Hey gang, Tim here at Core Electronics and today we're increasing our knowledge of 3D printers by exploring purge towers and ooze shields.

Dual extrusion printing is an absolute treat and polyvinyl alcohol as a support structure is truly worth a celebration. 

You can produce immensely detailed models with a ton of supports and not be concerned about removal. Just immerse your model in water and watch all your post-processing fears dissolve along with the supports. It's a sweet feeling indeed. And this is not even bringing in the fact that you can create a 3D printed model with various colours and multiple different material properties.

But to do dual extrusion print successfully like this, the use of both purge towers and ooze shields are immensely valuable. 

So to re-establish, dual extrusion printing is the process of 3D printing with multiple filaments, in a single print. When it first arrived, it ushered in huge vast new potentials. You can now print composite materials, produce with ease multicoloured components and have drastically advanced support structure options. All at your fingertips.

So when 3D printing with two separate materials, a purge tower or an ooze shield is required to prime the nozzle for the next layer. These techniques are an added complexity and expend filament, but their use guarantees an enhanced overall print quality. Furthermore, using both gives the best opportunity for your 3D print to succeed.

So without either a purge tower or an ooze shield, you'll end up with stringy hair-like filaments covering your desired component and have blemishes all over the surface. This happens when the filament being printed is swapped to the other filament. 

When this happens, the 3D printer will perform a retraction on the no longer used filament. Retraction is when the filament is wound backwards away from the extruder's head. This is done to reduce the pressure inside the nozzle so that the filament does not continue to come out of the nozzle tip. 

However, there is still pressure inside the nozzle. Perfection has not been reached in this regard and it is common for material to continue to leak out the very tip of the nozzle. So these leaks end up as those stringy filaments on your model. These can cause errors in your print, requiring post-processing and possibly fail the 3D print entirely.

Purge towers and ooze shields are available as options inside Ultimaker Cura and require only a couple of user-inputted parameters to give the best results. Put simply, Ultimaker Cura is a software which allows you to turn the computer file of your design into a recipe which a 3D printer can follow. It is available online and is a completely free software used by over a million users worldwide.

So you may be wondering why this ooze shield looks so peculiar. It's because this ooze shield used to cover this model. And you know that stringy filament that I was talking to you about? That's what you can see all the way around the ooze shield. By using this ooze shield in combination with this prime tower, I was able to print this model without any of those blemishes showing up on the actual surface of the piece.

Some of these settings talked about will be hidden settings in Cura. To be able to make them visible in the print settings menu, go to the top toolbar, go into settings, go into configure setting visibility, and then type in the name of the particular setting you'd like to see. By clicking on this, you'll now be able to see these settings over here in the custom print setting menus.

So let's start with purge towers. 

Purge towers are an additional print created on the build plate made to the height of the component desired. It is a hollow cylindrical object with a layer of the first material and then another layer of the other material forming a ring around it.

 As you can see in here, the outside is black tough PLA and the inside is PVA material. Whenever a nozzle is swapped between, the purge tower is built slightly higher. There is a layer which does not need a nozzle swap. The purge tower is the last section to be printed on that particular layer. 

To ensure the prime tower is sturdy and capable of holding all the oozed material, the nozzle purges a small volume inside the tower. The tower acts as a waste bin and collects all the excessive material. This is utilized also in the printing operation as a method to clean excess material off the nozzle as there is a surface for them to rub against. This cleans the nozzle before continuing the printing process.

So let's take a dive into all the settings Ultimaker Cura offers to adjust purge towers. 

Prime towers and purge towers are interchangeable words, so we're looking in the settings visibility menu, just because this shows all the settings together. 

So starting with enable prime tower, by clicking this checkbox, you enable the use for prime tower. Prime tower size underneath, this decides the width in the XY direction of the cylindrical prime tower. A larger footprint will create a more stable prime tower. The prime tower minimum volume down here, this decides the volume of the prime tower. The volume must be enough for the nozzle to be able to prime properly against it. Prime tower flow, which is up here. This is the overall nozzle flow of the prime tower and this is set to 100% by default. 

The prime tower brim, which is down here, and definitely click this checkbox because it creates a brim base to the prime tower. Using this creates much more stability on your prime tower. 

You also have the prime tower XY position and this positions the prime tower as seen from the origin point in Ultimaker Cura and a good location is near the switching bay between one nozzle and the other as this will lower the printing time. 

The prime tower will be made to the same size as your model. If your model is tall, the prime tower will also be tall. So in this scenario, it is liable to be toppled over by the print nozzle as it's wiping itself. Also certain materials when cooled are inclined to curl upwards. If this is not correctly accounted for in the software, it will cause the print nozzle to hurdle into the top edge of the purge tower and batter it down. Once the purge tower has fallen, stringing and negative effects on the model will be able to occur. Furthermore, there is a possibility that the print can be held up or failed as the purge tower could roll into the model being printed.

So my recommendations to get the best out of your prime tower has to do with increasing its stability. 

Start by increasing the prime tower size from the default 20mm to 35mm. Next always ensure the prime tower brim setting is activated as all the stability and grip of the tower, to the build platform comes from these two settings. Increasing these values will give dramatically more grip to the build platform for the prime tower.

Now ooze shields are a one layer wide wall that encases but does not touch the final model. This thin wall is made by altering materials layer by layer. It catches the ooze from incoming nozzles before each layer is printed. Thus the ooze shield is the first section printed for each and every layer. This acts as a barrier against the unwanted leaking material ending up on your final 3D printed model. The effective use of an ooze shield will save a lot of post processing.

So jumping into the computer you can now see over here in the print setting custom menu, all the options available for ooze shields. Starting off we have a checkbox to enable ooze shields. By clicking this an ooze shield will be made over your model. The next thing we have is the ooze shield angle. This is the maximum angle the ooze shield can have, and this is done to prevent the shield from collapsing. A smaller angle will lead to more material being required.

Next, we have the ooze shield distance, and this determines the distance between the ooze shield and the model in the XY plane. This is used to prevent the ooze shield from merging undesirably with the model. The ooze shield is a separately printed one layer wide wall which catches ooze from incoming nozzles before each layer is printed.

So, keeping that in mind, adjusting the ooze shield distance to be a distance of around 2mm away from the model and an ooze shield angle of about 60-degrees will work well for most materials and 3D printing situations.

I hope this has been valuable and inspired future 3D prints. Until next time, stay cosy.