<blockquote>
  <p>What is the reason for the external scaffolding...?</p>
</blockquote>

<p>Reading through the <a href="https://ultimaker.com/en/resources/52663-support" rel="nofollow noreferrer">Ultimaker support page</a>, I discovered that there is a <em>Support horizontal expansion</em> option in the <em>Support</em> section of the Custom Profile.</p>

<p>This appears to default to 0 mm for PLA, but defaults to 3 mm for PVA, which explains the difference in slicing behaviour.</p>

<p>If I set <em>Support horizontal expansion</em> to 0 mm, then I get the support I originally expected:</p>

<p><a href="https://i.sstatic.net/pAtNh.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/pAtNh.png" alt="Print with PVA support and Support horizontal expansion of 0"></a></p>

<p>Ultimately though, the solution proposed by <a href="https://3dprinting.stackexchange.com/users/8884/trish">Trish</a> and detailed in <a href="https://3dprinting.stackexchange.com/users/5740/0scar">Oscar</a>'s <a href="https://3dprinting.stackexchange.com/a/11004/63">answer</a> using PVA just at the interfaces would be a <em>much</em> better solution, given the cost of PVA.</p>

CC BY-SA 4.0
2019-09-13T10:05:46.993Z
This was new to me, learned something! Thanks for this answer, much appreciated!
0scar
CC BY-SA 4.0
2019-09-13T10:03:36.777Z
2019-09-13T10:03:36.777Z
Mark Booth
<p>Owning the Ultimaker 3 Extended and having printed kilometers of filament on this printer I can tell you that printing with PVA, apart from the slicing problems you mention, is not easy as it looks. PVA clogs up very fast and is very hygroscopic. Moist PVA will make popping sounds on extrusion and is prone to failing. PVA is not my preferred solution. An alternative solution is to use break-away filament, my colleagues have some reasonable good experience with that.</p>

<blockquote>
  <p>Why didn't the slicing algorithm place PVA support structures inside the overhang, in the same way as it placed the PLA support structures?</p>
</blockquote>

<p>The difference you report could be caused by the slicer settings. I get exactly the same results if you set the slicing parameter <code>Support Placement</code> to <code>Touching Buildplate</code> (first image), or <code>Everywhere</code> (second image).</p>

<p><a href="https://i.sstatic.net/AWlKOm.png" rel="nofollow noreferrer" title="`Support Placement` option `Touching Buildplate`"><img src="https://i.sstatic.net/AWlKOm.png" alt="&lt;code&gt;Support Placement&lt;/code&gt; option &lt;code&gt;Touching Buildplate&lt;/code&gt;" title="`Support Placement` option `Touching Buildplate`"></a>vs.<a href="https://i.sstatic.net/xHc76m.png" rel="nofollow noreferrer" title="`Support Placement` option `Everywhere`"><img src="https://i.sstatic.net/xHc76m.png" alt="&lt;code&gt;Support Placement&lt;/code&gt; option &lt;code&gt;Everywhere&lt;/code&gt;" title="`Support Placement` option `Everywhere`"></a></p>

<blockquote>
  <p>What is the reason for the external scaffolding, and how does it help support the internal overhang, which now has no internal support at all?</p>
</blockquote>

<p>To answer the scaffolding part of your question, that can only be explained by being the decision of the developers. There must be very good reasons for doing it like this as a similar support structure is generated in other slicers, e.g. Slic3r (actually this is caused by a slicer setting, see <a href="/a/11006/">this answer</a> explaining why the scaffolding is caused). Some slicers do have options to change the support type, e.g. Slic3r has the option <code>pillars</code>, which creates pillars without external scaffolding:</p>

<p><a href="https://i.sstatic.net/Gpzssm.png" rel="nofollow noreferrer" title="Slic3r pillars support option"><img src="https://i.sstatic.net/Gpzssm.png" alt="Slic3r pillars support option" title="Slic3r pillars support option"></a>vs.<a href="https://i.sstatic.net/pllIVm.png" rel="nofollow noreferrer" title="Slic3r rectangular support option"><img src="https://i.sstatic.net/pllIVm.png" alt="Slic3r rectangular support option" title="Slic3r rectangular support option"></a></p>

<blockquote>
  <p>Is the behaviour I expected possible, advisable or configurable in Cura? If so, what options should I be looking at, if not is there other software that does support this?</p>
</blockquote>

<p>Playing with the settings to reduce the amount of PVA as suggested in the comments by enabling the type of extruder for specific parts of the extruder I was able to create a solution without scaffolding. This solution only uses PVA for the bottom and top layer of the support structure.</p>

<p><a href="https://i.sstatic.net/edr4b.png" rel="nofollow noreferrer" title="Cura additional support extruder settings"><img src="https://i.sstatic.net/edr4b.png" alt="Cura additional support extruder settings" title="Cura additional support extruder settings"></a></p>

<p>The shown settings<sup>1)</sup> produce a support structure with PVA top and bottom layers:</p>

<p><a href="https://i.sstatic.net/1ysAhm.png" rel="nofollow noreferrer" title="Non scaffolding support structure"><img src="https://i.sstatic.net/1ysAhm.png" alt="Non scaffolding support structure" title="Non scaffolding support structure"></a>or<a href="https://i.sstatic.net/Zk35Cm.png" rel="nofollow noreferrer" title="Non scaffolding support structure in material color"><img src="https://i.sstatic.net/Zk35Cm.png" alt="Non scaffolding support structure in material color" title="Non scaffolding support structure in material color"></a></p>

<p>Where the latter image is in material color; black PLA and natural colored PVA</p>

<hr>

<p><sup>1)</sup> <em>It might be worth mentioning that by default, the Support section doesn't show the Support interface extruder options and you have to go into Preferences and check the Setting Visibility option for those to appear.</em></p>

CC BY-SA 4.0
2019-09-12T15:50:41.480Z
Ah, you're right, I was playing with the _Touching Buildplate_ earlier and must have left it enabled for the screen grab, which explains the missing fill in, but not the reason for the external scaffolding in the first place. Thanks for the PVA advice though. This is not my machine, just one I have access to, and I'm not comfortable with changing it's setup yet.
Mark Booth
CC BY-SA 4.0
2019-09-12T16:55:06.493Z
@MarkBooth I would - if I had access to a 2-head-printer with PVA, print the later from the drybox, and because of the pricetag on PVA filament, use the mode that only prints the top layers of a support structure in PVA, so that the price is reduced to a minimum.
Trish
CC BY-SA 4.0
2019-09-12T17:48:05.820Z
@Trish Guess what I bought! :) The PVA is sitting for 2 months in the drybox, will test it again soon.
0scar
CC BY-SA 4.0
2019-09-12T18:06:08.567Z
@MarkBooth Dry the filament before printing for good measure - it can't hurt. A good method can be a food dehydator.
Trish
CC BY-SA 4.0
2019-09-13T08:00:20.933Z
Thanks @Trish, It sounds like it might be worth adding an answer with this extra info. Is that mode available in Cura, or would I need to look into other software? FYI, the printer is in an air conditioned lab inside an air conditioned building. The humidity is pretty low anyway. I'll take that into consideration when I get my printer at home working though. *8')
Mark Booth
CC BY-SA 4.0
2019-09-13T08:31:26.607Z
@Trish I've updated the answer to your and Marks comments
0scar
CC BY-SA 4.0
2019-09-13T09:17:45.337Z
Very interesting, thanks for the update. I wonder if it's down to the strength of the PVA material, possibly it needs the extra structures to support itself, which is why the 'boundry only' PVA solution doesn't need that extra scaffolding.
Mark Booth
CC BY-SA 4.0
2019-09-13T10:26:00.877Z
It might be worth mentioning that by default, the _Support_ section doesn't show the _Support interface extruder_ options and you have to go into _Preferences_ and check the _Setting Visibility_ option for those to appear.
Mark Booth
CC BY-SA 4.0
2019-09-13T11:18:40.207Z
@MarkBooth Very good suggestion! This is so normal for me that I frequently forget to mention this. I have bluntly copied your comment into the answer. :)
0scar
CC BY-SA 4.0
2024-11-08T16:20:26.810Z
Looking for an answer to my problems with printing interface layers with PVA, I found this answer, confirming my decision to print dry boxes for my AMS lite.*8')
Mark Booth
CC BY-SA 4.0
2019-09-12T14:09:38.333Z
2019-09-13T14:29:38.817Z
2019-09-13T14:29:38.817Z
0scar
<p>I've just done my <a href="https://www.thingiverse.com/thing:3709044" rel="nofollow noreferrer">first print</a> on an Ultimaker 3 Extended and I'm slightly disappointed with the results, so I'm trying to understand how I can do better next time.</p>

<h2>My first print</h2>

<p>Preparing for printing I naively just dropped the two <code>stl</code> files into Cura, set the recommended layer height and infill, selected support (defaulting to Extruder 1), deselected adhesion, ran the slice, saved the g-code and started the print running. Luckily the head 1 did have the same PLA AA 0.4 filament that Cura assumed.</p>

<p>When the print finished, I stripped out the support structures, cleaning out the hollow, and cleaning off lots of stringy loose filaments between the lower support and the bottom edge of the print.</p>

<p>Even after cleaning up though, the overhanging structure above the support structure turned out to be very rough with many individual filaments visible and in irregular positions, rather than the nice concentric lines in the slice.</p>

<h2>My first attempt to optimise the print</h2>

<p>Looking at the completed print I realised that there would have been only a fraction of the support structure, and probably clean edges, if the part had been oriented as a <code>d</code> rather than as a <code>p</code> (the rough surface being the bottom of the <code>p</code> overhang).</p>

<p>I re-ran the slice in <code>d</code> orientation and that saved 10 minutes of print time, and a 100&nbsp;mm of filament, so I know I'll definitely need to look out for that in the future. I can also see how that would fix the problem with the external overhang separating out into loose threads, since that face would no longer be an overhang.</p>

<h2>Trying to add water soluble supports</h2>

<p>After the first fix, I wondered what I could do with the second extruder and realised that it was filled with water soluble PVA filament. This made me wonder if this would have helped with the internal overhang.</p>

<p>I Configured Extruder 2 as PVA BB 0.4 and selected Extruder 2 for the support structures and re-ran the slice.</p>

<p>I was surprised that the it was now taking 40 minutes longer and using almost 470&nbsp;mm more filament!</p>

<p>Looking at the slices, Cura had created a huge PVA scaffolding on the <em>outside</em> of the print, leaving the inside, where the previous PLA support had been, completely empty:</p>

<p><a href="https://i.sstatic.net/KXOTE.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/KXOTEm.png" alt="Print with PVA support"></a>vs.<a href="https://i.sstatic.net/ur5eG.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/ur5eGm.png" alt="Print with PLA support"></a></p>

<p>This was not what I was expecting.</p>

<h2>Questions</h2>

<ul>
<li><p>Why didn't the slicing algorithm place PVA support structures inside the overhang, in the same way as it placed the PLA support structures?</p></li>
<li><p>What is the reason for the external scaffolding, and how does it help support the internal overhang, which now has no internal support at all?</p></li>
<li><p>Is the behaviour I expected possible, advisable or configurable in Cura? If so, what options should I be looking at, if not is there other software that does support this?</p></li>
</ul>

<ultimaker-cura><pla><slicing><pva><ultimaker-3>
Understanding water soluble support structures
Mark Booth
# Understanding water soluble support structures

(Asked by: username_0 on 2019-09-12)

I've just done my [first print](https://www.thingiverse.com/thing:3709044) on an Ultimaker 3 Extended and I'm slightly disappointed with the results, so I'm trying to understand how I can do better next time.

## My first print

Preparing for printing I naively just dropped the two `stl` files into Cura, set the recommended layer height and infill, selected support (defaulting to Extruder 1), deselected adhesion, ran the slice, saved the g-code and started the print running. Luckily the head 1 did have the same PLA AA 0.4 filament that Cura assumed.

When the print finished, I stripped out the support structures, cleaning out the hollow, and cleaning off lots of stringy loose filaments between the lower support and the bottom edge of the print.

Even after cleaning up though, the overhanging structure above the support structure turned out to be very rough with many individual filaments visible and in irregular positions, rather than the nice concentric lines in the slice.

## My first attempt to optimise the print

Looking at the completed print I realised that there would have been only a fraction of the support structure, and probably clean edges, if the part had been oriented as a `d` rather than as a `p` (the rough surface being the bottom of the `p` overhang).

I re-ran the slice in `d` orientation and that saved 10 minutes of print time, and a 100 mm of filament, so I know I'll definitely need to look out for that in the future. I can also see how that would fix the problem with the external overhang separating out into loose threads, since that face would no longer be an overhang.

## Trying to add water soluble supports

After the first fix, I wondered what I could do with the second extruder and realised that it was filled with water soluble PVA filament. This made me wonder if this would have helped with the internal overhang.

I Configured Extruder 2 as PVA BB 0.4 and selected Extruder 2 for the support structures and re-ran the slice.

I was surprised that the it was now taking 40 minutes longer and using almost 470 mm more filament!

Looking at the slices, Cura had created a huge PVA scaffolding on the *outside* of the print, leaving the inside, where the previous PLA support had been, completely empty:

[![Print with PVA support](https://i.sstatic.net/KXOTEm.png)](https://i.sstatic.net/KXOTE.png)vs.[![Print with PLA support](https://i.sstatic.net/ur5eGm.png)](https://i.sstatic.net/ur5eG.png)

This was not what I was expecting.

## Questions

* Why didn't the slicing algorithm place PVA support structures inside the overhang, in the same way as it placed the PLA support structures?
* What is the reason for the external scaffolding, and how does it help support the internal overhang, which now has no internal support at all?
* Is the behaviour I expected possible, advisable or configurable in Cura? If so, what options should I be looking at, if not is there other software that does support this?

**Tags:** ultimaker-cura, pla, slicing, pva, ultimaker-3

---

## 2 answers

### Answer by username_1 on 2019-09-12. Score: 5 | Accepted answer

Owning the Ultimaker 3 Extended and having printed kilometers of filament on this printer I can tell you that printing with PVA, apart from the slicing problems you mention, is not easy as it looks. PVA clogs up very fast and is very hygroscopic. Moist PVA will make popping sounds on extrusion and is prone to failing. PVA is not my preferred solution. An alternative solution is to use break-away filament, my colleagues have some reasonable good experience with that.

> Why didn't the slicing algorithm place PVA support structures inside the overhang, in the same way as it placed the PLA support structures?

The difference you report could be caused by the slicer settings. I get exactly the same results if you set the slicing parameter `Support Placement` to `Touching Buildplate` (first image), or `Everywhere` (second image).

[![<code>Support Placement</code> option <code>Touching Buildplate</code>](https://i.sstatic.net/AWlKOm.png "`Support Placement` option `Touching Buildplate`")](https://i.sstatic.net/AWlKOm.png "`Support Placement` option `Touching Buildplate`")vs.[![<code>Support Placement</code> option <code>Everywhere</code>](https://i.sstatic.net/xHc76m.png "`Support Placement` option `Everywhere`")](https://i.sstatic.net/xHc76m.png "`Support Placement` option `Everywhere`")

> What is the reason for the external scaffolding, and how does it help support the internal overhang, which now has no internal support at all?

To answer the scaffolding part of your question, that can only be explained by being the decision of the developers. There must be very good reasons for doing it like this as a similar support structure is generated in other slicers, e.g. Slic3r (actually this is caused by a slicer setting, see [this answer](/a/11006/) explaining why the scaffolding is caused). Some slicers do have options to change the support type, e.g. Slic3r has the option `pillars`, which creates pillars without external scaffolding:

[![Slic3r pillars support option](https://i.sstatic.net/Gpzssm.png "Slic3r pillars support option")](https://i.sstatic.net/Gpzssm.png "Slic3r pillars support option")vs.[![Slic3r rectangular support option](https://i.sstatic.net/pllIVm.png "Slic3r rectangular support option")](https://i.sstatic.net/pllIVm.png "Slic3r rectangular support option")

> Is the behaviour I expected possible, advisable or configurable in Cura? If so, what options should I be looking at, if not is there other software that does support this?

Playing with the settings to reduce the amount of PVA as suggested in the comments by enabling the type of extruder for specific parts of the extruder I was able to create a solution without scaffolding. This solution only uses PVA for the bottom and top layer of the support structure.

[![Cura additional support extruder settings](https://i.sstatic.net/edr4b.png "Cura additional support extruder settings")](https://i.sstatic.net/edr4b.png "Cura additional support extruder settings")

The shown settings1) produce a support structure with PVA top and bottom layers:

[![Non scaffolding support structure](https://i.sstatic.net/1ysAhm.png "Non scaffolding support structure")](https://i.sstatic.net/1ysAhm.png "Non scaffolding support structure")or[![Non scaffolding support structure in material color](https://i.sstatic.net/Zk35Cm.png "Non scaffolding support structure in material color")](https://i.sstatic.net/Zk35Cm.png "Non scaffolding support structure in material color")

Where the latter image is in material color; black PLA and natural colored PVA

---

1) *It might be worth mentioning that by default, the Support section doesn't show the Support interface extruder options and you have to go into Preferences and check the Setting Visibility option for those to appear.*

> **Comments:**
> **username_0**: Ah, you're right, I was playing with the _Touching Buildplate_ earlier and must have left it enabled for the screen grab, which explains the missing fill in, but not the reason for the external scaffolding in the first place. Thanks for the PVA advice though. This is not my machine, just one I have access to, and I'm not comfortable with changing it's setup yet.  
> **username_2**: @MarkBooth I would - if I had access to a 2-head-printer with PVA, print the later from the drybox, and because of the pricetag on PVA filament, use the mode that only prints the top layers of a support structure in PVA, so that the price is reduced to a minimum.  
> **username_1**: @Trish Guess what I bought! :) The PVA is sitting for 2 months in the drybox, will test it again soon.  
> **username_2**: @MarkBooth Dry the filament before printing for good measure - it can't hurt. A good method can be a food dehydator.  
> **username_0**: Thanks @Trish, It sounds like it might be worth adding an answer with this extra info. Is that mode available in Cura, or would I need to look into other software? FYI, the printer is in an air conditioned lab inside an air conditioned building. The humidity is pretty low anyway. I'll take that into consideration when I get my printer at home working though. *8')  
> **username_1**: @Trish I've updated the answer to your and Marks comments  
> **username_0**: Very interesting, thanks for the update. I wonder if it's down to the strength of the PVA material, possibly it needs the extra structures to support itself, which is why the 'boundry only' PVA solution doesn't need that extra scaffolding.  
> **username_0**: It might be worth mentioning that by default, the _Support_ section doesn't show the _Support interface extruder_ options and you have to go into _Preferences_ and check the _Setting Visibility_ option for those to appear.  
> **username_1**: @MarkBooth Very good suggestion! This is so normal for me that I frequently forget to mention this. I have bluntly copied your comment into the answer. :)  
> **username_0**: Looking for an answer to my problems with printing interface layers with PVA, I found this answer, confirming my decision to print dry boxes for my AMS lite.*8')  

---

### Answer by username_0 on 2019-09-13. Score: 3

> What is the reason for the external scaffolding...?

Reading through the [Ultimaker support page](https://ultimaker.com/en/resources/52663-support), I discovered that there is a *Support horizontal expansion* option in the *Support* section of the Custom Profile.

This appears to default to 0 mm for PLA, but defaults to 3 mm for PVA, which explains the difference in slicing behaviour.

If I set *Support horizontal expansion* to 0 mm, then I get the support I originally expected:

[![Print with PVA support and Support horizontal expansion of 0](https://i.sstatic.net/pAtNh.png)](https://i.sstatic.net/pAtNh.png)

Ultimately though, the solution proposed by [Trish](https://3dprinting.stackexchange.com/users/8884/trish) and detailed in [Oscar](https://3dprinting.stackexchange.com/users/5740/0scar)'s [answer](https://3dprinting.stackexchange.com/a/11004/63) using PVA just at the interfaces would be a *much* better solution, given the cost of PVA.

> **Comments:**
> **username_1**: This was new to me, learned something! Thanks for this answer, much appreciated!  

---

