Advice needed for novice

terrypin · 2 Apr 2021 at 16:17

I'm a beginner with both 3D printing and OpenSCAD, which is so far my choice of CAD software. Hoping that this site is easier to use than both reddit and 3D printboard (with no USA/UK time zone gap as another plus).

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I started printing the top part of a box, as I'd already successfully made the larger bottom part. A few minutes later I suspected it should have been rotated 180 degs around the X-axis, or some other translation/rotation, as I doubted its stability. So I posted a query to the author:
https://www.thingiverse.com/thing:2938921/comments
and a similar query to 3Dprinboard, asking "Should I terminate this print?"
It included this screenshot:

90 mins later there were no replies, not surprisingly in view of the time zone gap, and these show the print's status:

Am I right that the model should have been inverted? If so could I have done that in Cura or any other slicing app?

Terry, East Grinstead, UK

W!ll · 2 Apr 2021 at 16:22

You would indeed have had much better success with that print if you selected the large flat surface to lay onto the bed, that is possible in most slicers and definitely possible in cura via the left hand buttons on the side of the main screen you can select the face that contacts the bed.

Another thing to consider with prints is that the orientation you print them in can greatly affect their physical properties - ie the weakest point is between the layers of the print so you try to ensure that loads are not directly applied in a way that they may pull the layers apart.

terrypin · 2 Apr 2021 at 16:43

W!ll said:
You would indeed have had much better success with that print if you selected the large flat surface to lay onto the bed, that is possible in most slicers and definitely possible in cura via the left hand buttons on the side of the main screen you can select the face that contacts the bed.

Another thing to consider with prints is that the orientation you print them in can greatly affect their physical properties - ie the weakest point is between the layers of the print so you try to ensure that loads are not directly applied in a way that they may pull the layers apart.

Thanks, appreciate the quick reply. But I'm struggling to use those 'cooling tower' icons to turn over the model!

bulb66 · 2 Apr 2021 at 16:55

terrypin said:
Thanks, appreciate the quick reply. But I'm struggling to use those 'cooling tower' icons to turn over the model!

To change it, select the model. Then click the 3rd icon down, then the 3rd icon along (Select face to align to build plate), then click the part of the model you want on the build plate.

terrypin · 2 Apr 2021 at 17:09

bulb66 said:
To change it, select the model. Then click the 3rd icon down, then the 3rd icon along (Select face to align to build plate), then click the part of the model you want on the build plate.

Got it, thanks!

Joe Jones · 3 Apr 2021 at 22:14

Pretty much all models will be supplied in the way they are designed which is often in its 'correct' visual orientation and not the way it 'should' be printed.

With the model you printed in that orientation you have pretty large bridges which for the most seasoned would be difficult to print without supports. As mentioned try to orientate the model so that the flattest part is on the bed. You could rotate the model to print it on its end but then the layer lines would be a point of weakness for that model.

terrypin · 5 Apr 2021 at 14:27

Thanks all. Reprinted after turning it over (duh!) and it was fine.

Joe: Could you expand a bit on why the layer lines would be weaker please? I've read this advice in several contexts but still don't really get it. Doing what would demonstrate this weakness?

gitbags · 5 Apr 2021 at 15:54

If the print is going to be subjected to stress you ideally want it to be along the length of the filament, this will allow for some degree of stretching before failure. Applying stress to the layers will ultimately cause the layers to separate, due to the small contact area between layers.

Think of it like wood grain.

terrypin · 5 Apr 2021 at 19:55

gitbags said:
If the print is going to be subjected to stress you ideally want it to be along the length of the filament, this will allow for some degree of stretching before failure. Applying stress to the layers will ultimately cause the layers to separate, due to the small contact area between layers.

Think of it like wood grain.

Thanks, understood.

Joe Jones · 5 Apr 2021 at 22:20

For the most part when talking about 3d printers we're actually talking about 2.5d printing. Two axes move (usually X and Y) over a stepped axis (Z) creating the layers. There is non-planar layer FDM which is pretty much true 3d printing but not used a lot and certainly not standard for printers.

The layer adhesion is a weak link because its difficult to get a good melted bond with the layer below (compared to laying down the layer where filament is fused to the parts next to it).

So if we look at the image above and think about the pictures on the right, applying forces where the arrows are shows where we that weak layer adhesion may fail. Top right would bend before a mechanical failure where bottom right would snap between the middle layers.

terrypin · 5 Apr 2021 at 22:28

Thanks Joe, that’s very helpful.