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I am at the moment designing some in place mechanical parts. Something like two cylinders that rotate with respect to each other. I need in my design some overhangs that cannot be printed and I was thinking of using soluble supports to be able to print these overhangs. I am afraid that by using something like PVA the PVA will end up between the two parts and glue the together.

Does anyone have any experience with this? Can something be done about this apart from 'not using PVA'?

Edit:

Here is an (minimal) example of an object I would be worried about. The blue and red cylinders are supposed to turn around each other and there is a cutout in the blue cylinder that will need support (the bridge is to long to print without support).

enter image description here

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  • $\begingroup$ Maybe you can add an image of the print design or printed object? $\endgroup$
    – 0scar
    Dec 17 '18 at 13:42
  • $\begingroup$ Are you planning to have support in between your cylinders, or does the support need to be elsewhere and you're afraid it'll go between your cylinders unintentionally? $\endgroup$
    – Dan Hulme
    Dec 17 '18 at 13:59
  • $\begingroup$ @DanHulme support should be somewhere else and I am afraid that it will go in between the cylinderspenscad $\endgroup$
    – E Doe
    Dec 17 '18 at 15:17
  • $\begingroup$ You know the PVA support comes out solid, right? It doesn't just ooze into places like squirting PVA glue out of a tube. $\endgroup$
    – Dan Hulme
    Dec 17 '18 at 15:21
  • $\begingroup$ Yes I do know, but I am afraid that once you start to dissolve it in water the PVA will start to ooze into the crevices. $\endgroup$
    – E Doe
    Dec 17 '18 at 15:31
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You've not stated this, but one must presume that you have a dual or multi-material extruder equipped printer.

Because PVA dissolves in water, the supports will be eroded on contact when the part is immersed. As the PVA dissolves, it increases the concentration of PVA in the water, but only slightly. You would have to agitate the water, change it if you feel it is becoming too concentrated. At some point, you should be able to rotate the cylinders, creating more turbulence, causing more PVA to dissolve into the water.

If you are determined enough, you can cause all of the PVA to dissolve, followed by a rinse with clean water. This would remove any residual PVA.

The water containing the dissolved PVA is somewhat sticky, but would not glue parts together if the parts were thoroughly rinsed. It's not out of the question to use an ultrasonic cleaner with plain water to provide sufficient turbulence, again changing the water periodically to keep the concentration low.

If you use an ultrasonic cleaner, test a sample of your print filament to determine if the heat generated will soften the plastic. I've had success with PVA to the extent that I have not had to use an ultrasonic cleaner to remove it.

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  • $\begingroup$ Out of curiosity, did you try to print something similar with PVA supports? I do have the feeling that this procedure would work, essentially trying to keep the concentration of PVA in the water low so it won't stick the parts together. At the moment I do not have a multi material printer, so I cannot try it out. But in the past I tried to have these kinds of models printed (through a printing service), which failed miserably, therefore I want to know if anyone has any (real world) experience with this. I am happy to provide a model if that helps. $\endgroup$
    – E Doe
    Dec 18 '18 at 14:26
  • $\begingroup$ The smallest PVA print I've done is one that required a 2mm gap. $\endgroup$
    – fred_dot_u
    Dec 18 '18 at 15:41
  • $\begingroup$ With moving parts? and 2mm is way to big for 'smooth' motion in the system I want to print. $\endgroup$
    – E Doe
    Dec 20 '18 at 10:00

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