Ugly surface using support structure

[payghamwa 0]

Hi guys,

I have an issue with the UM3 Ext, as the surface of the overhangs with support structure is really bad. Cura and the printer should have latest firmwares. Can you tell me how I can solve this problem? I attached a picture of a test part.

Many thanks in advance.

[geert_2 557]

I don't have an UM3, so this is only a guess: from the photo there appears to be a way too big gap between support structure and bottom of the model. So the first layers of the model do sag. Also it looks like the support structure is not dense enough: not enough contact points between support and model for good support. I can't comment on the cause: a problem in the design? Or a problem with underextrusion of the support material? Or wrong settings?

[payghamwa 0]

Thanks for your comments. Unfortunately I have this issue with every part I print. Also put the settings into default but this didn't help. Support material comes from the same extruder like the actual part, so I don't think underextrusion is a problem :(

[yyh1002 60]

First turn on the hidden setting of support Z distance.

THE SOLUTION:

The minimum support Z gap is 1 time layer height if you don't want them totally fused together. What you can do is to change the support Z distance to 0.1 for 0.1mm layer height, 0.15 for 0.15 layer, etc. And also turn on the complete support interface. That's going to give you better bottom.

THE RANT:

The default should be 0.4 for 0.2 layer, and 0.2 for 0.1 layer, which I totally disagree.

The double layer height Z gap is guaranteed to produce horrible bottom like what you have. I don't know why Cura has default like these.

Imagine there is a 0.4mm gap, plus the 0.2 for the print layer itself, the nozzle would be 0.6mm away from the support surface, even larger than the 0.4mm nozzle diameter itself. How is that ever gonna work? Cura probably don't do over-extrusion to compensate for the gap either.

Same thing for the default gap for raft settings. 0.3 gap for 0.1mm layer. I honestly don't know how that could work.

Edited September 25, 2017 by Guest

[mastory 44]

I have had good results using the optional support roof, the particulars I can't remember, but it basically makes much more dense (by user definition) top on the support. It's perfect for horizontal overhangs.

I can't see the other side of your part, or know its desigb intent, but it looks like it may be better suited to printing inverted.

[kmanstudios 1,120]

You say that the support comes out of the same extruder as the part. So i am assuming you are not using PVA? That can help a lot and you can let the model sit on the support roof.

[ryandavidson 1]

Try turning on "Enable support interface" and reducing "Support Z distance". I had the same issue as you and this seems to help a lot

[kmanstudios 1,120]

Try turning on "Enable support interface" and reducing "Support Z distance". I had the same issue as you and this seems to help a lot

Not a good idea if using the same material for support as the model. If using PVA it works wonders, but if using same material as the model, it will bond to it like a wall.

[mastory 44]

With a single nozzle machine like my UMO, the options are more limited. I sometimes split my model in 2 horizontally, and place the 2 halves split side down on the glass. The resulted glued part has a very consistent flat glue joint, and 2 printed top surfaces, and no supported surface on the finished part. Otherwise, have used the support roof option both with and w/o the support interface. I think the support interface can be set to undrrextrude which allows for better separation. I would like to explore a using very dense support roof (think top surface) with a dense, but thin and underextruded interface and zero distance to the supported surface.

[gr5 2,172]

Well you have a UM3 so the obvious answer is to use PVA support.

There are other great answers above but... can't you rotate the model such that the edge that is pointing downwards in the photo is the bottom? Cura has the ability to rotate your part in any axes. Click on the part and on the left side choose the icon for rotating then click on a circle and drag.

[arthurmsarthur 0]

I am going to try to bring this topic back in discussion since I am struggling with similar issues. 

I have an Ultimaker S5 printing out of one nozzle with PLA, using the 0.8mm nozzle. 

One picture shows a CURA screenshot with the support settings: I followed the suggestions of this thread and changed the default Z-distance to the same as the layer height, 0.4mm. I enabled the support roof to see if it would help, even knowing it would be harder to remove. 

You guys will see pictures of the final piece once I removed the support. 

 

I am still getting a rough finish, both on curved and on flat surfaces over supports. I understand that some of the issues comes from using a 0.8mm nozzle that doesnt come out as nice as the other ones, but I still believe I should be able to print this piece coming out better. I just wanted to hear opinions from the experts here. 

 

And I could print the piece with the flanged surface facing down, but I am trying to keep the internal surface of the print looks good, the outside is not as important. But this is what I will try next, change the orientation and see how the printer will handle the support over the curved external surface. 

 

Thank you in advance for the feedback!!!

 

 

[gr5 2,172]

If you are going to print it upside down like this then:

1) The curved surface - right where it leaves the print bed - is much steeper (more horizontal) than 45 degrees.  You can't get good quality on surfaces that steep without PVA support.  So: would it be so horrible to make it 45 degrees initially as it leaves the flat part?  And then blend into a curve?

 

2) The brim of your "hat" is simply underextruded because it was over support and gently fell down onto the support.  Not squishing out as normal.  So again, PVA support is a good option here.

 

It's okay (even recommended) to do 0.8 nozzle with PLA on the left extruder and 0.4 nozzle PVA on the right extruder (BB 0.4 seems to waste less PVA).

[Framar 38]

Reducing the Z distance to 0,3 or even 0,2mm might help improving the surface finish.

[arthurmsarthur 0]

1 hour ago, gr5 said:

If you are going to print it upside down like this then:

1) The curved surface - right where it leaves the print bed - is much steeper (more horizontal) than 45 degrees.  You can't get good quality on surfaces that steep without PVA support.  So: would it be so horrible to make it 45 degrees initially as it leaves the flat part?  And then blend into a curve?

 

2) The brim of your "hat" is simply underextruded because it was over support and gently fell down onto the support.  Not squishing out as normal.  So again, PVA support is a good option here.

 

It's okay (even recommended) to do 0.8 nozzle with PLA on the left extruder and 0.4 nozzle PVA on the right extruder (BB 0.4 seems to waste less PVA).

 

You are right on point 1. Will try to change the design taking this into consideration. 

I was trying to avoid using PVA and keep everything with PLA, I understand that most of the issues I am having will probably be solved with the use of PVA. It just adds time and cost to the prints. 

 

[arthurmsarthur 0]

44 minutes ago, Framar said:

Reducing the Z distance to 0,3 or even 0,2mm might help improving the surface finish.

 

I will try that next time. Thank you for the advice guys!

[geert_2 557]

3 hours ago, Framar said:

Reducing the Z distance to 0,3 or even 0,2mm might help improving the surface finish.

 

Yes, that could work. But it could also fuse the support into the model, making it very hard to remove the support without extensive cutting and damaging the model. You have to test this first on a small test-model with variations.

 

If I would have dual nozzle machines, I would use PVA-support in this case. However, to minimise PVA consumption and to maximise stability, I might custom design most of the supports to be printed in PLA, and only do a small PVA interface in-between. And I would use a sort of dovetail to make the PVA- and PLA-supports grip well onto each other. I can't try this of course, no dual-nozzle printers, but I believe it should work. The support would of course be a tree-like structure for good stability but economic material use. See this pic for the basic idea. See further down for simple tree-like structures.

 

On my single nozzle UM2 printers, I use various techniques to make support removal easier, also in hard to reach areas, but still keep the bottom of the real model acceptable. However, this bottom inevitably has visible lines and gaps, as you have noticed. Otherwise it would fuse totally with the supports. Ribs do make tighter gaps possible (usually the ribs are 0.5mm wide, separated 1mm from each other). Idem for printing cooler. Also, printing small separate chunks with provisions for inserting hooks, knifes, and tools for pulling hard, makes tighter tolerances possible.

 

This will take trial and error on small test pieces, to see what works for your materials, temperatures, models and speeds.

 

 

 

 

 

 

 

 

[arthurmsarthur 0]

1 hour ago, geert_2 said:

 

Yes, that could work. But it could also fuse the support into the model, making it very hard to remove the support without extensive cutting and damaging the model. You have to test this first on a small test-model with variations.

 

If I would have dual nozzle machines, I would use PVA-support in this case. However, to minimise PVA consumption and to maximise stability, I might custom design most of the supports to be printed in PLA, and only do a small PVA interface in-between. And I would use a sort of dovetail to make the PVA- and PLA-supports grip well onto each other. I can't try this of course, no dual-nozzle printers, but I believe it should work. The support would of course be a tree-like structure for good stability but economic material use. See this pic for the basic idea. See further down for simple tree-like structures.

 

On my single nozzle UM2 printers, I use various techniques to make support removal easier, also in hard to reach areas, but still keep the bottom of the real model acceptable. However, this bottom inevitably has visible lines and gaps, as you have noticed. Otherwise it would fuse totally with the supports. Ribs do make tighter gaps possible (usually the ribs are 0.5mm wide, separated 1mm from each other). Idem for printing cooler. Also, printing small separate chunks with provisions for inserting hooks, knifes, and tools for pulling hard, makes tighter tolerances possible.

 

This will take trial and error on small test pieces, to see what works for your materials, temperatures, models and speeds.

 

 

 

 

 

 

 

 

 

That is actually a really good idea. I am tried to reduce the Z-distance a little more now and will see how that goes but that for sure is something worth trying. We will have quite a lot of pieces to produce coming up and if I can come up with a bullet-proof way to print them it would make life easier a little bit. I will explore this idea more. 

 

[gr5 2,172]

Well if you don't want to wast tons and tons of filament with these tests, please do small test cases.