I did print a larger model on my P1S with PETG and tree support.
I did use the default settings except for wall loops =4 and inner fill =25%.
Everything went well until I removed the support structure just to find that the bottom layer of the bridge was a total mess.
I then tried smaller samples with similar bridge structures with different PETG and PLA materials and also with different tree support structures.
The outcome was not always as bad as on the pictures but always similarly bad.
This makes me think that there is a general problem with bridge support settings.
How can I make the bottom layer of a bridge stick together and make a solid base for the bridge?
Bridging is great to avoid supports.
Supports are great to help the bridging if it gets too long or comes with different shapes.
See it like this >
Without the supports the filament for the bridging layer prints in mid air.
So the start point is the bridge settings and getting them right so you can do longer bridges without too much sagging.
Similar story for the supports…
You want the z-distance as small as possible for a good result but not so small that things bind permanently.
The interface pattern and spacing can be a vital thing is the goal is to get clean(er) horizontal bridging results.
For example support interface in PLA and model in PETG means one can opt for a solid interface to get smoother surfaces.
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What does the support layer look like in the slicer? For a part like this, I’d use either tree hybrid or tree organic supports, as they use normal support interface nodes to rest the filament on. I’d use normal supports or the aformentioned tree options for flat supports like this to be honest, and I’d use PLA as a support interface layer as you’re using PETG
What do you mean with, how it looks like in the slicer?
I don’t see any problems there.
I used tree hybrid with a Top Z distance of 0.2mm, which is means a 1 layer gap with my 0.2mm standard printing profile.
I tried to use PLA as support in the past, but had problems with the different temperatures between PLA and PETG.
Also, with a single extruder, it would take a vast amount of time to get the support structure printed because of filament change on every single layer. Not mentioning the huge amount of wasted filament.
Or is there an option to use the support material only at the contact areas, while printing the rest of the support tree with the standard material?
Yes, you can print only the support interface layers in a dissimilar material (PETG for PLA and vice versa).
Since PETG retains heat quite well, I have found it to be rather bad at bridging/steep overhangs and does require a 0mm top distance and solid interface from PLA.
There are temp related items to take care off though. 1) The Min Max temps of the dissimilar materials must be set to temperatures in which both materials are printable. So increase the PLA Min temp to the PETG Min temp and decrease the Max temp for PETG to the Max temp of PLA in the filament settings. Min/Max is, as far as I know, only during the filament swap. So don’t worry if your print temps are out of this region. Oh, and tick the support box for your support interface material.
2) In the machine (and maybe filament) default gcode, there are unfortunately some hard numbers rather than variables. Individual entries may need to be changed if you run into problems.
Thanks for the hints, I will definitely give them a try on my next attempt.
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