PVA support tower breaks

[BlackCloud 1]

I'm using PLA with PVA for support on this.

 

I've been having a hella problem printing this model. The slicer creates a support tower below the protrusion shown in the pic. But it always breaks off before the tower meets the model so it just extrudes material into the air.

 

I created a test model that isolates the problem. It's five little balls hanging in mid air so that it forces support towers under them. The tiny square in the back is just to trick the slicer to keep it from moving the balls down to the build plate. I have never gotten this test to print successfully. Somewhere between one third and half way up, one of the towers breaks off and then it all goes to hell. In a few more passes all of the towers are broken. Often, but not always, they break right at the join between the brim and the wall.

 

 

I attached the test print STL if you want to play.

 

Any help would be most appreciated.
 

test4.stl

[gr5 2,167]

Well you probably need larger (wider) towers.  You can increase "horizontal expansion" for support.  It defaults I think to 3mm but you could go to 4 or 5mm.

 

Also it's important that the bottom layer squishes really well.  I'd put an EXTREMELY thin layer pva - invisibly thin - so for example use glue stick and then clean with wet tissue to spread it around (and to remove 70% of the pva).  Hopefully the PVA will stick to PVA.  Then also when it starts printing turn the 3 leveling screws a bit CCW as seen from below (try a half turn) to move the bed up and squish the PVA harder into the glass.  This will stick much better and differentiate the problem of not sticking to the glass versus not sticking to itself.  Think of this as an experiment.

 

[gr5 2,167]

Also does your PVA pop and sizzle?  If so it got too much water in it.  I've been able to "repair" nylon with water in it but have never tried PVA.  Probably put it on the heated bed at 70C for a long time - maybe a 5 days?  Under a towel or something.  I'm not sure if you can actually get the water out of PVA like you can with Nylon.

[BlackCloud 1]

The PVA is fresh. It prints out really clear, no sizzling or popping.

 

About your suggestion of smearing PVA for adhesion to the build plate, I don't think that's the problem because you can see the first few layers still intact. It actually breaks it off the brim. I'll run a few more tests and double check.

 

 

[BlackCloud 1]

You can see on this one that the break isn't at the base. 

[peggyb 169]

I would ad a cube/rectangle to the build plate and scale it so it supports all the spheres and use the 'per model settings' to give it the support settings you want. This way the support is one piece instead of multiple towers.

 

[BlackCloud 1]

I've thought about doing something like this to the model I'm trying to print. But that means every model has the potential for this problem if there are any isolated support towers generated by the slicer. It may be the only solution for now.

[kmanstudios 1,120]

It looks like what you are facing is a basic height/width ratio printing issue. Those are thin supports going up and they can be prone to getting snapped off. Try using towers in the Support areas to see if you can create a conical structure that is not just a thin column.

 

You will fijnd two sets of controls that can help get this going.

 

In support you will find "Use Towers" and can define a min and max width.

 

In experimental you will find "Enable Conical Support" which you can again define additional parameters for creating conical support structures.

 

You can also experiment with the new "Tree Structure" feature in Experimental.

 

Keep in mind, you may have to unhide these features. I have had all my settings unhidden for so long, I do not remember the basic settings available.,

[BlackCloud 1]

Did not see the conical option in the list. That may be the way to go. 

 

I tried the tree structure but it slices in odd ways. This one seems useful on a case by case basis.

[kmanstudios 1,120]

As far as I experience, everything is a case by case basis. That is why it pays to know the options and how to mix n' match. I look at it this way:

 

It is like cooking. If I tell you mix this, mix that and voila, you have a biscuit, it does not help. But If you know what the leavening does, and the baking soda does and such, you can compensate for many things that occur on a case by case basis. It ain't the recipe, it is what happens with the ingredients.

[BlackCloud 1]

Cooking? Isn't there take out? Better yet a drive through?

 

The conical option seems to do the trick.  An odd thing is that setting the angle to a positive amount creates an inverted cone. The settings for this use a -7.5 degree angle.

 

Now if I could get rid of the threads. PVA seems to be really messy. I've got retraction speed at 45mm/s and retraction distance at 9mm. Still threads like crazy. Extrusion temp is 215. Any thoughts?

 

[kmanstudios 1,120]

PVA can be messy depending on structure. I just live with it.

 

Edit: Also, depending on moisture content, it can be really much cleaner or even more dirty than you see.

Edited March 8, 2018 by kmanstudios

[jakepoz 2]

Yeah, the BB core is designed without a little "lip" on the inside of the nozzle that normally helps prevent oozing. This was a tradeoff so that you don't get carbonized material building up in there and clogging. 

[BlackCloud 1]

On 3/8/2018 at 2:47 PM, kmanstudios said:

PVA can be messy depending on structure. I just live with it.

 

Edit: Also, depending on moisture content, it can be really much cleaner or even more dirty than you see.

 I tried the experimental option "coasting" and it cleaned up some of the messiness

[kmanstudios 1,120]

58 minutes ago, BlackCloud said:

 I tried the experimental option "coasting" and it cleaned up some of the messiness

I will try that...thanks!!