I am mainly interested in the printing of thin-walled hollow models in castable resin . Preferably without , or with minimal internal supports. So I have played around with PreForm a bit and found that with fewer supports the red failure indication disappeared ! Both images of tubes without internal supports! Can I trust this outcome?
does it print that way? be interesting to see. also, are there a bunch of internal supports that are not visible in that view?
I have not yet tried to print the tube, because I am not at all certain that PreForm has generated the right number and placement of the supports. There are no internal supports.
Not sure if you oriented the piece manually or not, but I’ve noticed that each press of orient part will change the orientation. It’s not as if it makes a calculation about the optimal part orientation. You may want to cycle through multiple orient/generate supports iterations to see what it thinks is a viable way to print it.
The orientation of the tube is the same as the original stl file. So no changes. I also have tried different orientations with the same result. Less support, less failure warning. Do you mean to say that although PreForm validates this reduction of support as the way to print, it actually might not work?
I can tell you that, though it does not show any red marks on the top image (last post), it will most probably fail to print anyway, because the peel forces will be to high. As far as I know, the red indicates definite failure, but part orientation is essential to prevent failure.
Though sometimes it doesn’t make sense, like in your case; less supports = less red… Why that is I wouldn’t know…
Quick summary:
red = definite failure
no red = it’s supported enough, but if you get the orientation wrong, it will still fail.
The tube should be standing up straight like in your original post to reduce the peel forces.
PS, faint red marks don’t have to be an issue. it’s the deeper red which you should be concerned about.
Unfortunately this is not true. Red means It thinks it will fail. Sometimes it thinks it will fail but it is fine. No red means it doesn’t know of a reason for it to fail. This definitely does not mean it will not fail or that it is supported well enough it may stIll fail do to insufficient support. The red is only a helpful suggestion you can not trust it. Use you better judgement and learn how to tell if it should fail yourself.
You can’t beat experience ;). All my red marks always failed. But your response seems plausible. Would there be any deformation where the red marks are then, @RocusHalbasch?
In his first orientation he should be fine. The angle of the overhang is minimal so it should not be a problem. He might even be able to pull off printing it with only the supports that touch the end, if they anchor it adequately and the walls are thin enough so there is little adhesion during the peel process.
Very helpful suggestions, thanks. So this vertical orientation with 1.6 mm point size would probably be best? Unfortunately compared to a horizontal orientation, printing will take 7 instead of 3 hours.
Just think of it this way. Horizontally it would most probably fail. Therefore it would have taken you 10 hours in total to print it ;). Now with proper advice it’s only 7! 
And yes, that orientation should work fine!
P.S. I can’t see it properly in the picture, but the most-right support might give you a scarring on the pipe as it seems that not only the end point of the support is touching the pipe, but the side of the support is too. That leaves really bad marks and is difficult to take off without damaging the outside too much!
If the side is touching the pipe, try to adjust the angle of that support or place it a little lower.
You can probably just get rid of all of those supports that are not connected to the end, they won’t really help much at all. All of the ones at the very top will have no effect on your print till the end and if it got that far without a problem the part that remains will not be any more likely to harm your print. The on that is halfway up the side also seems unnecessary but at least will give you a little more support. However if you are concerned I would go with adding more supports at the bottom to more rigidly anchor it over having the one support half way up.
Here’s the reasoning. First you have thin walls and it is oriented so they do not run close to parallel to the platform. This means for each layer outside of the base you have very little surface area in contact with the print surface, thus you will have very little adhesion to the PDMS and that will result in very little pulling force during the peel process.This pulling force, if significant can pull you part right off the supports if you don’t have enough of them, and if they are not evenly distributed then leverage on the axis of the area your supports are localized to exacerbates this. However since you have so little surface area this pulling force will be minor so you don’t have to worry about those problems. The next problem is on tall objects if the supports are not adequate the part can have some sway resulting in the layers not lining up quite cleanly, this can in this case be improved by adding more supports at the bottom, however I would guess that in this case that the circular shape of your object and the circular positioning of you supports on the bottom should be rather stable as it is.
Rocus thanks for the detailed response . Very enlightening! I will do some test prints next week and show the results in this topic.
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