Corners over extruded or overlapping problem

[Smithy 1,146]

Hi

 

I hope I can express my problem understandable in English (I am not a native speaker).

My problem is, that all prints have over extruded corners along the Z direction. Maybe it is not really a over extrusion, I think it has more to do with overlapping in the corners.

 

The next two pictures hopefully shows what I mean (view from the top)

 

How can I get rid of these issues? 

I am using a UM3, Cura and PLA. Haven't touched any Cura custom settings, just printed with Fast or Normal, but it is with both profiles.

 

Thanks!

BR Christian 

[owen 19]

Hi Christian

I think this occurs when the print head has to slow down for the corner and still has the plastic oozing out at the same rate which makes more plastic come out over a given distance. Maybe some plastic also gets tossed outwards when the nozzle suddenly changes direction. Either way the cure is to either print slower or if you are designing the models yourself you can make rounder corners where possible. Otherwise your prints look very good.

Owen

[Smithy 1,146]

Hi Owen

thank for your reply. So you mean, thats a more less "normal" behavior in 3D printing?

 

I am just in a deep learning about all these things and hoped there is a little custom configuration and all is good again ? I had a similar issues with the "elephant foot" and found a good hint how to avoid it. But I will try the next print with slower speed and come back if it was better.

 

For most parts it is not really an issue or only a cosmetic one, but when it comes to spare parts with fixed dimensions then it could be a problem.

 

Christian.   

[gr5 2,239]

It's not normal behavior for all printers.  It's easy to get rid of those bulging corners.

 

The UM3 default settings are designed to make the print prettier but not as accurate.  The first thing to do to help is turn off acceleration control and jerk control.  This will give you more ringing but less bulging corners because the printer won't pause so long on the corners.

 

The next thing to do is to lower your print speed closer to the corner speed.  The corner speed if it's a right angle and jerk control is off will be 14mm/sec.  If you print at 14mm/sec you will have perfect corners but even at 30mm/sec they will be much better.  20mm/sec is the slowest I ever go even when I want perfect corners.  

 

The whole reason why this works is that there is a spring effect in the bowden system and when the print head slows down (and the feeder slows down also), the pressure at the nozzle takes longer to equalize so it overextrudes when it slows down and underextrudes (briefly) when it speeds up again.

 

For this reason I also like to set ALL my printing speeds identical.  I don't want areas out of tolerance just because it slowed down after printing infill.

 

Everything is a tradeoff.  The default settings get you good results with reasonable speed but you can always tweak things to be 2X more accurate or 2X faster than default settings.

[Smithy 1,146]

Thanks gr5 for your detailed answer!

 

One more question, when you speak about lowering the speed to 20mm/sec you mean the overall "Print Speed" setting? If understood correctly, when I disable jerk and acceleration and set print speed to 20mm/sec for example, then the whole print will be printed at this speed or do I have to correct all other speed values  as well?

 

There is a lot more of learning, but it makes fun! Thanks for your help!

 

Christian

[Smithy 1,146]

I want to give an update to this topic, because it could help others (beginners) with similar issues.

 

I printed today a 20mm cube in the different Cura profiles Fine, Normal and Fast, and got some findings: In Fine - no corner issue is available (or I cannot see and feel it), in Normal you can feel it a little bit but not really noticeable and in Fast it is very present.

 

Normal thinking people would say, yes quality is lower when printing faster. And yes it is, but when the printer is quite new and you want to print a lot of things, you don't think normal (specially me) and you choose the fast option, But then you should not complain about such issues ?

 

On the other side it is exciting how to solve this effect and I will try it sometime to lower the issue in the Fast profile or better create a profile for fast prints with optimized settings.

 

Thanks to all who helped me!

Christian

[gr5 2,239]

I meant set *all* the speeds slower but most important are the shells which affect the corner bulging the most.

 

Step 1 of diagnosing is always to find a way to get it to work (e.g. in this case, turn off accel control and slow it down).  Step 2 is always find a way to make it not work (try speeding up but with accel control still off - keep speeding it up until it breaks again).  Step 3 is to try to make it work again.  Each step you learn more.  You can adjust speed and temperature *while it's printing!* to save even more time and get more experiments done in less time.  You can't change accel control while it's printing unfortunately.

 

It's not as simple as slow=good quality, fast = bad.  You can do lots of things to improve one without hurting the other.  For example print thicker layers but slow speeds and you may get the results you want (better quality *and* faster).

 

 

[Smithy 1,146]

Thanks gr5 for your explanation!

This community is great and helps a lot to understand and to learn how things play together.