Issues with bottom of supports sticking to my model  

RE:

Posted by: @amoda

• Top/Bottom Contact Z distance - 0.07

This is a very low contact distance. Try .25.

You could also try a layer height of .1 or .15. 

RE:

Can you clarify. A contact distance of 0.25 seems like a lot. Are you suggesting changing the bottom contact Z distance only? If I change the top one then I would loose the support that I have been working to gain. I can change the bottom contact, but it seems strange that I have no issue with the top releasing, yet the bottom clings so much. 

As for changing layer height, can you explain why you think that would affect the support issue? I have not had this issue before with other prints printed at 0.05. Even so, the flat part of base (up to where the supports are stuck) is already at 0.15, since there are no details there. 

RE: Issues with bottom of supports sticking to my model

My apologies, I didn't look closely enough and was assuming a nozzle size of .4 and thought the layer height was too low to get any benefit. I have no experience with the .25 nozzle, but it does seem that you could experiment with increasing the bottom contact distance to get it easier to remove. 

It kind of makes sense. Where there is a bottom of a support resting on a model area (assuming that is what you have), that first layer of support is more likely to sag and fill the contact space more. But the part of the model resting on top of the support has the advantage of bridging.  

RE: Issues with bottom of supports sticking to my model

...You could also experiment with the bottom interface layer settings. 

RE: Issues with bottom of supports sticking to my model

I'll fiddle with those settings a bit. I haven't had this issue before, but I also haven't had a lot of contact on my model. - Thanks for the feedback.

If I get it working I'll repost here for anyone else who has the same thing. If it doesn't resolve, I'll post as well. 

RE: Issues with bottom of supports sticking to my model

Well, the supports released, but they also failed to support the model as well. I'll do more tweaking. 

RE: Issues with bottom of supports sticking to my model

I'm not an expert with supports, but if you would attach your .3mf  (it has to be ZIPPED in order to be attached) perhaps someone on the forum will have more specific suggestions. 

RE: Issues with bottom of supports sticking to my model

Thanks, see attached. Though this attached version was my overnight print 'large' version for game today. (yes yes printing down to the wire) This model was printed at 0.07 with 0.1 bottom contact z distance. The supports were successful as support but also welded to the model base in some (but not all) places. In places they were not welded to the base, they certainly took some effort to remove. 

Just to summarize my testing and what I am speculating. On this model: 

• The bottom contact z distance of 0.07 was far to small as it resulted in the bottom supports being welded where they contacted the model.
• Changing the bottom contact z distance to 0.20 caused some of the supports to collapse towards the bottom which resulted in support failure on the medium sized model. (not tested on the large model)
• Changing the bottom contact z distance to 0.10 caused the supports to be welded less than 0.07, but still certainly welded in too many places. (tested on the large print overnight)
• I speculate that the contact z distance should be considered relative to the layer height rather than a static number so I have been trying to conceptualize it that way, but this gets muddied when I have variable layer height. That said, 
  • When it comes to top contact z distance:
    • Aiming for 1 to 1.5 layer height z distance at the top of the model seems to work well for gaining support when I have a few layers of interface. 
  • When it comes to bottom contact z distance:
    • Having double layer height seems to make supports a bit less resilient, though this may be able to be resolved by having wider supports (grid style) rather than snug supports. 
    • Having a single layer height or less causes the supports to weld to the model. 
    • Interface layers may play a role. I am not sure if these are helpful or hurtful at the bottom.
    • The breadth of the contact may also play a role, but this is not something I can control with how the Slicer supports work. They do not limit bottom contact to form up to layers that need support. They simply create the vertical scaffolding.  

Thank you for your help and helping me think through the logic of it. Check my thought process and let me know if you think I am brainstorming in the right direction. 

Of course, I could just blender the model into two separate parts, but I know that this may be an issue anytime I have bottom contact with the model. In short, for me it is worth figuring out the balance. 

RE: Issues with bottom of supports sticking to my model

Have you considered avoiding the bottom contact issue altogether using an angled orientation and do supports from build plate only? Also using snug supports will give you less support material to remove. 

That is some very fine sculpting there, thanks for posting the model. 

RE: Issues with bottom of supports sticking to my model

Thanks. I plan to post the model once I was satisfied with my print. 🙂

As for printing at angle, I haven't done that when I have a base just because I was worried about the base being less 'flat'. Sound advice though. Most of my prints are slotted separate from their bases so I haven't seen a base printed at angle. You may be correct that the real lesson is to avoid bottom contact supports on this one. Now that I think of it, most of my bottom contact supports have not been an issue, but typically they are very small areas. Large contact, plus heat, plus pressure, plus time may be a compounding factor.  

RE:

Also, in playing around with your suggestion (and that I did a nozzle swap this morning for a different print), I was looking back at the original Prusa settings. The defaults seem to never have interface layers on the bottom. This makes me wonder if I rabbit holed down a path with those settings incorrectly. It is possible the interface layers are playing a bigger role in the fusion than I originally suspected. 🤔 

Oh, though I should have noted in my prior post that the model is a remix of a blood elemental I found on thingverse. Which itself was a remix of a air elemental/djinn model. Anyway, makes a great dark sun pit fiend (Gustinial tar beast) in any case. 😛 

RE: Issues with bottom of supports sticking to my model

Glad you mentioned it, I had a thought that the bottom interface with spacing set to 0 could be causing it to fuse, but it slipped my mind when writing my posts. 

RE: Issues with bottom of supports sticking to my model

Update: I was going to do some more testing after printing some trees for game, but then I may have had a oozing issue which led to messing up the threads on my heat break which means my printer is out of commission for a week for parts. Booo. 

So, more to come.