PVA not sticking to CPE raft + leveling issue

[B_Terneyre 0]

Hi

 

Our company has recently aquired an Ultimaker 3, and my colleague and I have been tasked to experiment with it.

 

We are new to 3D printing, so up to this point we have been experimenting with trial and error, tutorials and this forum to solve the various issues we have encountered. However, there are two problems for which we have not yet found a solution or a topic on this forum.

 

The first issue is with our CPE rafts: our parts require supports to be printed, so we have used the dual extrusion features of the Ultimaker 3 to print PVA supports. So far this has worked weel with our PLA and CPE parts printed with brims, but we wanted to experiment with rafts. However, while the CPE raft itself is always well printed, the first layer of PVA does not stick to the raft, resulting in the support not being printed and a PVA blob accumulates around the nozzle, messing up the entire print. We are unsure if the issue stems from the material combination of CPE/PVA (which would be strange, since the materials are supposed to be compatible, plus our PVA supports work very well with our CPE parts when we use brims) or from our printing parameters. Again, this would seem odd since for the most part, we have used default parameters of Cura, with two exceptions:

-We have lowered our CPE printing temperature from 240°C to 230°C, this has helped us solve our stringing issues, and is still within the recommended temperature range for CPE.

-We have increased our glass plate temperature from 70°C to 80°C. Again, this has helped us solve our plate adhesion and warping issues while remaining in the recommended range (We use DimaFix adhesive spray for the plate adhesion, which works better on higher temperatures). But the PVA is printed on the raft, so the higher bed temperature should not be an issue. Besides, our PVA supports come out well when we print with brims, where the support is in direct contact with the 80°C plate. 

Since we have run out of PLA, we are unsure if our problem is unique to a CPE/PVA combination on rafts, or if supports are not meant to be printed on rafts in the first place. We have had the exact same issue when we have tried to print a PVA raft: the first layer of CPE would not stick to it.

 

Our second problem is much less critical, but we have not found a solution either: each time we launch a print, a little bit of material extrudes from the nozzle during active leveling. Our parts still come out well, so it obviously does not affect the leveling process that much, but still leaves several bits of material hanging on the plate or sticking to the side of the nozzles. Is there any way to make sure the print cores heat after each active levelling?

 

Thank you for any help you may provide.

[tinkergnome 926]

 

First of all - using a raft on Ultimaker printers is very unusual - with the exception of very special use cases. I guess you'll get more complete answers if you elaborate a bit more the reasons why you are experimenting with rafts nowadays.

You don't mention which slicing software you use. Default settings usually produce a small gap between the last layer of raft and the actual model. That's probably the cause of the problem and this distance can be set to zero, if PVA is involved (but I'm just guessing - a picture of your model would be nice).
In Cura it's called "Raft Air Gap".

 

Active leveling on UM3 is nice if it works, but not mandatory. You can configure it to "never", ensure that the nozzles are clean and do a manual leveling from time to time. That's totally sufficient.

 

[B_Terneyre 0]

Thank you for your answers.

 

We are using Cura 4.3, which I believe is the latest version.

 

We wanted to use a raft to correct the warping issues we have had with some of our parts, since rafts supposedly give you a better adhesion than a brim. Why are rafts so unusual on Ultimaker as you say? Does the printing quality of  the UM3 make their use a bit of an overkill or is there a parameter we are missing?

 

We checked the default raft air gap on Cura and it is indeed higher than zero (although why is that the case? I understand the need for the raft to not be completely fused with the piece to take it off easily once the print is finished but how can the raft attach itself to the part if we essentially ask the printer to print in the air?). We will try to set it to zero on our next print. I unfortunately have no picture to show you yet since we dicarded our failed prints.

 

On a final note, we think we will continue using active levelling since it always seem to work well for us in spite of the hanging bits, although it would make more sense for the next version of Cura to heat the print cores after the active levelling to suppress this issue, if I may be so bold.

[geert_2 556]

Once you get your bonding method right, most of the time you can print directly on the glass, using that bonding method. No need for raft. This should also give a much smoother bottom side.

 

For special models, an option is to design custom brims or supports into the model in CAD, so they are part of the design. In this way you can enhance bonding where necessary, without affecting other parts.

 

For example in the model below, the cube (right) has a custom brim, to make sure it sticks well. Also the pink and orange supports have a custom brim, for more adhesion. Otherwise their ground contact area would be too small, and the nozzle banging into the overhangs would knock off these parts. Edges of overhangs tend to curl up, so they get a rough treatment from the fast moving nozzle slamming into these edges. This is a small model: the watermark text is 3.5mm caps height, and its legs are 0.5mm wide.

 

 

[B_Terneyre 0]

Thanks for the tip, but how do I integrate the custom supports/brims in Cura? Should I make a separate file for the support in Solidworks and merge it with my part in Cura? Making the support in the same STL file does not allow me to use separate materials for the part and the support.

[geert_2 556]

4 hours ago, B_Terneyre said:

Thanks for the tip, but how do I integrate the custom supports/brims in Cura? Should I make a separate file for the support in Solidworks and merge it with my part in Cura? Making the support in the same STL file does not allow me to use separate materials for the part and the support.

 

I only have single nozzle UM2 printers, so in my models everything is in the same material anyway. I need to remove these supports manually by cutting or plying. That is why I design-in features to make their removal easier (such as the ribs on top of the support). Everything, also all custom supports, are part of my CAD design, and I switch off any support in Cura.

 

For multiple nozzle printers (UM3, S5), I think in Cura you can assign different nozzles (and thus different materials) to different parts of the model. But I don't know how, so I will leave that to others here. But as soon as you start using dissolvable supports, you risk strings of that support material running through your solid parts, spoiling the watertightness.