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Shrinking PLA when using supports  

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jaychatt
(@jaychatt)
Eminent Member
Shrinking PLA when using supports

Hello. I had made an attempt at printing this cauldron.

So, I oriented it feet-down on the print bed, and chose to use supports since then the bottom would not be supported.

However, after printing and removing supports, I see that the bottom area is really, really rough. And in some areas, it has shrunk. Is this due to un-even cooling? Or some other factor?

 
This topic was modified 10 months ago 2 times by jaychatt
Posted : 12/12/2020 5:24 pm
Swiss_Cheese
(@swiss_cheese)
Noble Member
RE: Shrinking PLA when using supports

My guess would be that you should have printed the cauldron in the orientation shown on thingiverse, it probably doesn't need supports.

The Filament Whisperer...
Posted : 12/12/2020 7:12 pm
jaychatt
(@jaychatt)
Eminent Member
Topic starter answered:
RE: Shrinking PLA when using supports

@swiss_cheese

I assumed that it would need supports to make the bottom, since it would appear to be flat and just hanging out there in space, if printed like it is shown on Thingiverse.  But I'll try that next, thanks.

Just curious, though, back to mechanics of 3D printing. Is this type of thing due to uneven cooling, or other issues with PLA, that I can learn from?

Posted : 12/12/2020 7:19 pm
bobstro
(@bobstro)
Illustrious Member
RE: Shrinking PLA when using supports
Posted by: @jaychatt

[...] Just curious, though, back to mechanics of 3D printing. Is this type of thing due to uneven cooling, or other issues with PLA, that I can learn from?

It's a limitation of current consumer-grade FFF printing. You can't print large areas in mid-air, so you have to use supports. Unless you're using dissolvable supports, they need to be removable. To be removable, there has to be a gap between the supports and supported layers. This means those supported layers are literally printing in air, and gravity pulls the extrusions down. There's no layer below to squish onto, so the extrusions are round in cross-section and appear stringy. 

You can try:

  • Reorienting the part to minimize the need for supports.
  • Cutting the part into sections that can be printed without supports and assembling them after printing.
  • Doing sanding and other post-processing, usually after orienting the part to at least minimize the defect appearance.

Otherwise, it's a question of minimizing the effect but realizing you can't eliminate it. 

 

My notes and disclaimers on 3D printing and miscellaneous other tech projects
He is intelligent, but not experienced. His pattern indicates two dimensional thinking. -- Spock in Star Trek: The Wrath of Khan...
Posted : 12/12/2020 7:37 pm
jaychatt
(@jaychatt)
Eminent Member
Topic starter answered:
RE: Shrinking PLA when using supports

@bobstro

Wow that's really interesting, thanks. I had completely missed that supports weren't actually touching the layer above. I just assumed that they were. So now it makes sense, that if the support layer isn't in actual contact with the layer above, that gravity would pull the extrusion down.

Posted : 12/12/2020 8:27 pm
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