Prints "By layer" and "By object" give different results (?)

[Twitko]

I need advice from someone more experienced. I am designing a model that is quite small and has a rotating element that is printed “print in place.” Basically, it is one body with a shaft on which the second part rotates. The size of the shaft/connection is in the order of a few millimeters. The relief between the individual parts is 0.2 mm.

All of that is OK, the problem lies elsewhere. If I print the object ALONE (one piece), everything works perfectly. After printing, one slight movement is enough to release the rotating mechanism and everything works great.

However, if I print two or more of these identical objects next to each other BY LAYER (they are printed together, layer by layer), the rotating mechanism is printed incorrectly. It is basically “glued” together and almost impossible to release. About 90% of the time, it breaks when I try to release it, and even if it does come loose, the rotation basically doesn’t work, it gets stuck…

If I print the same object in multiple pieces, but set print BY OBJECT (i.e., each one is printed separately), everything is fine again. All the printed pieces are perfect… just turn it, click, and it rotates almost by itself.

To be honest, I’m at a loss - I have no idea where the problem could be. How can these two printing methods of identical object differ so much? As far as I can tell, the results from the slicer are identical - I checked it layer by layer, but haven’t found any changes or differences that would indicate that something is different here, that something will be printed differently there… afaik they are same, but final print is not.

If it were a one-time printout just for my own use, I wouldn’t worry about it… I’d just print it with BY OBJECTS and be done with it. But it’s supposed to be a public profile, so I’d like it to be foolproof… meaning that it prints properly in both modes. Plus, I’d like to understand where the hell the problem is To be honest, I don’t expect anyone to tell me exactly “the problem is exacty here”… I’d rather need at least some guidance on where to focus… what to experiment with, what to change…

It occurred to me that the filament is simply not tuned, but the same thing happens when I print from PLA Bambu, PLA from another manufacturer, PETG Devil Filament, PETG HF Bambu… I haven’t found a material that works… and I believe that otherwise I have the printer and filaments tuned quite well (well, maybe I’m wrong and something is wrong somewhere).

Just for clarity, I’m attaching a picture with the relevant detail… on the left as it is designed (and printed), on the right split into two parts for clarity… dimensions WxH 20 x 6mm, the head of the “peg” has a diameter of 4.5mm… Yes, it’s small, but as I said, it works great when printed separately, just not together…

If you know exactly what’s wrong, I’d be very grateful and thank you in advance. But even if you don’t know for sure and just have an idea, let me know… anything would help me just now thank you.

BTW, I don’t even know where to ask (in which part of the forum) … whether it’s the printer issue (I have a P1S), the filament, or whether it’s a slicer problem? So I’ll put it here … I can’t think of anything better

[blchandl2]

When printing small items like this heat/cooling can be an issue. I cannot say exactly what is causing the issue since there are multiple possibilties. Some ideas are:

1. Moisture in the filament causing stringing when moving from part to part. The moisture can cause oozing during print head travel.
2. Print head temperature. Try lowering the temp in 5 deg increments to see if that helps
3. Seam location. Seams usually have a small bulge which could be causing the problem. Combined with item #1.
4. It could also be a retraction issue.

If you can share the file I can take a look at it.

[Twitko]

Thank you for your prompt reply. Let me comment on some of your points:

1. Moisture – I don’t think this is a problem. All the filaments have been dried properly I believe) and are stored in an airtight boxes. Hygro (I know, cheap one) shows 10%. Besides, I haven’t noticed any oozing.

2. Print head temperature – good tip… I’ll try that. However, I’m confused because this concerns 4 different filaments, and I have a slightly different filament setting (temperature, shrinkage, flow …) for each of them (i.e., Devil PETG does not have the same profile as Bambu HF). But I’ll try it.

3. Seam – I’ve already thought about that and tried to manually disable the seam anywhere near the pin. It doesn’t work completely, but there are only one or two “seam dots” in the entire area… Moreover, the same seam is in the model which, printed separately, is perfect.

4. Retraction – yes, that’s a possibility. But it wouldn’t show up as some kind of stringing/oozing ?.. which I simply don’t see there…

I think it has something to do with cooling… because when the print head works on several pieces at once (layer by layer), it takes longer to return to the same spot in the next layer. Whereas when it focuses on just one (small) model, it gets back “in a moment” and there can be different conditions… but then again… 4 different filaments, 4 different temperature profiles (printing, cooling)… weird

Regarding file sharing – thank you very much for the offer, I really appreciate it, but I can’t share the file at the moment… However, I’ll try to arrange it (I’m not the only one who worked/is working on the model).

TW

[blchandl2]

One more idea. I know you said you calibrated the filament. Did you verify dimensional accuracy when you calibrated for flow ratio?

[Twitko]

yes, I did … I even printed my own test model (I use for shrinkage/dimmensional accuracy test) yesterday again, just to verify it’s still OK … not 100% perfect, but it should work here …

[Twitko]

I noticed one thing in the slicer now … if the model is alone, the Flow value is lower than when there are more models… two is enough… with a larger number of models, it doesn’t change/increase anymore. At least what I have noticed.

For Devil PETG, the Flow value is around 2.68 for one piece / and around 4.69 for multiple pieces.
For Bambu PETGHF, the value is around 3.2 for one piece / and around 4.49 for multiple pieces.

To be honest, I don’t understand why the Flow value should change depending on whether there is only one model or two/more… but this could (perhaps) be the reason for the different behavior (???)

I don’t know… this is a little beyond my knowledge and abilities… even though I’m doing my best

[blchandl2]

Interesting. One way to check would be to edit the max flow in the filament to about 3.0 and see if it helps. I will print slower but may solve the problem.

[Bullocks]

Those items are so small and so fast individually that it probably stays very hot. Temperature and plastic are interesting little monsters.

Slice the thing, go to preview, set the view to Layer Time
Do this by layer and by object to see the difference

Layer time is basically “this amount of seconds before this gets another hot pile laid onto it again” If it’s long enough to cool completely to [bed|ambient] temp, you will get a different result than if every single second, another 220degree mass is added to it.

[Twitko]

I agree… but I would expect the problem to be the opposite… that the movable joint will melt if the object is small and alone (i.e., the filament does not have time to solidify sufficiently). I already have encountered this with another project and had to solve it (despite slowing down the speed) with a “sacrificial body” where the nozzle was “busy” and was “delayed”

But in this case, it’s the opposite - where I would expect problems (short layer time), it’s fine, and where there is “enough time,” there are problems.

I’ll have to leave it for today… I’ve been struggling with it since morning, all day long, and now I’m fed up with it

BTW, thank you for your input

[Twitko]

Well, maybe I figured (a little bit) out why this is happening… it seems that the problem is the increasing FLOW RATE. If it is low (for one object in my case), it is OK. But as soon as the number of objects increases, the FLOW starts to increase and causes a problem = the rotary joint “seizes up.”

What I don’t understand here is why the Flow increases with the number of objects? (I’m not saying it’s a bug, there’s probably a reason for it… I just don’t understand it). In my case, two objects are enough for Flow to exceed the “functional value”… however, Flow increases (at least in my case/test) up to five objects, then it seems that it does not increase any further (in other models, this may of course be different).

So my questions are:

• Why does Flow increase like this?
• Can this be prevented in any way? (Apart from setting print by object)

I am attaching a few screenshots that show how Flow increases:

• from 1 to 5 objects when printing “By layers”.
• 5 objects when printing “By Object” (here the values return as if only one was printed).
• And finally, just for interest’s sake - again “By Layer” where there are “a million” objects - no difference can be seen compared to 5 objects.

BTW, test object is just a simple cube 10x10x1mm

[Bullocks]

In your filament settings, there is a setting for some time “targets” and it can slow down printing to try to hit those targets, which would look like reduced flow when not much is being printed on any given layer

its kinda hidden and poorly named, but mouseover it for the tooltip

I’m not too wild for using it for PLA at all, but it is on by default. it becomes useful when you run filament that needs zero fan.