ 45° with respect to the build plate, will require supports. That’s the limit we have. Sometimes, it is possible to do bridges in parts that are close to each other, but for cantilevered parts don’t take the risk.

Regarding the Supports density, if it’s too high they will be too difficult to be removed. On the other hand, if they have a low density, the supports structure might not be sufficient to keep the filament, causing its collapse on the hollow areas of the supports structure.

We normally use around a 20% if the object is not too big. For huge sizes, you will need higher density.

Build plate adhesion

We always recommend to use a 2 or 3 layers skirt. It provides continuity to the plastic flow before i starts printing. Besides, by taking a glance to the skirt, you can easily see if the layers have adhesion or they’re not being placed properly (an unlevel bed won’t allow the filament to get stuck to the bed)

If you have a thin object with small contact surface with the plate, use a brim. Depending on the object, between 2 and 6mm can be enough. If you are printing screws, maybe 2 or 4mm is OK. For huge lithophanes, it might be 5, 6 or even more. Again, test it yourself. That’s the best way to achieve the results that better fit your printer.

We rarely use a raft. In some extreme cases it might be a good solution, but normally you can fix these adhesion problems with a good brim.

Advanced settings to print PLA

We’ve already gone through an overview of the general parameters. Now, we’re going to get serious to print PLA right. We will have to search for advanced parameters in the gear located at the right side of each block’s name. Just hover over it and the gear will appear. Then, click on it:

Access to Cura’s advanced settings.

For this section, I found very useful the articles I provide you at the end of this post. It worths taking a look!

Seams

In almost any piece of clothes, you can see seams where two pieces of fabric have to be sewn and joint together.

In 3D printing we have seams as well. They appear in the exterior wall, right where the nozzle finishes a layer and changes to the next one. There’s always some over-extrusion due to the inertia of the printer, so the excess of filament take the shape of an unaesthetic seam all over the surface of your object, from the bottom to the top of it. So, how can we solve or mitigate this?

There are a couple of parameters we can play with. First, go to the Shell block, click on the gear on the right side and look for the following parameters:

  • Outer wall wipe distance.
  • Z seam alignment.
  • After activating the previous one: Z seam X.
  • Also after that: Z seam Y.
  • Seam corner preference.

Once you have enabled them, let’s take a look to the meaning of each one.

Outer wall wipe distance

The Outer wall wipe distance is a small travel without extrusion to the infill area, right after the nozzle finishes the layer. Since there’s no extrusion, it results into a reduced seam, mitigating the over-extrusion at the end of the layer by hiding it towards the inner area. A recommended value is 0.4mm, but you can always test adding or subtracting ±0.1mm each time. However, don’t go too far from this limit, as you can cause under-extrusions that can turn into unfinished layers.

In this picture you can see those travels in blue, over the lower corner:

Outer wall wipe distance: small movements (blue) to the inner areas without extrusion. Retrieved from ultimaker.com.

Z seam alignment

The Z seam alignment allows you to control better where to place the seam in order to hide it. For instance, if you choose Sharpest corner, Cura will automatically start and finish a layer in a corner. The seam will be totally hidden at that corner and you won’t even notice.

Another option is to choose User specified (in Z seam alignment). Here is where Z seam X and Z seam Y come into play. These options allow you to choose the coordinates of a point in X and Y. Cura will finish each layer at the object’s external point which is closer to the one specified by you.

Seam corner preference

Finally, you can find Seam corner preference. This is used to tell Cura the influence of the object’s corners when it comes to hide seams. We normally use Hide seam so Cura understands that you prefer to place them in the inside corners. These will hide them much better.

We must note that in totally round objects it will be difficult (not to say impossible) to completly hide the seams. We can place it on the back area or maybe try to place it Randomly.

With all of this said, we’re done with seams. Now let’s see how we can make stringing disappear.

Stringing

This is a very annoying issue. Your print has already ended and you remove the part from the build plate. What do you see? A lot of threads and strings of filament going from one side to the opposite like little and disgusting thin worms. Of course, now you have to remove them.

Is there any way to get rid of those strings forever? With PLA, yes. We show you how.

The first thing you must do is to adjust retraction settings. It’s the big setting. We’ve already done that previously, so we’re moving to the advanced preferences.

The seam settings will also help to get rid of the stringing issue, so make sure you understand them.

Advanced travel settings

The next step is going to the Travel block. We go back there to enable the Combing mode. These settings keeps the nozzle within already printed areas, so if there is some excess of filament, it will remain inside the infill or the inner walls so the next layer will cover it. To do that, choose the Combing mode option “All”.

In the next picture, on your left side, you can see the combing mode disabled. The nozzle will move in a straight line to the next point. On the right, the combing mode forces the nozzle to move over the inner perimeter.

Normal travel mode (left) vs. combing mode enabled (right). Retrieved from ultimaker.com.

Obviously, the combing mode will make your printer to travel bigger distances, but the need for retraction is substantially reduced. Thus, it helps to remove stringing.

Experimental settings

Finally, we’re going to the Experimental block, click on the gear on the right side and search these two options:

  • Enable coasting.
  • Coasting volume.

Coasting is a very useful functionality to print PLA right, as well as other materials. It will replace the last part of the extrusion with just a travel move. With this, the overpressure inside the nozzle will release the last portion of filament during the coasting travel, at the end of the layer placement. Once this is done, there won’t be any remaining melted filament, so the nozzle travel won’t cause stringing.

Coasting. Retrieved from ultimaker.com.

Leave the coasting volume around 0.064mm3. It’s a standard value and it really works. You could try a cubic micron up or down, but watch out: this parameter is quite sensitive. Too much and it will results into under-extrusions.

Final advice

As you all know, nobody can tell you exactly how you must set your printer’s parameters and give you the panacea. The best you can do is to carry out your own tests.

However, it is true that some general tips like these turned to be very effective for us. When we print PLA, we rarely see a single string. We also know better how to hide seams and make printed objects with a very good surface finishing as it comes from the printer.

Speaking from our own experience, we think that you will find useful these tips. You can also take a look to the information provided by Ultimaker in their site. They have very detailed explanations of all the functions in Cura, so we do encourage you to check it out. We leave the sources at the end of the post.

For now, this is all folks. Keep practising and testing your designs in your printers. It’s the best way to learn and improve your techniques!

Remember that you can leave your comments here or share your opinions about how to print PLA right with us in our social networks or in our Contact section.

Sources

  1. Ultimaker support: experimental, travel and shell settings.

https://support.ultimaker.com/hc/en-us/articles/360012614559-Experimental-settings

https://support.ultimaker.com/hc/en-us/articles/360012611299-Travel-settings

https://support.ultimaker.com/hc/en-us/articles/360012512340-Shell-settings

  1. Kondo, H (2020). Cura Retraction Settings: How to Avoid Stringing.

https://all3dp.com/2/cura-retraction-settings-how-to-avoid-stringing/

  1. RepRap Calibration guide.

https://reprap.org/wiki/Calibration

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