Why would multiple objects not print the same?

Bambu Lab H2 Series
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I printed one of these neat little bag clips, in PETG if it matters, and it came out really well. Moves perfectly, no binding at all, no force needed to get it to initilly open.

I then printed a set of 6. Cloned them in the slicer, didn’t make any other change at all.

Every single one of the next set won’t open. It’s hard to tell, but I think it’s that the lever (the bottom section) is fused to the bottom of the jaw. I’ve even tried using a bit of force to get them to initially open but no luck, the lever will break before it opens.

So, I printed another single one. It worked perfectly again.

Can anyone tell me why a single one would print perfectly,but multiples of the same object fail this way? It has me stumped.

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There are many factors, the most likely would be this, at least to me.

Tolerances in the model are likely very tight, when you clone the model, they now span more of the build plate, with 6 chosen, none will be in the exact centre, heat distribution isn’t as perfect as you might imagine and thus could change how the molten filament cools.

Essentially, portions of the bottom layers have fused together as they were not perfectly cooled instantly.

The increased print time per layer also plays a factor in the cooling. You could try print by object if you initiate use Bambu Studio.

Changes in temperature can affect prints in this way as well. You indicate you have a H2 series printer which by design has venting, so it is likely you had the door closed, so this is less likely a factor.

Build plate maintenance could play a roll, far too few know they need cleaning, far fewer do it correctly. Given 6 failed, it is unlikely to be a factor as that likelihood is very limited to have come on all over those places at the same time.

As an experiment, you may wish to try a test print with five, one in each corner and one dead centre. Remove them one at a time to see which if any work. You need to use Bambu Studio for this.

Make sure the door is closed.

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Thanks Marc :slight_smile:

That makes sense and I think you’re spot on.

After I posted I started another print with just 2 copies. These did both work but weren’t quite as easy to initially open as when I printed just the one. Hence, I think exactly what you said came into play, but with only 2 and not 6 it didn’t quite cause enough of a problem to stop them functioning.

Thanks!

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I would have gone with “layer time”.

The print shrinks as it cools. If you’re only printing one, the shrinkage from one layer to the next is minimal. When you print many, layer time goes way up, shrinkage increases.

The same effect causes a bulge on an outer wall, that’s aligned with the top surface inside the wall. “Benchy Hull Line” issue.

If the model has very tight tolerances, and the layer-to-layer misalignment increases, things will get stuck together.

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Yup, agreed Rocket. It’s probably a combination of everything suggested.

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They seem like a small item. You could try printing by object rather then by layer if you want multiples on one plate.

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My guess:
I would also say it is due to layer time, but not because of cooling but because of speed: a single item will be printed really slow to maintain minimum layer time and therefore very precise. multiple copies will print faster and if flow dynamics is not perfect, the seam might be bulging and fuse to the next part.

To test this: slice a single part and in preview, select speed view. find out, which speed is used for the outer walls.
In preparation, set the same speed for outer walls and see if multiple copies work now.

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I have the same issue. Why does it increase speed with multiple objects whilst reducing the quality?

In my case I print an object made with OpenScad and put a text layer on it in Bambu Slicer. I print the object with the main nozzle of my X2D and, to spare fillament, the text layer with the side nozzle. If I print this only once, it has very good quality and it takes 30minutes. If I copy the exact same model 4times onto the plate, it only takes 68 minutes (so only around double the time while 4 times the objects) but the quality especially of the text layer is garbage. It has bubbles, you can see through the layer and the see the dark object below. You can see the single lines the nozzle prints and not a closed surface.

I didn’t change any speeds or quality preferences in the process settings (globally or per object) whilst copying, so the settings from the one item is the same as the copied objects, but nevertheless it doesnt’t print them the same way. It even prints the first object of the 4 in the exact same place as the one object, when I only print a single piece. So it’s not about the heating differences on the plate.

As I print by object, it is also not about layer time or something. Actually it prints the same object, only not once but 4 times. But it prints them not in the same quality. The only further difference, besides the quality, is the fillament tower, that the slicer adds automatically, if you only print one piece (even with dual nozzle on my X2D it adds the tower), but deletes it automatically, if you put in multiple pieces.

And it gets even stranger: If I combine my four objects into one object in Bambu Lab before slicing, it will only take like 70 minutes, but the quality will be as good as if I only print one piece. It uses the fillament tower then as well, because it only sees my 4 objects as one.

Obviously, the slicer is “optimizing” something in the backend when you change from one object to multiple objects. It deletes the fillament tower but increases speeds somehow, too. I don’t know if the increased speed (less likely because of the good result with the workaround with combining the 4 objects into one) or the deletion of the fillament tower reduce the quality of the model (more likely, but strange on the other hand because of the fual nozzle in X2D).

How can I change that and forbid all optimizations but tell the slicer to print the exact same object with the exact same settings 4 times instead of once? Or can I force him to use a fillament tower with multiple objects as well?