PLA and PVA support interface

[AlexisHBX 0]

Hi everyone,

First time on Ultimaker forum, hope you'll be able to help !

I've been using for a couple of years a Utilmaker 3 printer with PLA in Extruder 1 and PVA in Extruder 2.
Now that Cura offers multiple parameters in support mode, I've been optimising the support interface in order to only use PVA for "Support Interface", the main support being made of PLA.

The problem I often come across is that the "Support Interface" in PVA doesn't stick to the pattern PLA support built under it.

I tried different support options but nothing really solved the issue. The only parameter helping was increasing the (PLA) support density making a more solid base for the PVA but printing time is highly impacted.
I think that maybe adding an intermediary PLA support interface full surface under the PVA support interface would help the PVA to stick to the PLA support.
But I'm unsure this configuration exists.
Has anyone find a way of composing support this way ?

Thanks for your help !

 

[tinkergnome 926]

10 hours ago, AlexisHBX said:

The only parameter helping was increasing the (PLA) support density making a more solid base for the PVA but printing time is highly impacted.

 

There's a setting called "Gradual Support Infill Steps" (and a corresponding step height). This may work for your purpose.

[AlexisHBX 0]

I've looked into this setting and it could well help.
I'll start a print tomorrow to check the result.
Thanks for the tip !

[NBull 14]

I would advise you to keep a close look on your printer when using "Gradual Infill" settings. this setting has caused my printer to fail badly more then ones. And one of the times it was close to do damage to the print head.

 

I have had a good experience using Pla for all support settings (15% density) and only Pva on Support roof and floor setting. to give the Pva some more structure i set up the "support roof/floor thickness" to both 0.6mm. 

 

If you have problems whit the Pva sticking to the Pla try and increase the Pva tempter a few degrease.

[ultiarjan 1,222]

39 minutes ago, NBull said:

I would advise you to keep a close look on your printer when using "Gradual Infill" settings. this setting has caused my printer to fail badly more then ones. And one of the times it was close to do damage to the print head.

 

Now I'm curious... what happened? and how is it related to gradual infill?

[NBull 14]

This was caused by the Gradual Infill setting. and i have same problem on other models that else print perfect whit out this setting. 
I'm not 100% sure why it fails, but it tend to be in ariers where there are a certain amount of details on a small space. At theis areas the printer keep putting on to much material until the extruder had to dige a grove in the plastic. 

 

At this example there was so much excess material that it could reach the bottom of the extruder head. and tore apart the silicone cover.

 

(Sorry I don't remember the Cura version, maybe it have been fixed.)

 

[kmanstudios 1,120]

Try upping the support interface thickness.

 

On a more 'hands on' approach, I have taken to  making certain support structures to do exactly what you are doing. I do it to not waste so much expensive PVA materials. Here is an example:

 

 

I used material colour in the right view so you could see it properly. This involves making the left side prism as a separate object to give it different properties. Single walled to cut down on material usage. Surprisingly, it printed quite well.

 

On the left side

Red is the PLA and blue is the PVA.

 

On the right side, the grey is the PLA and the cream colour is the PVA. I have done this for many models to cut down on PVA usage. The support model only needs to be able to hold the PVA ok.

 

Keep in mind that some PLA brands and/or colours do not always adhere to the PVA at times.

[geert_2 556]

If you design custom support structures, maybe you could add sort of dovetail things in it? (I hope this is the correct English word.)  Like they used to do in old woodworking.

 

See this: the bottom red symbolises the custom support, the middle white is the PVA, and the top red is the real model.