Support settings (feature request)

[Andrew1 0]

With certain materials, particularly those with strong layer adhesion and poor bridging (e.g. tpu, nylon), it is challenging to achieve dimensional accuracy and a decent finish in areas that require supports. Relatively high support density (or rather, high support interface density) is a must. I have two suggestions:

 

1) Arbitrary support z-distance/support top distance. Presently, the setting "support z distance"/"support top distance" is always rounded to a multiple of the layer height. For 0.2mm layer height, a z-gap of 0.2mm frequently results in support structures that are strongly bonded to the model. On the other hand, a 0.4mm z-gap introduces more dimensional inaccuracy and the underside contacting the support is quite rough. I tend to favor the latter option but strongly suspect a 0.3mm gap would be a good compromise. 

 

2) A setting to vertically "erode" the planar surfaces (or even just those that are horizontal) that would contact the top of support structures, by a certain distance (presumably defaulting to "support top distance"). This would make room for the extra space in the z-gap that gets taken up by the first layer built atop the support structure. To be clear, this would be a pre-processing step, with the support generated as normal afterwards, based on the adjusted model (not the original).

 

Edit: For implementing the first suggestion, the support could be built as normal up until the last few layers of the support top. Then, for example, if we have a .2mm layer height and want a .3mm gap, it could print two .15mm support layers and then skip the final support layer for a total .3mm gap , using a z-hop for moving the head to and from the support within those layers. Then the rest of the print would proceed as usual. What I mean by "arbitrary" is a reasonable range of values, say between 0x and 2x the layer height.

Edited December 18, 2022 by Andrew1

[MariMakes 206]

Hey @Andrew1,

 

Thanks for your suggestions.

I'm pretty sure that we cannot have different layerheights for parts of the model other than for adaptive layerheigths. But I'll have to check that for the team.  But I guess you can test your 0.3mm gap for sure if you change the overall layerheight to 0.15 because than you'll get 2 layers distance.

 

Regarding your second erode request. 
Would you mind sharing a picture of what you would like to see happen to the model?
Is it similar to make overhang printable where it changes to model?

Or is it similar to conical support where it changes the support?

 

[Andrew1 0]

On 12/20/2022 at 7:52 AM, MariMakes said:

Hey @Andrew1,

 

Thanks for your suggestions.

I'm pretty sure that we cannot have different layerheights for parts of the model other than for adaptive layerheigths. But I'll have to check that for the team.  But I guess you can test your 0.3mm gap for sure if you change the overall layerheight to 0.15 because than you'll get 2 layers distance.

 

The problem in this case would be that the first layer printed atop the support would have to "fall" twice its layer height. A .15mm layer taking up a .3mm gap would probably give you a similarly low-quality surface as a .2mm layer taking up a .4mm gap, albeit on a smaller scale.

 

On 12/20/2022 at 7:52 AM, MariMakes said:

Regarding your second erode request. 
Would you mind sharing a picture of what you would like to see happen to the model?
Is it similar to make overhang printable where it changes to model?

Or is it similar to conical support where it changes the support?
 

It would change the model, and the resulting support would also be different. Consider a 10x10x10mm cube floating 10mm above the built platform. If it is printed atop a support with a .4mm z-gap, then you end up with a 10x10x10.4 cube. (I tested this using cura's "standard quality" profile, the cube actually ended up 10x10x10.57, perhaps due to irregularities in the support surface.) If the model were to be adjusted so that it's a 10x10x9.6 mm cube, located at 10.4mm above the build platform the cube should be dimensionally accurate, in principle.

 

 

Incidentally, a variation on adaptive layer height could be used to achieve sub-layer-height dimensional accuracy for horizontal surfaces. (both upward and downward facing) Any time a horizontal surface is not at a multiple of the layer height, the height of the last few layers before that surface could be adjusted so that the surface is at exactly the correct height.

 

Another thought, which would really only be practical for horizontal support surfaces, might be to have the printer pause before the final layer of the support surface. Then the user could manually swap a dissolvable filament for that last layer of the support, with the printer pausing again after that part of the layer has been printed and the user swapping in the original filament. Then one could print without a z-gap (which I presume is partly the point of a dissolvable filament), at least for horizontal surfaces.

Edited January 11, 2023 by Andrew1

[Andrew1 0]

One final suggestion: When printing atop a support with a z-gap, the print lines end up being more cylindrical rather than flat. It might benefit layer adhesion if the part of the next layer that is directly above this area had an option for increased flow. Assuming a .4mm nozzle and that the lines atop a support are cylindrical, and touching but not overlapping on the sides, the additional (cross-sectional) area corresponding to one print line would be  the difference between that of a .4x.4mm square and its inscribed circle, divided by two. I've not done any experiments with this though.

 

I've been using a 3d printer for about a year now and I've found that getting smooth, dimensionally accurate supported surfaces is in general very challenging. Its sometimes difficult to work around this limitation depending on the model to be printed.

 

Edited January 12, 2023 by Andrew1

[PaulKuiper 11]

1) I do agree that a finer tuning of the airgap is useful, however this is hard to do. We will investigating strategies for this (internal reference PP-309). As you suggested, you can also print the support interface with a (soluble) support material in Cura. This saves a lot of print time because the bulk of the support structure is printed with model material and only at the interface layers a nozzle switch is required.
2) I assume that this offset is meant to improve dimensional accuracy of the (self) supported parts. In principle a good idea, we do something similar for outer and inner perimeters. Something we can look into (internal reference PP-308).
3) Printing with a higher flow on the layer above the first supported layer can be done when you are bridging. The bridging settings allow you to change the flow of the second layer. Due to a  minor bug supported regions are often marked as bridged areas so these setting might apply (check for your model, does that work as expected?).

 

 

Edited January 17, 2023 by PaulKuiper