Supported surface quality.

[Thunderdonkey 0]

I am new to 3D printing and still learning to use Cura.

I am printing fairly large curved panels.  I can get excellent quality on the top surface and on areas in contact with the plate, but the surface quality of the supported areas is poor.  There is no surface finishing and occasional loose lines of material.  I have the same settings for top and bottom, but bottom does not seem to mean underside.  Is there anything I can do to improve the finish on the lower surfaces?

[GregValiant 1,351]

Hello @Thunderdonkey

When you print over supports the "Support Z Distance" has two daughter commands.  The "Support Top Distance" should be 1X layer height for a single extruder printer.  I often set the "Support Bottom Distance" to 2X layer height as it makes it easier to break the support structure off when the support has to print on part of the model.

It's that top distance that is the problem with single extruder printers.  There must be a gap there or the support would be welded to the model.  Because of the gap, there just isn't much squish between the nozzle and the top of the support.

 

Another setting to consider is the "Support Interface".  You should enable it.  I like the pattern set to grid at 50% to 60% density.  That creates a better surface for that first layer of the model to extrude onto.

 

You won't get a great surface do to the lack of proper "squish" but it can be a LOT better than what you have there.  You would also want more than a single bottom skin.  It's the second skin that has a chance of squishing correctly and welding everything together.

Edited December 18, 2022 by GregValiant

[Thunderdonkey 0]

Hi Greg

Thanks for the advice, I'll try what you suggested.

Slightly baffled though.  If there is a one-layer gap between the support roof and the underside of the print, what actually happens there? Surely the underside will collapse on to the support roof.  Or am I missing something?

TD

 

[Andrew1 0]

Yes, the underside takes up the space and rests on top the support roof. The smaller the z-gap and denser the support interface, the harder it is to remove the support. I just made a feature-request thread about this topic: https://community.ultimaker.com/topic/42320-support-settings-feature-request/

 

Presumably, the real solution is to have dual extruders so that you can have a separate, dissolvable support material. I wish that more machines besides just high-end printers came with dual extruders. An extra hotend and stepper motor is no huge expense. As you've discovered it's otherwise hard to get a decent surface where supports are involved.

 

In my experience, a higher density support interface will help somewhat. Make it as dense as possible without it permanently bonding to the part. When designing a part, I will usually make an effort to minimize necessary supports.